Microstructural, Mechanical and Corrosion

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metals Article

Microstructural, Mechanical and Corrosion Investigations of Ship Steel-Aluminum Bimetal Composites Produced by Explosive Welding Yakup Kaya

ID

Technology Faculty, Karabük University, Karabük 78050, Turkey; [email protected]; Tel.: +90-370-418-7100  

Received: 19 June 2018; Accepted: 12 July 2018; Published: 15 July 2018

Abstract: In this study, explosive welding was used in the cladding of aluminum plates to ship steel plates at different explosive ratios. Ship steel-aluminum bimetal composite plates were manufactured and the influence of the explosive ratio on the cladded bonding interface was examined. Optical microscopy (OM), scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) studies were employed for the characterization of the bonding interface of the manufactured ship steel-aluminum bimetal composites. Tensile-shear, notch impact toughness, bending and twisting tests, and microhardness studies were implemented to determine the mechanical features of the bimetal composite materials. In addition, neutral salt spray (NSS) tests were performed in order to examine the corrosion behavior of the bimetal composites. Keywords: bimetal composite; features; corrosion

explosive welding;

ship steel;

aluminum;

mechanical

1. Introduction Today’s ship and offshore construction designers face complex problems in selecting materials that provide minimization of topside weight and protection against marine corrosion-all within a reasonable budget [1]. With the development of modern industry, applications of single metallic constituents are unable to meet these requirements. Instead, with the respective merits of two metallic components, the bimetal clad plate is capable of achieving the performance that single metal constituents fail to provide [2]. The usual solution to this problem is to employ a variety of metals throughout the structure, each being selected for features appropriate for the specific component [3]. Cladded plates are used today in power plants, for applications in the chemical and petrochemical industry, for desalination plants, in ship construction, etc. In particular, the formation of a metallic continuity of metal combinations that are difficult or impossible to bond by other means is desirable for other applications, such as the automotive and the aerospace industries. Light-weight metals, like titanium, aluminum, and even magnesium can be bonded to other metallic partners like steel or to each other [4]. Aluminum alloy displays the ideal features of low density, high thermal conductivity, and good corrosion resistance [2,5]. Steel/aluminum structural transition joints (STJ) are widely used in the ship-building industry due to the important weight-saving advantages of joining these two materials, while exploiting their best features [6–8]. In this arrangement, the total weight of the ship is reduced due to the lighter aluminum superstructure [7,8]. Bars and plates that are made of steel/aluminum alloys with thicknesses greater than 20 mm are of relevant interest. At present, explosive welding is predominantly used to join this material combination. No alternative commercial technology is available that is capable of directly bonding these dissimilar materials with thick proportions [9].

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Pure aluminum is used to achieve a satisfactory bond in the steel-aluminum explosive welding. Pure aluminum, thanks to its high melting point, zero freezing range, and high thermal conductivity, reduces the amount and duration of the liquid phase, thereby preventing the formation of fragile intermetallic compounds at the bonding interface. In previous works [10–12], steel-(pure) aluminum Metals 2018, 8, x FOR PEER REVIEW 2 of 15 joints have been successfully achieved using the explosive welding method. However, previous studies havePure used only the traditional techniques of optical microscopy (OM)explosive and scanning aluminum is used to achieve a satisfactory bond in the steel-aluminum welding.electron microscopy (SEM) forthanks microstructure examinations with some tests (tensile-shear, Pure aluminum, to its high melting point, zeroalong freezing range, andmechanical high thermal conductivity, reduces theevaluations, amount and duration of the liquid phase, thereby formation of fragilewas not bending) in their while the corrosion resistance ofpreventing these andthe similar composites intermetallic compounds at the bonding interface. In previous works [10–12], steel-(pure) aluminum investigated by exposure under service conditions. joints have been successfully achieved using the explosive welding method. However, previous The purpose of this study was to produce a bimetal composite for ship-building applications studies have used only the traditional techniques of optical microscopy (OM) and scanning electron by cladding plates(SEM) of ship steel to aluminum platesalong and to examine the ability of(tensile-shear, explosive welding microscopy for microstructure examinations with some mechanical tests to join ship steel and aluminum. In addition to conventional microstructural methods (OM and bending) in their evaluations, while the corrosion resistance of these and similar composites was not SEM), the composites were examined area and linear energy dispersive spectrometry (EDS) investigated by exposure under servicevia conditions. Themechanical purpose of this study was to produce a bimetalas composite for ship-building applications by were analyses, and tests (tensile-shear, bending) well as notch impact and torsion tests cladding plates of ship steel to aluminum plates and to examine the ability of explosive welding to applied. Finally, corrosion resistance was determined by neutral salt spray (NSS) tests (in seawater) in join ship steel and aluminum. In addition to conventional microstructural methods (OM and SEM), accordance with the proposed use of the composites. the composites were examined via area and linear energy dispersive spectrometry (EDS) analyses, and mechanical tests (tensile-shear, bending) as well as notch impact and torsion tests were applied. 2. Experimental Procedure Finally, corrosion resistance was determined by neutral salt spray (NSS) tests (in seawater) in thesteel proposed useplate) of the composites. In accordance this study,with ship (base and aluminum plates (flyer plate) were bonded via the

explosive welding method. The chemical compositions of the ship steel and aluminum plates are 2. Experimental Procedure given in Table 1. The dimensions of the ship steel and aluminum plates were 250 × 150 × 5 mm In this study, ship steel (base plate) and aluminum plates (flyer plate) were bonded via the and 250 × 150 × 2 mm, respectively. The explosive material, supplied by MKE Barutsan Company explosive welding method. The chemical compositions of the ship steel and aluminum plates are (Ankara, Turkey), was Elbar-5 (92% ammonium nitrate, 5.0% fuel-oil, and 3.0% TNT). Preliminary given in Table 1. The dimensions of the ship steel and aluminum plates were 250 × 150 × 5 mm and experiments were carried out to determine thematerial, explosive ratiosbytoMKE be used in the experimental 250 × 150 × 2 mm, respectively. The explosive supplied Barutsan Company (Ankara, studies and four different werenitrate, determined (R = and 2, R3.0% = 2.5, R =Preliminary 3, and R experiments = 3.5, R being the Turkey), was explosive Elbar-5 (92%ratios ammonium 5.0% fuel-oil, TNT). were out to determine explosive ratios toCladding be used inoperations the experimental and four weight of thecarried explosive/the weightthe of the flyer plate). were studies performed three times different explosive ratios were determined (R = 2, R = 2.5, R = 3, and R = 3.5, R being the weight of the for each explosive ratio using the welding parameters in Table 2. A parallel arrangement (Figure 1) explosive/the weight of the flyer plate). Cladding operations were performed three times for each was used for the welding setup. explosive ratio using the welding parameters in Table 2. A parallel arrangement (Figure 1) was used for the welding setup.

Table 1. The chemical composition (wt.%) of ship steel and aluminum. Table 1. The chemical composition (wt.%) of ship steel and aluminum.

Elements % Weight

Elements % Weight

Ship Steel Ship Steel Aluminum Aluminum

C

C

Mn

Mn

Si

Si

Al

Al

Cu

Cu

0.149 0.1490.7 0.7 0.1660.166 0.028 0.028 0.049 0.049 Balance 0.07 0.61 0.07 0.61 Balance 0.25 0.25

Cr

Cr

0.022 0.022 0.097 0.097

Mg

Fe

Mg Fe Balance - - Balance 0.92 0.92 0.20 0.20

Table2.2.Welding Welding parameters. Table parameters. Explosive Explosive ExplosiveExplosive Explosive Explosive Density Speed−1 Type Type Density (g/cm3 ) 3 Speed (ms ) (g/cm ) (ms−1) Elbar-5 Elbar-5

0.8

0.8

3000–3200 3000–3200

Stand-off Flyer Plate Explosive Explosive Stand-off Flyer Plate Explosive Explosive Distance, s WeightWeight (g) Ratio (R) (g) Distance, s (mm) (g) Ratio Amount (R) Amount (g) (mm) 2 400 2 400 2.5 500 2.5 500 200 ± 5 2 2 200 ± 5 3 600 3 600 3.5 700 3.5 700

Figure 1. Parallel arrangement of experimental setup for explosive welding process (reproduced from

Figure 1. Parallel arrangement of experimental setup for explosive welding process (reproduced [13], with permission from Springer, 2018). from [13], with permission from Springer, 2018).

