INFLUENCE OF FRICTION STIR PROCESSING ON MECHANICAL AND CORROSION PERFORMANCE OF Al ALLOYS

Abstract

Friction stir processing (FSP) is an effective solid state surface modification technique used to improve the surface properties of metallic systems like aluminium, and titanium using two approaches a) structural modification of near surface layers without change in composition and b) structural modification olnear surface layers coupled with change in composition. In present work, FSP of AA 7039 and as cast Al-17Si-0.5Mg was carried out. AA7039 is an Al-Zn-Mg based 7000 series alloy which is heat treatable and contains non copper, medium strength and containing Mg with Zn to form hard intermetallic phases to improve mechanical properties. Due to light weight AA7039 is using in engineering application. Al- I7Si-0.5Mg alloy commercially uses for production of engine blocks due to their high strength over weight ratio. Friction stir processing of 5 mm thick plates of both alloys was carried using conical shape pin. An overlap of 50% was used for modifying the surfaces. Modified surfaces were characterised in respect of macrostructure, microstructure, hardness and tensile properties. Immersion corrosion test and adhesive wear test also performed for comparison between base material and friction stir processed material. It was observed that FSP of AA 7039 alloy refines the microstructure and improves the ductility (%elongation) however tensile strength and hardness are adversely affected. Huge grain refinement was caused by the friction stir processing. Hardness has been found to be affected by number of passes during FSP. Multipass FSP was showing more hardness than the single pass. Solutionizing of the multipass friction stir processed AA7039 was carried at five different temperatures. Abnormal grain growth was observed at highest temperature (500 °C). Solutionizing followed by the water quenching and natural aging at room temperature. The wear resistance of the as cast Al-17Si-0.5Mg alloy was increased after FSP. As normal load is increasing, the wear rate was also increased.