THE INFLUENCE OF SULPHURIC ACID

JOURNAL Of NUCLEAR And Related TECHNOLOGIES, Volume 6, No. 1, Special Edition, 2009

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THE INFLUENCE OF SULPHURIC ACID CONCENTRATION ON HARD ANODISING PROCESS ON POWDER METALLURGY Al-Mg Mohd Nazree Derman, Mohd Nasuha Abd Halim and Shaiful Rizam Shamsudin School of Materials Engineering, Universiti Malaysia Perlis, Kompleks Pusat Pengajian Jejawi 2 Taman Muhibbah,02600 Arau, Perlis

ABSTRACT The hardcoat anodising process was done by using different concentration of H2SO4 from 0% to 20%. The 90 volt of anodising process was applied by using Al foil as cathode materials. The surface changes on PM Al-Mg resulted by hardcoat anodising was characterised by XRD measured. Surface hardness was measured by Micro-Vickers hardness machine. The experiment found different XRD pattern between anodised PM Al-Mg samples. The study was found by that the optimum value for H2SO4 concentration was 15 % H2SO4 and result 26 μm thickness, 5.07% of mass changes and HVN 105.4 hardness. The hardcoat anodising was affected to the XRD pattern for PM Al-Mg.

ABSTRAK Penganodan salutan keras menggunakan kepekatan H2SO4 yang berbeza dari 0% hingga 20%. Proses penganodan 90 V ini menggunakan kepingan Al sebagai bahan katod. Perubahan permukaan pada PM Al-Mg terhasil daripada proses penganodan salutan keras dicirikan oleh pengukuran XRD. Kekerasan permukaan diukur oleh mesin kekerasan mikro Vickers. Eksperimen mendapati corak XRD yang berbeza di antara sample-sampel PM Al-Mg. Kajian mendapati bahawa nilai optimum untuk kepekatan H2SO4 adalah 15% H2SO4 menghasilkan ketebalan 26μm , 5.07% perubahan jisim dan kekerasan HVN 105.4. Penganodan salutan keras telah memberi kesan kepada corak XRD bagi PM Al-Mg Keywords: Powder metallurgy, anodising, aluminium dan magnesium

INTRODUCTION The powder metallurgy (PM) route for metal manufacturing offer some advantages compared with casting. The main advantage is the low manufacturing temperature that avoids strong interfacial reaction and minimizing the undesired reactions between the matrix and the reinforcement. Aluminum and magnesium are used because of their unique combination of good corrosion resistance, low electrical resistance and excellent mechanical properties (Drozen and Amir 2003). Hard coat anodizing process is one of the anodizing process which is provides hard surface on the materials. Hard coat anodizing was the most widely used in industrial. In the hard coat anodizing process, it uses an electrolyte cell with H2SO4 as a solution. The solution and electric field used in hard coat anodizing process will determine the thickness of the oxide layers (Wood et al, 1970). However, the metallurgical factor such alloying element and microstructure properties in PM Al-Mg contributes the different result in anodising in term of oxide film thickness and surface 224


hardening. The objective of this experimental was to determine the contribution of H2SO4 concentration for oxide layer and its properties

EXPERIMENTAL METHODS PM Al-Mg was fabricated by powder metallurgy method. The flaky aluminium powder was wet mixed with 0.2%wt magnesium and ethanol in ball mill jar. The ball powder ratio used was 10:1 ratio. The mixing was done at 300 rpm for 1 h. The mixture was dried at 70 oC in vacuum oven for 3 h. Mixed powder was compacted at 200 MPa and it was sintered in argon gas at 610 o C. Hard coat anodising process was carried out in 0-3°C. Output voltage in this process was 90 V. This process was using four different concentrations which were 5, 10, 15 and 20 % H2SO4 for 60 minutes. The coating was characterised by the mass changes, thickness and hardness and XRD pattern by using digital balance, Olympus BX41M Metallurgical microscope, HM-114 Mitutoyo micro hardness tester and Shimadzu XRD 2000 respectively.

RESULTS AND DISCUSSION Mass Changes and thickness coating Figure 1 shows the percentage of mass changes and thickness for 60 minutes of anodizing PM Al-Mg with different H2SO4 concentration (from 5% H2SO4 to 20% H2SO4). The percentage of coating mass changes increased with increasing H2SO4 concentration. The bigger increasing mass changes are indicate from 5% H2SO4 to 15% H2SO4 and reduced after 15% H2SO4. However, the coating thickness for 5% and 10% are almost 15 μm and suddenly increased to 26 μm for 15% H2SO4 and small increase to 28.96 μm for 20% H2SO4. The hardcoat anodizing with 5% H2SO4 shows the lower coating thickness (14.62 μm) and percentage of mass changes (1.01%) compared to the others H2SO4 concentration. The 20% H2SO4 shows the maximum thickness (28.96 μm) meanwhile 15% H2SO4 indicates the bigger changes in mass coating (5.07%). Anodising thickness was depends on anodizing conditions is in agreement with familiar properties of anodised films. The amount of aluminium oxidised or converted into oxide (Al2O3) during anodising and the thickness of the anodised oxide layer has been determined gravimetrically by mass changes, as shown in Fig 2. Conversion of aluminium is determined by the anodizing time and the current density and increased conversion is reported with increased time and/or current density. Morphology and thickness of the anodised oxide film, however, also depends on the anodising voltage, the temperature and the composition of the electrolyte used (Drozan and Amir, 2003).