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For microstructural, mechanical, and corrosion characterization samples were taken from the For characterization samples sampleswere weretaken takenfrom fromthe the Formicrostructural, microstructural, mechanical, mechanical, and and corrosion corrosion characterization bimetal composites. The samples for metallographic observations were cut from the bimetal bimetal composites. The samples for metallographic observations were cut from the bimetal composites bimetal composites. The samples for metallographic observations were cut from the bimetal composites parallel to the explosion direction. The samples were ground and polished to a 3 μm parallel to theparallel explosion direction. Thedirection. samples were ground and a 3polished µm finish composites to the explosion The samples werepolished ground to and to and a 3 then μm finish and then etched using solutions of 2.5 percent nital for the ship steel and Keller’s reagent for etched using solutions 2.5 percent forpercent the ship steel reagent for thereagent aluminum. finish and then etched of using solutionsnital of 2.5 nital forand the Keller’s ship steel and Keller’s for the aluminum. The metallographic examinations of the samples were implemented using a Nikon The metallographic examinations of the samples were implemented using a Nikon Epiphot 200 optical the aluminum. The metallographic examinations of the samples were implemented using a Nikon Epiphot 200 optical microscope (Nikon, Melville, NY, USA). A ZEISS EVO LS 10 (Carl Zeiss SMT microscope NY,(Nikon, USA). A ZEISS EVO LS 10 A (Carl Zeiss SMT Epiphot 200(Nikon, optical Melville, microscope Melville, NY, USA). ZEISS EVO LSGmbH, 10 (CarlOberkochen, Zeiss SMT GmbH, Oberkochen, Germany) scanning electron microscope equipped with energy dispersive Germany) scanning electron microscope equipped energy dispersive (EDS) was GmbH, Oberkochen, Germany) scanning electronwith microscope equipped spectrometry with energy dispersive spectrometry (EDS) was used to characterize the microstructure and composition of the bimetal used to characterize microstructure and composition of the bimetal bonding spectrometry (EDS)the was used to characterize the microstructure and composite composition of theinterface. bimetal composite bonding interface. composite bonding changes interface.in the bimetal composite plates were determined using a Shimadzu HV Microhardness Microhardness changes in the bimetal composite plates were determined using a Shimadzu HV Microhardness the bimetalTokyo, composite plates wereload determined usingduring a Shimadzu HV microhardness tester changes (MCT-W,inShimadzu, Japan). A 500-g was applied tests. Each microhardness tester (MCT-W, Shimadzu, Tokyo, Japan). A 500-g load was applied during tests. Each microhardness value tester (MCT-W, Shimadzu, Tokyo, Japan). A 500-g load was applied during tests. Each microhardness was the average of three indentations. In order to determine the mechanical microhardness value was the average of three indentations. In order to determine the mechanical microhardness value was the average of three indentations. In order features of the bimetal composite samples, three samples were usedto fordetermine each test the andmechanical the results features of the bimetal composite samples, three samples were used for each test and the results were features of the bimetal composite samples, three samples were used for eachD3165-07 test and the results were were averaged. Tensile-shear tests were implemented according to ASTM (Figure 2)using while averaged. Tensile-shear tests were implemented according to ASTM D3165-07 (Figure 2) while averaged. Tensile-shear tests were implemented according to ASTM D3165-07 (Figure 2) while using using a Shimadzu testing machine unit (Shimadzu, Tokyo, Japan). 3 shows the dimensions a Shimadzu testing machine unit (Shimadzu, Tokyo, Japan). FigureFigure 3 shows the dimensions of a testing machine unit (Shimadzu, Tokyo, Japan). Figure 3 shows the dimensions of a ofaCharpy aShimadzu Charpy (V-notch) impact test specimen. Charpy (V-notch) impact tests were doneatat room room (V-notch) impact test specimen. Charpy (V-notch) impact tests were done Charpy (V-notch) impact test specimen. Charpy (V-notch) impact testsout were done at room temperature Bending tests were were carried in accordance accordance with temperatureon onaaCharpy Charpy impact impact test test machine. machine. Bending tests carried out in with temperature on a Charpy impact test machine. Bending tests were carried out in accordance with ASTM A 263-12. The bending tests were applied to the bimetal composites to check the strength ASTM A 263-12. The bending tests were applied to the bimetal composites to check the strength of A 263-12. The bending tests were applied to the bimetal to checkout the strength of ofASTM thecladding cladding samples under different conditions. The composites tests carried two ways: the of of thethe samples under different conditions. The tests were were carried out in twoinways: with the cladding of the samples under different conditions. The tests were carried out in two ways: with with the aluminum cladding material retained inside and the aluminum material the aluminum cladding material retained inside and with thewith aluminum cladding cladding material retained the aluminum cladding materialtests retained inside and composite with the aluminum cladding material retained retained outside. The twisting of the bimetal plates were applied manually with outside. The twisting tests of the bimetal composite plates were applied manually with a torque outside. The twisting tests of the bimetal composite plates were applied manually with a torque awrench. torque wrench. In to order to examine the corrosion behavior of the composite materials seawater water In order examine the corrosion behavior of the composite materials in in a asea wrench. In order to examine the corrosion of unit the composite intests/salt a sea water environment, were performed using abehavior SAL 600 600 TL according tomaterials corrosion spray environment,NSS NSStests tests were performed using a SAL TL unit according to corrosion tests/salt environment, NSS tests were performed using a SAL 600 TL unit according to corrosion tests/salt test standard EN ISO 9227 (for evaluation of resistance to corrosion of metal materials temporarily spray test standard EN ISO 9227 (for evaluation of resistance to corrosion of metal materials spray testpermanently standard ENprotected, ISO 9227or(for evaluation of resistance to corrosion of metal materialsto protected, unprotected against corrosion). The NSS tests applied temporarily protected, permanently protected, or unprotected against corrosion). Thewere NSS tests were temporarily protected, permanently protected, or unprotected against corrosion). The NSS tests were the bonding of theinterface composite (covering both materials) forboth the determination the applied to interface the bonding of samples the composite samples (covering materials) forofthe applied to the bonding interface ofNaCl) the composite samples (covering both materials) for the corrosion resistance in sea water (5% of the base material (ship steel) and cladding material determination of the corrosion resistance in sea water (5% NaCl) of the base material (ship steel) and determination of the corrosion resistance in sea water (5% NaCl) of the base material (ship steel) and (aluminum) used in(aluminum) the production composite materials. cladding material usedof inthe thebimetallic production of the bimetallic composite materials. cladding material (aluminum) used in the production of the bimetallic composite materials.

Figure 2. Schematic representation of tensile-shear test samples. Figure of tensile-shear tensile-shear test test samples. samples. Figure 2. 2. Schematic Schematic representation representation of

Figure 3. Schematic representation of Charpy impact test samples. Figure 3. 3. Schematic Schematic representation representation of Figure of Charpy Charpy impact impact test test samples. samples.

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3. Results and Discussions

3. Results and Discussions

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Figures 4–6 show microstructure images at different magnifications of the bonding interfaces of 3. Results and Discussions Figures 4–6 show microstructure images at different magnifications of the bonding interfaces of the ship steel-aluminum bimetal composite materials produced via the explosive welding method. the ship steel-aluminum bimetal composite materials produced via the explosive welding method. Metallographic Examination All of3.1. the images show the ship steel asasthe and the thealuminum aluminum flyer plate. All of the images show the ship steel thebase baseplate plate and asas thethe flyer plate. Figures 4–6 show microstructure images at different magnifications of the bonding interfaces of the ship steel-aluminum bimetal composite materials produced via the explosive welding method. All of the images show the ship steel as the base plate and the aluminum as the flyer plate.

Figure 4. Images of bimetal composites bonding interfaces according to explosive ratios.

