Mechanical And Microstructure Characterization Of Oil Treated Aluminium Alloy 7075

Moamad Izzudin, Abdul Hamit (2010) Mechanical And Microstructure Characterization Of Oil Treated Aluminium Alloy 7075. Project Report. UTeM, Melaka Malaysia. (Submitted)

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Abstract

The objectives of this research are to investigate the effect of retrogression and re-aging (RRA) process on microstructure, corrosion susceptibility (both in applied force (SCC) and without applied force condition) and mechanical properties of aluminum alloy 7075 when performed by oil retrogression. In this research, aluminum alloy 7075 have used as raw material of sample according to the highest attainable strength levels of all forged alloys and is capable of good stress corrosion resistance. In this sample preparation, aluminum alloy 7075 was have solution heat treatment by heated samples in the furnace to the temperature of 470 °C for one hour and followed by water quenching at room temperature. The quenched samples have preheated for age hardening at 120 °C for 24 hours. Then, the RRA process has applied to the sample in the T6 condition to improve its stress corrosion cracking (SCC) by immerse it into oil. Temperature and time is the variable for the RRA process. Samples that have done with oil retrogression then have re-aging at 120 °C for 24 hours. Result shows the samples that perform with oil retrogression at 165oC for 10 minutes have highest attainable mechanical properties approximate the T6 strength compared to others parameters of sample. With increasing parameters of time and temperature, the mechanical strength gradually decreases to the values close to the T73 tempers. Microstructures of the treated aluminium alloy 7075 majorly influence the mechanical properties of the specimens. Formation of the η phase that presents as strengthening precipitates contributes most to strength of the samples. Comparison to the corrosion susceptibility of the treated aluminium alloy 7075, the results showed SCC susceptibility can be enhanced by RRA treatment. Retrogression and re-aging (RRA) treatment shows able to produce combination of T6 and T73 properties by make reduction of T6 strength to improve SCC susceptibility approached T73 tempers.

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