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6.0

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Figure 1: The influence of H2SO4 on coating mass changes and thickness in anodizing process.

Al

Al2O3

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(a) 20 % H2SO4

(b) 15 % H2SO4

Al2O3

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Al Al

(c) 10 % H2SO4

(d) 5 % H2SO4

Figure 2: Anodising thickness measured by metallurgical microscope

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Coating Hardness Figure 3 shows hardness value for 60 minutes of anodised PM Al-Mg. The increasing of hardness value was influenced by H2SO4 concentration. The maximum hardness of anodised PM Al-Mg was HVN 108.64 indicated by 20% H2SO4. HVN 47.66 was smallest hardness obtained by 5% H2SO4. 10 and 15 % H2SO4 show HVN 62.56 and HVN 67.19. The 15% H2SO4 shows the highest hardness compared to 5% H2SO4. These hardness values influenced by coating properties like thickness and mass changes resulted by different H2SO4 concentration.

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Microhardness (HV0.3 kg)

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10 15 Sulphuric Acid Concentration (%)

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Figure 3: The hardness distribution of anodized PM Al-Mg. XRD Analysis Figure 4 shows the XRD pattern of PM Al-Mg and anodized PM Al-Mg with different H2SO4 concentrations. There were no significant changes on XRD peak. However, the intensity peaks of anodised PM Al-Mg were decreases with increasing H2SO4 concentration. The showed that all concentration of H2SO4 consisting of a mixture alpha and gamma Al2O3. The increasing H2SO4 concentration was reduced the peak size of XRD in range 10 to 20 degree of 2-theta. The oxide film also found in non anodised PM Al-Mg but it neutrally form compared to anodised samples. XRD pattern also detected Al and Mg because hardcoat anodising films are porous and very thin. Therefore, Al and Mg also were indicating in XRD pattern. According to Nie et al (1999) oxide film created in Al surface in anodising process consisting aluminium oxide and hydrate.

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Relative Intensity(a.u)

PM Al-Mg

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10%H2SO4 15%H2SO4 20%H2SO4 10

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Figure 4: XRD analysis for PM Al-Mg and anodised PM Al-Mg with different H2SO4 concentration. From that observation, Thickness and mass coating have relationship to influence hardness properties of hardcoat anodising PM Al-Mg. The H2SO4 concentration was important factor to enhance mechanical and physical properties. The absence of oxide film which detected by XRD pattern also influences the hardness and coating thickness and mass of hardcoat anodised PM Al-Mg. PM Al-Mg can coat by using hardcoat anodising process using 15wt % H2SO4 because it can give the optimum result in thickness and hardness. The presence 0.2wt% Mg in PM Al is not affected to hardcoat anodising but it can enhance the hardness. These resulted also share by Drojan and Emir (2003) and Nazree et al (2007). They found that 15% H2SO4 show the optimum result for coated oxide film forming. However, in this study, the 90 V in the process condition can improve coating hardness and thickness.

CONCLUSION The influence of H2SO4 on hardocat anodising process of PM Al-Mg was investigated. The hardcoat anodizing was successfully coated on a PM Al-Mg. The optimum value for H2SO4 concentration was 15 % H2SO4 and result 26 μm thickness, 5.07 % of mass changes and HVN 105.4 hardness. The XRD detect the changes of XRD relative intensity on PM Al-Mg which indicate that hardcoat anodising can influence the X-ray diffraction on PM Al-Mg.

ACKNOWLEDGMENTS The authors acknowledge Universiti Malaysia Perlis (UniMAP) and Ministry of Higher Education Malaysia for providing fundamental research grant scheme (9003-00047) for financial support that enable production of this articles.

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REFERENCES Drozen D.J and Amir Z.M (2003), Anodising of inner surface of long and small-bore Al tube, Surface and Coating Technology, 173;183-191 Mohd Nazree D, Zainal A.A., Luay B.H and Nurulakmal M.S.(2007), Study of anodized PM Aluminium matrix composite reinforced with 15wt% SaffilTM alumina Short fibre, J Nuclear and Related Technology, Vol.4, Special Edition,1&2;155-158. Sundrica, J. (1981). Determination of the Optimal rotational Speed for Powder Mixing, Inter J. Powder Met. Powder Tech, vol.17: 291-294 Too,J.R., Fan,L.T. and Lai, F.S.(1978) Mixture and Mixing of Multicomponent Solid Particles A Review.” J. Powder Bulk Solids Tech., vol. 2: 2-8 Wood, G. C. and O´ Sullivan, J. P.,(1970) The Anodizing of Aluminum in Sulphate Solutions, Electrochemica Acto, Vol. 15,:1865 1876.

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