Figure 4. Images of bimetal composites bonding interfaces according to explosive ratios. Figure 4 shows that a flat interface was obtained in the bonding interface at the lowest explosive

Figure that a flat interface was obtained in the bonding at the lowest explosive ratio (R4= shows 2). Waving can be to start in the bonding interface as theinterface explosive ratio was increased Figure 4. Images of seen bimetal composites bonding interfaces according to explosive ratios. (R = 2.5). As the explosive ratio was further increased (R = 3), significant increases in wavelength ratio (R = 2). Waving can be seen to start in the bonding interface as the explosive ratio was increased (400–500 µ m) and amplitude m)was were seen ininthe interface. The interface Figure 4 shows that aratio flat (~120 interface obtained the bonding interface at thebonding lowestinexplosive (R = 2.5). As the explosive was µfurther increased (Rbonding = 3), significant increases wavelength with the highest wavelength (500–600 µ m) and amplitude (~160 µ m) was the bimetal composite ratioµm) (R = and 2). Waving can be seen µm) to start in the bonding the explosive was increased (400–500 amplitude (~120 were seen in the interface bondingasinterface. The ratio bonding interface with sample that at thewas explosive ratio(R(R= =3), As the explosive ratio increased, (R = 2.5). Aswas the produced explosive ratio further increased significant increases in wavelength the highest wavelength (500–600 µm)highest and amplitude (~160 µm)3.5). was the bimetal composite sample that the collision velocity of the flyer plateµ(aluminum) increased, and thus, the impact (400–500 µ m) and amplitude (~120 m) were seen in the bonding interface. Thepressure bondingincreased. interface was produced at the highest explosive ratio (R = 3.5). As the explosive ratio increased, the collision With the thishighest pressure increase, the deformation rate increased(~160 and µthe in thecomposite interface with wavelength (500–600 µ m) and amplitude m) fluctuation was the bimetal velocity of thedue flyer plate (aluminum) increased, and thus, theasimpact pressure increased. With this increased to produced the rise inatthe rate. As a result, the ratioratio increased, the sample that was thedeformation highest explosive ratio (R = 3.5). As explosive the explosive increased, pressure increase, the deformation rate(aluminum) increased and the the interface increased waving at the bonding interface increased and parallel to fluctuation this, the wavelength and the amplitude the collision velocity of the flyer plate increased, and thus, theinimpact pressure increased. due to theWith rise in the deformation rate. As a result, as the explosive ratio increased, the waving increased. the literature [14],the it was reported that generated during this In pressure increase, deformation ratea pressure increasedwave and isthe fluctuation in the explosive interfaceat the bonding interface and parallel to this, the wavelength the amplitude increased. welding process, the base plate and flyer plate specific andexplosive usually very velocities. increased due increased to which the risegives in the deformation rate. As a result, as and the ratiohigh increased, theIn the 5 Pa. This The collision ofbonding plates with suchaincreased high velocities triggers pressure of up 1-2and atmthe ×welding 10amplitude literature [14], was reported that pressure wave is generated during thetoexplosive process, waving at itthe interface and parallel toa this, the wavelength pressure makes itliterature possible to obtain states under static loads. In addition, increased. In the [14], it wasphysical reported that aunattainable pressure wave is generated during the explosive which gives the base plate and flyer plate specific and usually very high velocities. Thesome collision previous studies havethe reported that and increasing amount increased collision welding process, which gives base plate flyer plate specific usually very of plates with such [15–19] high velocities triggers aanpressure ofexplosive up to and 1-2 atm × 105 high Pa.thevelocities. This pressure rate collision and impact pressure, and these, invelocities turn, caused the joining interface to change from a5 Pa. straight The of plates with such high triggers a pressure of up to 1-2 atm × 10 makes it possible to obtain physical states unattainable under static loads. In addition, some This previous form to amakes wavy itone. It wastoalso reported that an increase in theunder amount of loads. explosive increased the pressure possible obtain physical states unattainable static In addition, some studies [15–19] have reported that an increasing explosive amount increased the collision rate and wavelength and amplitude. previous studies [15–19] have reported that an increasing explosive amount increased the collision impact pressure, and these, in turn, caused the joining interface to change from a straight form to rate and impact pressure, and these, in turn, caused the joining interface to change from a straight a wavy one. was also that an increase the amount explosive increased the wavelength form to aIt wavy one.reported It was also reported that aninincrease in theofamount of explosive increased the and amplitude. wavelength and amplitude.

Figure 5. Image of morphologies formed at bonding interface in bimetal composites.

Additionally, ship steel wave folding (mechanical locking) occurred in the bonding interface and folded partsFigure were locked aluminumformed flyer plate due tointerface the impact pressure that is generated in 5. Imageinofthe morphologies at bonding in bimetal composites. 5. increase Image ofinmorphologies at bonding interface bimetal composites. parallel Figure with the the explosiveformed ratio (Figure 5). These wavein folds and the locking increase the interface surface area. The increase in the bonding surface field results in the development of Additionally, ship steel wave folding (mechanical locking) occurred in the bonding interface and bonding interface strength. It has been noted in the literature [20–22] that a wavy bonding interface Additionally, ship steel in wave folding (mechanical locking) occurred in thethat bonding interface folded parts were locked the aluminum flyer plate due to the impact pressure is generated in and is parts usually desirable in in explosive welding, ratio since(Figure it ensures atolarger bonding interface fieldisasgenerated well as parallel with the increase in the explosive 5). These folds and the locking increase folded were locked the aluminum flyer plate due thewave impact pressure that in greater bonding strength. Moreover, small peninsular island-shaped ship steel sections canincrease be the interface surface area. Theexplosive increase in the bondingand surface field results inand the the development of parallel with the increase in the ratio (Figure 5). These wave folds locking observedinterface on the aluminum side ofbeen the bonding interface. These[20–22] small islands are thought to interface have left bonding strength. It increase has noted the literature that a wavy the interface surface area. The in theinbonding surface field results inbonding the development of theusually ship steel and formed at the bonding as an effect of the pressure generated is desirable in explosive welding, interface since it ensures a larger bonding interface fieldduring as wellthe as bonding interface strength. It has been noted in the literature [20–22] that a wavy bonding interface greater bonding strength. Moreover, small peninsular and island-shaped ship steel sections can be is usually desirable in explosive welding, since it ensures a larger bonding interface field as well as observed on the aluminum side of the bonding interface. These small islands are thought to have left greater Moreover, smallinterface peninsular island-shaped steel sections can be thebonding ship steelstrength. and formed at the bonding as anand effect of the pressureship generated during the

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observed on the aluminum side of the bonding interface. These small islands are thought to have Metals 2018, 8, x FOR PEER REVIEW 5 of 15 left the ship steel and formed at the bonding interface as an effect of the pressure generated during the explosive In previous previousstudies studies[13,23], [13,23], was reported peninsular island-like explosive welding. welding. In it it was reported thatthat peninsular and and island-like morphologies could be formed at the interface as an effect of the detonation force and metal vortex morphologies could be formed at the interface as an effect of the detonation force and metal vortex flow flow during high explosive welding. during high explosive welding. Metals 2018, 8, x FOR PEER REVIEW

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explosive welding. In previous studies [13,23], it was reported that peninsular and island-like morphologies could be formed at the interface as an effect of the detonation force and metal vortex flow during high explosive welding.

Figure 6. Image of grains near the bonding interface extending in the explosion direction in bimetal Figure 6. Image of grains near the bonding interface extending in the explosion direction in composites. bimetal composites.

Furthermore, grains that were close to the bonding interface extended parallel to the explosion

Figure 6. Image of grains near the bonding interface extending in the explosion direction in bimetal Furthermore, grains that welding. were close the bonding extended parallel to the explosion direction during explosive Thistoeffect graduallyinterface disappeared at distances moving further composites. direction explosive effect gradually disappeared at distances further awayduring from the interface welding. (Figure 6). This Mastanaiah et al. [24] reported that grains close to moving the welded were generally elongated parallel to the explosion direction and were caused by the highly awayinterface from the interface (Figure 6). Mastanaiah et al. [24] reported that grains close to the welded Furthermore, grains that were close to the bonding interface extended parallel to the explosion localized plastic deformation occurring during theexplosion collision between theand plates. Additionally, direction during explosive welding. This effect disappeared at distances moving further interface were generally elongated parallel togradually the direction were caused by Athar the highly and Tolaminejad [25] reported that an increase in the explosive ratio might affect not only theAthar away from the interface (Figure 6). Mastanaiah et al. [24] reported that grains close to the welded localized plastic deformation occurring during the collision between the plates. Additionally, bonding interface morphology, of the field that affected by the deformation. were generally elongated parallel tothe thedepth explosion direction andiswere caused by the highly andinterface Tolaminejad [25] reported thatbut analso increase in the explosive ratio might affect not only the bonding localized plastic deformation occurring during the collision between the plates. Additionally, Athar interface morphology, but also the depth of the field that is affected by the deformation. 3.2.Tolaminejad SEM and EDS and [25]Analysis reported that an increase in the explosive ratio might affect not only the

bonding interface morphology, but also the depth of the field that is affected by the deformation.

show SEM images and EDS analyses of the bonding interfaces for the different 3.2. SEM Figures and EDS7–10 Analysis explosive All of the images show the upper field as the ship steel base plate and the lower field 3.2. SEM andratios. EDS Analysis

Figures 7–10 show as the aluminum flyerSEM plate.images and EDS analyses of the bonding interfaces for the different Figures 7–10 SEM images and EDS analyses of the bonding the different explosive ratios. Allshow of the images show the upper field as the ship interfaces steel baseforplate and the lower field explosive ratios. flyer All of plate. the images show the upper field as the ship steel base plate and the lower field as the aluminum as the aluminum flyer plate.

Figure 7. (a) Scanning electron microscopy (SEM) image of bimetal composite bonding interface for R = 2 and (b–d) energy dispersive spectrometry (EDS) analysis results of the indicated areas.

Figure Scanning electron (SEM) imageimage of bimetal composite bonding interface forinterface for Figure 7. 7.(a)(a)Scanning electronmicroscopy microscopy (SEM) of bimetal composite bonding R = 2 and (b–d) energy dispersive spectrometry (EDS) analysis results of the indicated areas. R = 2 and (b–d) energy dispersive spectrometry (EDS) analysis results of the indicated areas.

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The SEM image of the composite bonding interface that is produced at the lowest explosive ratio (Figure 7) shows a flat interface was obtained. As aisresult of the analysis performed The SEM imagethat of the composite bonding interface that produced at EDS the lowest explosive ratio on the fields7) indicated on athe image, theobtained. chemicalAsfeatures asperformed Fe (98.42%)onfor (Figure shows that flatSEM interface was a resultwere of thedetermined EDS analysis thethe base fields indicated SEM image, wereplate determined as Fe (98.42%) for the base of Fe plate materialoninthe Field-1 and asthe Al chemical (91.90%) features for the flyer material in Field 3. The presence plate material in determined Field-1 and as (91.90%) forthough the flyer plate material 3. The presence Fe on the (96.18%) was in Al Field-2 even this region closeintoField the joining interfaceofwas (96.18%) was determined in Field-2 even though this region close to the joining interface was on the Al (the flyer plate material). In addition, Al (1.81%) and oxide (2.01%) residues were detected in very Alsmall (the flyer plate material). In addition, Al (1.81%) and residues were detectedininthis very quantities in Field-2. In conclusion, it can beoxide said (2.01%) that there was no diffusion welding small quantities in Field-2. In conclusion, it can be said that there was no diffusion in this welding operation where the lowest explosive ratio (R = 2) was used. operation where the lowest explosive ratio (R = 2) was used.

Figure 8. (a) SEM image of bimetal composite bonding interface for R =for 2.5Rand (b–d) analysis Figure 8. (a) SEM image of bimetal composite bonding interface = 2.5 andEDS (b–d) EDS analysis results of the indicated areas. results of the indicated areas.

The SEM image of the composite bonding interface produced at the R = 2.5 explosive ratio The SEM image of the composite bonding interface produced at the R = 2.5 explosive ratio (Figure 8) shows the waving that started in the bonding interface. As a result of the EDS analysis that (Figure 8) shows the waving that started in the bonding interface. As a result of the EDS analysis was performed on the fields indicated on the SEM image, the chemical features of the base plate that was performed on the fields indicated on the SEM image, the chemical features of the base material of Fe (97.71%) in Field-1 and of the flyer plate material of Al (96.66%) in Field-3 were plate material of Fe (97.71%) in Field-1 and of the flyer plate material of Al (96.66%) in Field-3 were determined. On the other hand, Field-2 on the bonding interface was found to consist of determined. On the hand, on the interface was found toliterature consist of[26] approximately approximately 78% Al,other 18% Fe, andField-2 4% oxide. Thebonding Fe-Al balance diagram in the was 78% Al,and 18% Fe, and 4% balance from diagram in the literature [26] was examined examined showed that theoxide. FeAl3 +The αAl Fe-Al layer occurred the sub-eutectic temperature of 652 and showed that the FeAl + αAl layer occurred from the sub-eutectic temperature of 652 ◦ C to 3 °C to room temperature. room Thetemperature. SEM image of the composite bonding interface produced at the R = 3 explosive ratio (Figure The SEM of occurred the composite interface produced in at the the bonding R = 3 explosive ratio 9) 9) shows that an image increase in thebonding wavelength and amplitude interface. As(Figure a shows that an increase occurred in the wavelength and amplitude in the bonding interface. As a result result of the EDS analysis that was performed on the fields indicated on the SEM image, the chemical of the EDS analysis that was performed on the fields indicated the chemical features of the base plate material of Fe (98.55%) in Field-1 andon of the theSEM flyerimage, plate material of Alfeatures (87.48%) in Field-3 determined. However, theofbase of Fe close the of the base platewere material of Fe (98.55%) in Field-2 Field-1 on and the plate flyer material plate material of Alto(87.48%) in bonding was found toHowever, consist of approximately Al,plate 48% Fe, and 1%of oxide. By examining Field-3interface were determined. Field-2 on the51% base material Fe close to the bonding theinterface Fe-Al balance diagram the of α2 layer was determined, in which 35–50% of the Fe and atoms was found to [26], consist approximately 51% Al, 48% Fe, and 1% oxide. ByAl examining the had dissolved into each other room temperature. Moreover,inthe linear35–50% EDS analysis on Fe-Al balance diagram [26],atthe α2 layer was determined, which of the performed Fe and Al atoms had this field confirmed theother results. dissolved into each at room temperature. Moreover, the linear EDS analysis performed on this

field confirmed the results.

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Figure 9. 9. (a)(a) SEM interfacefor forRR==3;3;(b) (b)EDS EDSanalysis analysis results Figure SEMimage imageofofbimetal bimetalcomposite composite bonding interface results of of Figure 9. (a) SEM image of bimetal composite bonding interface for R = 3; (b) EDS analysis results of the indicated line; and,(c–e) (c–e)EDS EDSanalysis analysisresults results of of the indicated areas. the indicated line; and, indicated areas. the indicated line; and, (c–e) EDS analysis results of the indicated areas.

Figure 10. (a) SEM imageofofbimetal bimetalcomposite composite bonding bonding interface for RR==3.5 and EDS analysis Figure SEM image interface and(b–d) (b–d) EDS analysis Figure 10.10. (a) (a) SEM image of bimetal composite bonding interface for R =for 3.5 and3.5 (b–d) EDS analysis results of the indicated areas. results of the indicated areas. results of the indicated areas.

The SEM image of the composite bonding interface produced the highest explosive ratio = The SEM image of the bonding interface produced at theathighest explosive ratio (R = (Rratio The SEM image ofcomposite the the composite bonding interface produced at the highestwere explosive 3.5) was the image where wavelength and amplitude in the bonding interface the most 3.5) was the image where the wavelength and amplitude in the bonding interface were the most (R evident = 3.5) was the image where the wavelength and amplitude in the bonding interface were the most (Figure 10).a As a result the EDS analysis that performed was performed onfields the fields indicated on the evident (Figure 10). As result of theofEDS analysis that was on the indicated on the evident (Figure 10). As a result of the EDS analysis that was performed on the fields indicated on image, the chemical features ofbase the base material Fe (96.81%) in Field-1 andflyer the flyerthe SEMSEM image, the chemical features of the plateplate material of Feof(96.81%) in Field-1 and the SEM image, the chemical features of the base plate material of Fe (96.81%) in Field-1 and the flyer plate material Al (90.18%) in Field-3 determined. The Field-2 region onflyer the flyer material plateplate material of Alof (90.18%) in Field-3 werewere determined. The Field-2 region on the plateplate material material of Althe (90.18%) in Field-3was were determined. 96% The Field-2 regionand on the flyer plate material of Al Al near joining interface approximately Al,oxide, 4% oxide, of Alofnear the joining interface was approximately 96% Al, 4% and 0.4%0.4% Fe. Fe.

near the joining interface was approximately 96% Al, 4% oxide, and 0.4% Fe.

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As a result, it was found that a flat interface was obtained with a low explosive ratio and no intermetallic formation was observed. In addition, as the explosive ratio increased, the wavy structure formed by mechanical interlocking occurred at the interface and some intermetallic compounds were formed. It is thought that the low explosive ratio at the interface did not generate a high enough temperature to 8, create intermetallic forms, while at high explosive ratios, the temperature was reached Metals 2018, x FOR PEER REVIEW 8 of 15 at which intermetallic forms could be seen as part of the interface. As a result, it was found that a flat interface was obtained with a low explosive ratio and no intermetallic formation 3.3. Tensile-Shear Test Results was observed. In addition, as the explosive ratio increased, the wavy structure formed by mechanical interlocking occurred at the interface and some intermetallic Table 3 shows theformed. tensile-shear test that results of the bonding for the explosive compounds were It is thought the low explosive ratiointerfaces at the interface did different not generate a ratios. high It is seen thattemperature the tensile-shear strength increased by approximately at increasing explosive enough to create intermetallic forms, while at high10% explosive ratios, the temperature could be composite seen as part interface of the interface. ratios (from R = 2 was to Rreached = 3.5). atAswhich seenintermetallic in Figure 4,forms the bimetal transits from a flat

form to a wavy one at increasing explosive ratios, and the bonding interface field increases as a result 3.3. Tensile-Shear Test Results of increasing wavelength/amplitude. Moreover, wave folding (mechanical locking) was formed in 3 showsbonding the tensile-shear testdue results bonding for the different explosive from the bimetalTable composite interface to of thethe impact of interfaces the pressure that was generated ratios. It is seen that the tensile-shear strength increased by approximately 10% at increasing the increase in the explosive ratio (Figure 5). As a result, the tensile-shear strength increased with the explosive ratios (from R = 2 to R = 3.5). As seen in Figure 4, the bimetal composite interface transits expanded bonding interface field and the wave folding. from a flat form to a wavy one at increasing explosive ratios, and the bonding interface field increases as a result of increasing wavelength/amplitude. Moreover, wave folding (mechanical locking) was Table 3. Tensile-shear test results of bimetal composite samples. formed in the bimetal composite bonding interface due to the impact of the pressure that was generated from the increase in the explosive ratio (Figure 5). As a result, the tensile-shear strength Tensile-Shear Strength (MPa) increased with the expanded bonding interface field and the wave folding. R=2 R = 2.5 R=3 R = 3.5 Ruptured Material Table 3. Tensile-shear test results of bimetal composite samples.

28.5 ± 1

29.4 ± 1

31.5 ± 1

32.1 ± 1

Aluminium

Tensile-Shear Strength (MPa) R=2 R = 2.5 R=3 R = 3.5 Ruptured Material Tolaminejad [25] that that were 28.5 ± 1 reported 29.4 ± 1 31.5 ± 1wavy 32.1 ±interfaces 1 Aluminium

Athar and generated from increases in explosive ratio and impact pressure expanded the bonding interface field, which subsequently Athar and Tolaminejad reported wavy interfaces thatthat werethe generated increases increased tensile-shear strength [25] slightly. Thethat authors also added impactfrom pressure andinsudden explosive ratio and impact pressure expanded the bonding interface field, which subsequently shock hardening, due to the increasing explosive ratio, and the grain refinement, due to the cold increased slightly. The authorsstrength. also addedIn that the impact pressure deformation in tensile-shear the bondingstrength field, resulted in greater another study, Xie etand al. sudden [27] reported shock hardening, due to the increasing explosive ratio, and the grain refinement, due to the cold that waving in the bonding interface ensured better mechanical locking between the flyer plate and deformation in the bonding field, resulted in greater strength. In another study, Xie et al. [27] reported the base plate andinhigher bonding interface strength. that waving the bonding interface ensured better mechanical locking between the flyer plate and The fracture images after the tensile-shear test (Figure 11) show that there was no separation in the base plate and higher bonding interface strength. the bonding in anyafter of the composite samples; occurred Theinterface fracture images the bimetal tensile-shear test (Figure 11) showhowever, that there cracking was no separation in in the bonding interface of the bimetal composite samples; however, cracking in the upper the aluminum plate in in allany composites produced at different explosive ratios.occurred According to these aluminum plate in all composites produced at different explosive According to these results,upper the aluminum cladding material was successfully bonded ontoratios. the ship steel base material aluminum cladding material was successfully bonded onto the ship steel base material surfaceresults, whilethe using the explosive welding method. Bimetal composite plates were produced by surface while using the explosive welding method. Bimetal composite plates were produced by Li et Li et al. [2] (Al/Fe), Asemabadi et al. [28] (Al/Cu) and Loureiro et al. [29] (Cu/Al) and using the al. [2] (Al/Fe), Asemabadi et al. [28] (Al/Cu) and Loureiro et al. [29] (Cu/Al) and using the explosive explosive welding method, andreported they reported thattensile-shear after tensile-shear no separation was welding method, and they that after tests, no tests, separation was seen in theseen in the bonding interface. bonding interface.

Figure 11. Macro images of bimetal composite samples after the tensile-shear test.

Figure 11. Macro images of bimetal composite samples after the tensile-shear test. 3.4. Charpy Impact Toughness Results

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Table 4 shows the Charpy impact toughness test results of the samples at room temperature. Samples of 55 × 10 × ~7 mm in dimension were used. The impact toughness of the bimetal composite Table 4 shows the Charpy impact toughness test results of the samples at room temperature. samples decreased as the explosive ratio increased. The amount of deformation in the materials had Samples of 55 × 10 × ~7 mm in dimension were used. The impact toughness of the bimetal composite increased due to the increased pressure in parallel with the increasing explosive ratio. The decrease in samples decreased as the explosive ratio increased. The amount of deformation in the materials had impact toughness dependent on the explosive ratio was a result of high plastic deformation. In a similar increased due to the increased pressure in parallel with the increasing explosive ratio. The decrease study, Kaya and Kahraman [1] produced Grade A/AISI 316L bimetal composite plates while using the in impact toughness dependent on the explosive ratio was a result of high plastic deformation. In a explosive welding method at different explosive ratios, and the results of the Charpy notch impact similar study, Kaya and Kahraman [1] produced Grade A/AISI 316L bimetal composite plates while toughness test showed that deformation hardening increased as a result of an increasing explosive using the explosive welding method at different explosive ratios, and the results of the Charpy notch ratio, and thus, the impact toughness of the bimetal composites decreased. impact toughness test showed that deformation hardening increased as a result of an increasing explosive ratio, and thus, the impact toughness of the bimetal composites decreased. Table 4. Charpy impact test results of ship steel/aluminum bimetal composite.

Table 4. Charpy impact test results of ship steel/aluminum bimetal composite. Charpy Impact Test (Joule) Charpy Test (Joule) R = 2 Impact R = 2.5 R=3 R = 3.5 Ship steel/aluminum R = 2 R = 2.5 R = 3 R = 3.5 36.5 ± 1 35 ± 1 33.5 ± 1 33 ± 1 Ship steel/aluminum 36.5 ± 1 35 ± 1 33.5 ± 1 33 ± 1

Figure of samples subjected to to the the notch notch impact impact toughness toughness test test at at room room Figure 12 12 shows shows macro macro images images of samples subjected temperature. When the macro images of samples after the notch impact toughness test were examined, temperature. When the macro images of samples after the notch impact toughness test were no separation was seen in anyseen of the bimetal composite samples that were that produced at different examined, no separation was in any of the bimetal composite samples were produced at explosive ratios. Cracking occurred in the ship steel (base plate) side of the ship steel-aluminum bimetal different explosive ratios. Cracking occurred in the ship steel (base plate) side of the ship steelcomposites and although bending seen in the aluminum plate) side, no separation was aluminum bimetal composites andwas although bending was seen(cladding in the aluminum (cladding plate) side, present. Kaçarwas andpresent. Acarer [30] cladded P355GH AISI 316L and and reported that after notch impact no separation Kaçar and Acarer [30]and cladded P355GH AISI 316L and reported that toughness at different temperatures, crackingtemperatures, was present on the basewas material only after notchtests impact toughness tests at different cracking present on(P355GH), the base while no only cracking was seen on the claddingwas material material (P355GH), while no cracking seen (AISI on the316L). cladding material (AISI 316L).

Figure the notch notch impact impact toughness. toughness. Figure 12. 12. Macro Macro images images of of bimetal bimetal composite composite samples samples after after the

3.5. Bending Test Results 3.5. Bending Test Results Figure 13 shows macro images that were obtained as a result of the (two-way) bending tests Figure 13 shows macro images that were obtained as a result of the (two-way) bending tests applied to the ship steel-aluminum bimetal composite samples that were produced via explosive applied to the ship steel-aluminum bimetal composite samples that were produced via explosive welding with the cladding plate (aluminum) extending both inwards and outwards. No visible welding with the cladding plate (aluminum) extending both inwards and outwards. No visible cracks, fractures, or separations were seen in the bonding interface of the bimetal composite samples cracks, fractures, or separations were seen in the bonding interface of the bimetal composite samples produced at different explosive ratios as a result of the two-way bending tests performed by bending produced at different explosive ratios as a result of the two-way bending tests performed by bending the samples 180°. the samples 180◦ .

Figure 13. Macro images of bimetal composite samples after the bending test.

Figure 13 shows macro images that were obtained as a result of the (two-way) bending tests applied to the ship steel-aluminum bimetal composite samples that were produced via explosive welding with the cladding plate (aluminum) extending both inwards and outwards. No visible cracks, fractures, or separations were seen in the bonding interface of the bimetal composite samples produced at544 different explosive ratios as a result of the two-way bending tests performed by bending Metals 2018, 8, 10 of 15 the samples 180°.

Figure Figure 13. 13. Macro Macro images images of of bimetal bimetal composite composite samples samples after after the the bending bending test. test.

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The fact that no faults were found in the bonding interfaces of the bimetal composite samples as a result of the bending tests indicates that a safe safe welding welding was was achieved, achieved, and and these these bimetal bimetal composites composites also reported reported in in literature literature [12,31–33] [12,31–33] that that explosively explosively could safely be used under service conditions. It also materials could could be bended bended up to 180°. 180◦ . As As there there was was no no defect (cracks (cracks or seperation) seperation) in the cladded materials interfaces of the bended specimens, they can can be be readily readily used used in in the thebended bendedform formin inservice serviceconditions. conditions.

3.6. Twisting Twisting Test 3.6. Test Results Results ◦ twisting test applied Figure 14 14 shows shows macro macroimages imagesthat thatwere wereobtained obtainedasasa aresult resultofofthe the 360twisting Figure 360° test applied to ◦ twisting test was applied to to the ship steel-aluminum bimetal composite samples. After 360 the ship steel-aluminum bimetal composite samples. After the the 360° twisting test was applied to the the bimetal composite samples, no cracks or fractures in bonding the bonding interface of any of bimetal composite samples, no cracks or fractures werewere seenseen in the interface of any of the the composites. composites.

Figure Figure 14. 14. Macro Macro images images of of bimetal bimetal composite composite samples samples after after the the twisting twisting test. test.

No cracks or fractures occurred in the composite samples and although high strain-hardening No cracks or fractures occurred in the composite samples and although high strain-hardening levels were achieved, excessive cold deformation was seen in the bimetal composites due to the levels were achieved, excessive cold deformation was seen in the bimetal composites due to the explosive ratio and the deformation that was applied to the composites in the twisting test. The explosive ratio and the deformation that was applied to the composites in the twisting test. The twisting twisting test once again proved the bonding interface quality of the bimetal composite materials test once again proved the bonding interface quality of the bimetal composite materials produced. produced. It also showed that the composites were dependable and could be twisted and used under It also showed that the composites were dependable and could be twisted and used under service service conditions. Wang et al. [34] performed twisting tests in order to determine the joint quality of conditions. Wang et al. [34] performed twisting tests in order to determine the joint quality of copper/steel bimetal composites that were produced with explosive welding and reported that the copper/steel bimetal composites that were produced with explosive welding and reported that the interface strength was satisfactory and that no cracking had occurred in spite of the high degree of interface strength was satisfactory and that no cracking had occurred in spite of the high degree of deformation and hardening. deformation and hardening. 3.7. Microhardness Results Figure 15 shows results of the microhardness test that was applied to the ship steel-aluminum bimetal composite samples in order to determine the influences of different explosive ratios on the hardness values. When the hardness graph is examined, with increases in the explosive ratio, increases in the hardness values of the bimetal composite joining interface and its vicinity (~750 μm

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3.7. Microhardness Results Figure 15 shows results of the microhardness test that was applied to the ship steel-aluminum bimetal composite samples in order to determine the influences of different explosive ratios on the hardness values. When the hardness graph is examined, with increases in the explosive ratio, increases in the hardness values of the bimetal composite joining interface and its vicinity (~750 µm in ship steel/~500 µm in aluminum) were observed. The impact velocity of the plates increased at increasing explosive ratios, and as a result, the deformation levels increased. The increasing deformation levels subsequently increased the hardness values. Metals 2018, 8, x FOR PEER REVIEW 11 of 15

Figure 15. Hardness test results of ship steel-aluminum bimetal composite samples. Figure 15. Hardness test results of ship steel-aluminum bimetal composite samples.

When the hardness values of the bimetal composite sheets were examined, a significant increase When the hardness values the bimetal composite weresurfaces examined, a significant in hardness was seen near the of joining interface and on sheets the outer of the compositeincrease sheets, in hardness was seen near the joining interface and on the outer surfaces of the composite sheets, whereas the hardness values of the thick central areas of the sheets were nearly the same as those of whereas the hardness values of the thick central areas of the sheets were nearly the same as those the original materials. Furthermore, from the hardness value increases of the bimetal composite of the original materials. Furthermore, fromvalues the hardness value increases of the bimetalwere composite plates, it was understood that the hardness measured near the joining interface higher plates, it was understood that the hardness values measured near the joining interface were higher than the hardness values that were measured from the outer surfaces of the plates. In the explosive than the hardness values that werethe measured the outer surfaces of the plates. In the welding method used to produce bimetal from composite plates, the bonding interface andexplosive the outer welding method used to produce the bimetal composite plates, the bonding interface and theby outer surface of the plates are exposed to cold deformation due to the impact pressure sustained the surface of the plates are exposed to cold deformation due to the impact pressure sustained by the plates, dependent upon the explosive ratio. As understood from the microstructure tests that were plates, uponcomposite the explosive ratio.(Figure As understood from the microstructure tests were applieddependent to the bimetal samples 6), the deformation level decreased at that distances applied to the bimetal composite samples (Figure 6), the deformation level decreased at distances moving further away from the bonding interface, and the hardness decreased as a result. For moving further from thehardness bondingof interface, and decreased as aas result. Forat example, example, whilstaway the original ship steel is the ~140hardness HV, it was measured 176 HV the R = whilst the original hardness of ship steel is ~140 HV, it was measured as 176 HV at the R = 2 explosive 2 explosive ratio at a distance of 250 µ m (the closest distance to the bonding interface), 175 HV at a ratio at a of distance 250 µm distance thecenter bonding interface), distance 500 m,of~147 HV (the at theclosest thickest area attothe (2500 µ m), and175 171HV HVat ataadistance distance of of 500 HV the at the thickest area surface). at the center (2500 µm), and 171 HV at asame distance of 4900were µm 4900µm, m~147 (around ship steel outer For R = 2.5, these values (at the distances) (around theasship outer surface). For R =173 2.5,HV, these values (at the distances) measured 180 steel HV, 178 HV, 149 HV, and respectively. Thesame hardness profilewere wasmeasured similar to as 180 HV, 178 HV, 149 HV, and 173 HV, respectively. The hardness profile was similar to these results these results for the explosive ratios of R = 3 and R = 3.5. Likewise, it was found that the hardness for the explosive ratios of R = 3 and R = 3.5. Likewise, it was found that the hardness values measured values measured from the aluminum side of the bimetal composite samples increased at increasing from the aluminum side of the bimetal composite samples increased at increasing explosive explosive ratios. In addition, the hardness value decreased at distances moving further awayratios. from In addition, the hardness value decreased at distances moving further away from the bonding interface the bonding interface of the aluminum side of the bimetal composite material and was close to the of the aluminum side of the bimetal composite material wasofclose to the The original aluminum original aluminum hardness value (40 HV) at the thick and center the plate. hardness value hardness value (40 HV) at the thick center of the plate. The hardness value increased again at distances increased again at distances that were closer to the outer surface. that were closer the outer surface. Gülenç [35]toperformed hardness tests on Al/Cu bimetal composite plates he had produced via explosive welding and reported that the reason behind the increased hardness in the bonding interface was the cold deformation arising from the high-velocity collision of the explosion on the outer surface of the upper plate and the outer surface of the lower plate base material. This caused the hardness of the outer surface of the plates to increase. This increase in hardness in the bonding interface and outer surfaces of the plates was caused by the sudden shock wave, dependent upon on

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Gülenç [35] performed hardness tests on Al/Cu bimetal composite plates he had produced via explosive welding and reported that the reason behind the increased hardness in the bonding interface was the cold deformation arising from the high-velocity collision of the explosion on the outer surface of the upper plate and the outer surface of the lower plate base material. This caused the hardness of the outer surface of the plates to increase. This increase in hardness in the bonding interface and outer surfaces of the plates was caused by the sudden shock wave, dependent upon on the explosive ratio. Moreover, Gülenç found that the deformation depth dependent on the collision velocity was limited and that the hardness remained unchanged at the thick central areas of the plates. Various bimetal composites were produced by Fronczek et al. [36] (Ti/Al), Prasanthi et al. [37] (Mild Steel/Ti), and Saravanan et al. [38] (Al/Cu) using the explosive welding method and they reported parallel results following microhardness tests. Metals 2018, 8, x FOR PEER REVIEW

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3.8.Figure Neutral Spray Test Results 16Salt shows macro images of the composite samples after the NSS test performed in order to

determine the16 corrosion behavior of the samples in seawater. Figure shows macro images of the composite samples after the NSS test performed in order The images of the samples after the NSS tests show that the ship steel had suffered to determine the corrosion behavior of the samples in clearly seawater. corrosion to its of high After show 24 h, the corrosion Thedue images thechemical samples affinity after thewith NSSoxygen. tests clearly thatNSS the test shiprevealed steel had sufferedon thecorrosion ship steeldue side bimetallic corrosion notNSS observed on thecorrosion aluminum to of itsthe high chemical composites, affinity with while oxygen. After 24was h, the test revealed side. 48steel h, the NSS testbimetallic showed that the shipwhile steel side of thewas composites wason almost completely on After the ship side of the composites, corrosion not observed the aluminum side. After 48 h,the thealuminum NSS test showed thatretained the ship steel side of the compositesItwas completely corroded, while side still its corrosion resistance. canalmost be concluded from corroded, while the aluminum side stillof retained its corrosion resistance. It using can beexplosive concludedwelding from these NSS test results that the cladding aluminum on top of ship steel these NSS that thecorrosion cladding in of aaluminum top of ship steel using explosive welding protected thetest shipresults steel against seawater on environment. protected the ship steel against corrosion in a seawater environment. Kaya et al. [13] produced Grade A ship steel-AISI 2304 duplex stainless steel composite materials Kaya etwelding al. [13] produced Gradecorrosion A ship steel-AISI 2304and duplex stainless steel composite materials via explosive and applied tests (NSS potentiodynamic polarization) to the via explosive welding and applied corrosion tests (NSS and potentiodynamic polarization) to the composite specimens. The AISI 2304 was found to protect the Grade A plates against corrosion, composite specimens. The AISI 2304 was found to protect the Grade A plates against corrosion, especially in sea water. especially in sea water.

Figure the neutral neutralsalt saltspray spraytest. test. Figure16. 16.Macro Macroimages images after the

4. Conclusions 4. Conclusions The followingconclusions conclusionswere weremade made as as aa result the microstructural, The following result of of this thisstudy studyinvestigating investigating the microstructural, mechanical, and corrosion features of ship steel-aluminum bimetal composite materials that were mechanical, and corrosion features of ship steel-aluminum bimetal composite materials that were produced via explosive welding at different explosive ratios: produced via explosive welding at different explosive ratios: 

In the ship steel-aluminum bimetal composite samples, waving in the interface increased at increasing explosive ratios and in parallel with this, the wavelength and amplitude increased. In addition, the grains close to the bonding interface extended parallel to the explosion direction as a result of the sudden cold plastic deformation that occurred due to the pressure applied during the explosive welding. This effect gradually disappeared at distances moving further away from

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In the ship steel-aluminum bimetal composite samples, waving in the interface increased at increasing explosive ratios and in parallel with this, the wavelength and amplitude increased. In addition, the grains close to the bonding interface extended parallel to the explosion direction as a result of the sudden cold plastic deformation that occurred due to the pressure applied during the explosive welding. This effect gradually disappeared at distances moving further away from the interface. The SEM and EDS investigations on the ship steel-aluminum bimetal composite joining interface revealed that a flat interface was obtained at a low explosive ratio and no intermetallic formation was observed, but as the explosive ratio increased, a wavy structure was formed by mechanical interlocking at the interface and some intermetallic compounds (FeAl3 + αAl and α2 ) were formed. As a result of tensile-shear tests applied to the ship steel-aluminum bimetal composite samples, tensile-shear strength increased at increasing explosive ratios. In addition, no separation was present in the bonding interface of the composite samples. The SEM images of the fracture surfaces revealed ductile fractures having a matte and fibrous appearance. As a result of the notch impact test performed at room temperature, the impact toughness decreased due to increased deformation hardening at increasing explosive ratios. Additionally, cracking occurred in the ship steel (base plate) side of the ship steel-aluminum bimetal composites, and although bending was seen in the aluminum (cladding plate) side, no separation was present. The two-way bending tests performed by bending samples 180◦ revealed no visible cracks, fractures, or separation in the bonding interface of the bimetal composite samples that were produced at different explosive ratios. After the 360◦ twisting test was applied to the bimetal composite samples, no faults were seen in the bonding interface of any of the composites. The hardness test showed that the highest hardness value was measured at the bonding interface, followed by the outer surface of the plates (ship steel and aluminum) and the thick central areas of the plates. Moreover, the hardness values that were measured for the bimetal composite samples increased at increasing explosive ratios. As a result of salt spray tests, the aluminum cladded to the ship steel surface exhibited greater corrosion resistance when compared to that of the ship steel. In the microstructure studies applied to the ship steel-aluminum bimetal composite specimens, no unbonded areas were seen at the joining interface. After mechanical tests, no separation was observed at the joining interface, and after corrosion tests, no corrosion was found on the aluminum side of the joining. It can be stated that the R = 2 explosive ratio is the best choice for reducing deformation at the joining interface in the production of ship steel-aluminum bimetal composites.

Funding: This research received no external funding. Acknowledgments: I thank the MKE Barutsan Company (Turkey) for providing explosives and facilities for explosive cladding process. This research received no external funding. Conflicts of Interest: The author declare no conflict of interest.

References 1. 2. 3.

Kaya, Y.; Kahraman, N. An investigation into the explosive welding/cladding of grade a ship steel/AISI 316L austenitic stainless steel. Mater. Des. 2013, 52, 367–372. [CrossRef] Li, X.; Ma, H.; Shen, Z. Research on explosive welding of aluminum alloy to steel with dovetail grooves. Mater. Des. 2015, 87, 815–824. [CrossRef] Young, G.A.; Banker, J.G. Explosion welded, bi-metallic solutions to dissimilar metal joining. In Proceedings of the 13th Offshore Symposium, Houston, YX, USA, 24 February 2004; pp. 1–6.

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5. 6. 7. 8. 9. 10. 11. 12. 13.

14. 15. 16. 17. 18. 19. 20. 21.

22. 23. 24.

25.

26. 27.

14 of 15

Koschlig, M.; Veehmayer, M.; Raabe, D. Production of steel-light metal compounds with explosive metal cladding. In Proceedings of the 3rd International Conference on High Speed Forming, Dortmund, Germany, 11–12 March 2008; pp. 23–32. Wang, J.M.; Zhang, Y.A. A study on weldability of aluminum alloy-aluminum-steel transition joints. Adv. Mater. Res. 2013, 631, 713–716. [CrossRef] Tricarico, L.; Spina, R. Experimental investigation of laser beam welding of explosion-welded steel/ aluminum structural transition joints. Mater. Des. 2010, 31, 1981–1992. [CrossRef] Tricarico, L.; Spina, R.; Sorgente, D.; Brandizzi, M. Effects of heat treatments on mechanical properties of Fe/Al explosion-welded structural transition joints. Mater. Des. 2009, 30, 2693–2700. [CrossRef] Tricarico, L.; Spina, R. Mechanical strength of Fe/Al structural transition joints subject to thermal loading. Arch. Mater. Sci. Eng. 2009, 37, 85–93. Mousavi, S.A.A.; Barrett, L.M.; Al-Hassani, S.T.S. Explosive welding of metal plates. J. Mater. Process. Technol. 2008, 1–3, 224–239. [CrossRef] Guo, X.; Wang, H.; Liu, Z.; Wang, L.; Ma, F.; Tao, F. Interface and performance of clam steel/aluminum clad tube prepared by explosive bonding method. Int. J. Adv. Manuf. Technol. 2016, 82, 543–548. [CrossRef] Sun, X.-J.; Tao, J.; Guo, X.-Z. Bonding properties of interface in Fe/Al clad tube prepared by explosive welding. J. Trans. Nonferrous Met. Soc. China 2011, 21, 2175–2180. [CrossRef] Guo, X.; Tao, J.; Wang, W.; Li, H.; Wang, C. Effects of the inner mould material on the aluminium-316L stainless steel explosive clad pipe. Mater. Des. 2013, 49, 116–122. [CrossRef] Kaya, Y.; Kahraman, N.; Durgutlu, A.; Gülenç, B. Investigation of the microstructural, mechanical and corrosion properties of grade a ship steel-duplex stainless steel composites produced via explosive welding. Metall. Mater. Trans. A 2017, 48, 3721–3733. [CrossRef] Szachogluchowicz, I.; Sniezek, L.; Hutsaylyuk, W. Low cycle fatigue properties of AA2519–Ti6Al4V laminate bonded by explosion welding. Eng. Fail. Anal. 2016, 69, 77–87. [CrossRef] Miao, G.; Ma, H.; Shen, Z.; Yu, Y. Research on honeycomb structure explosives and double sided explosive cladding. Mater. Des. 2014, 63, 538–543. [CrossRef] Acarer, M.; Gülenç, B.; Fındık, F. The influence of some factors on steel/steel bonding quality on their characteristics of explosive welding joints. J. Mater. Sci. 2004, 39, 6457–6466. [CrossRef] Acarer, M.; Gülenç, B.; Fındık, F. Investigation of explosive welding parameters and their effects on microhardness and shear strength. Mater. Des. 2003, 24, 659–664. [CrossRef] Kahraman, N.; Gülenç, B.; Fındık, F. Joining of titanium/stainless steel by explosive welding and effect on interface. J. Mater. Process. Technol. 2005, 169, 127–133. [CrossRef] Yazdani, M.; Toroghinejad, M.R.; Hashemi, S.M. Investigation of microstructure and mechanical properties of St37 steel-Ck60 steel joints by explosive cladding. J. Mater. Eng. Perform. 2015, 24, 4032–4043. [CrossRef] Durgutlu, A.; Gülenç, B.; Fındık, F. Examination of copper/stainless steel joints formed by explosive welding. Mater. Des. 2005, 26, 497–507. [CrossRef] Chu, Q.L.; Zhang, M.; Li, J.H.; Jin, Q.; Fan, Q.Y.; Xie, W.W.; Luo, H.; Bi, Z.Y. Experimental investigation of explosion-welded Cp-Ti/Q345 bimetallic sheet filled with Cu/V based flux-cored wire. Mater. Des. 2015, 67, 606–614. [CrossRef] Fındık, F. Recent developments in explosive welding. Mater. Des. 2011, 32, 1081–1093. [CrossRef] Zhang, L.J.; Pei, Q.; Zhang, J.X.; Bi, Z.Y.; Li, P.C. Study on the microstructure and mechanical properties of explosive welded 2205/X65 bimetallic sheet. Mater. Des. 2014, 64, 462–476. [CrossRef] Mastanaiah, P.; Madhusudhan Reddy, G.; Satya Prasad, K.; Murthy, C.V.S. An investigation on microstructures and mechanical properties of explosive cladded C103 niobium alloy over C263 nimonic alloy. J. Mater. Process. Technol. 2014, 214, 2316–2324. [CrossRef] Hoseini Athar, M.M.; Tolaminejad, B. Weldability window and the effect of interface morphology on the properties of Al/Cu/Al laminated composites fabricated by explosive welding. Mater. Des. 2015, 86, 516–525. [CrossRef] Mazar Atabaki, M.; Nikodinovski, M.; Chenier, P.; Ma, J.; Harooni, M.; Kovacevic, R. Welding of aluminum alloys to steels: An overview. J. Manuf. Sci. Prod. 2014, 14, 59–78. [CrossRef] Xie, M.X.; Zhang, L.J.; Zhang, G.F.; Zhang, J.X.; Bi, Z.Y.; Li, P.C. Microstructure and mechanical properties of Cp-Ti/X65 bimetallic sheets fabricated by explosive welding and hot rolling. Mater. Des. 2015, 87, 181–197. [CrossRef]

Metals 2018, 8, 544

28. 29. 30. 31. 32. 33. 34. 35. 36.

37. 38.

15 of 15

Asemabadi, M. Sedighi, M.; Honarpisheh, M. Investigation of cold rolling influence on the mechanical properties of explosive-welded Al/Cu bimetal. Mater. Sci. Eng. A 2012, 558, 144–149. [CrossRef] Loureiro, A.; Mendes, R.; Ribeiro, J.B.; Leal, M.; Galvao, I. Effect of explosive mixture on quality of explosive welds of copper to aluminium. Mater. Des. 2016, 95, 256–267. [CrossRef] Kaçar, R.; Acarer, M. An investigation on the explosive cladding of 316L stainless steel-DIN-P355GH steel. J. Mater. Process. Tech. 2004, 152, 91–96. [CrossRef] ˙ Gülenç, B.; Kaya, Y.; Durgutlu, A.; Gülenç, I.T.; Yıldırım, M.S.; Kahraman, N. Production of wire reinforced composite materials through explosive welding. Arch. Civ. Mech. Eng. 2016, 16, 1–8. [CrossRef] Xia, H.B.; Wang, S.G.; Ben, H.F. Microstructure and mechanical properties of Ti/Al explosive cladding. Mater. Des. 2014, 56, 1014–1019. [CrossRef] Kahraman, N.; Gülenç, B.; Fındık, F. Corrosion and mechanical-microstructural aspects of dissimilar joints of Ti-6Al-4V and Al plates. Int. J. Impact Eng. 2007, 34, 1423–1432. [CrossRef] Wang, Y.; Beom, H.G.; Sun, M.; Lin, S. Numerical simulation of explosive welding using the material point method. Int. J. Impact Eng. 2011, 38, 51–60. [CrossRef] Gülenç, B. Investigation of interface properties and weldability of aluminum and copper plates by explosive welding method. Mater. Des. 2008, 29, 275–278. [CrossRef] Fronczek, D.M.; Wojewoda-Budka, J.; Chulist, R.; Sypien, A.; Korneva, A.; Szulc, Z.; Schell, N.; Zieba, P. Structural properties of Ti/Al clads manufactured by explosive welding and annealing. Mater. Des. 2016, 91, 80–89. [CrossRef] Prasanthi, T.N.; Sudha Ravikirana, C.; Saroja, S. explosive cladding and post-weld heat treatment of mild steel and titanium. Mater. Des. 2016, 93, 180–193. [CrossRef] Saravanan, S.; Raghukandan, K.; Hokamoto, K. Improved microstructure and mechanical properties of dissimilar explosive cladding by means of interlayer technique. Arch. Civ. Mech. Eng. 2016, 16, 563–568. [CrossRef] © 2018 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).