Effect of Scandium on Homogenization Treatment and Friction Stir Processing on Mechanical Properties of 7075 Aluminium Alloy Prepared by Foundry Route

Abstract

The aluminium alloy (7075 series) with minor scandium addition prepared by foundry route, was subjected to homogenization treatment at different temperature from 300 to 500°C for 8h and also multi-pass friction stir processing (MP-FSP) was performed to improve surface properties of cast aluminium alloy. The effect of minor scandium (0.33wt.%) on the microstructure and mechanical properties of prepared alloy was investigated using optical microscopy, SEM, FESEM, XRD, TEM, Vicker's hardness and tensile test. The homogenized microstructure was obtained showing fine grains because homogenization of cast structure and dispersion of second-phase particles also occur. The Al-Zn-Mg alloy with high strength, good corrosion resistance and good welding property is used widely in various industrial applications. In addition of Sc to increase the strength mainly comes from fine grain strengthening, substructure strengthening and precipitation strengthening caused by Al3(Sc) and MgZn2 particles. These particles are formed during homogenization treatment of cast aluminium alloy and it has great influence on precipitation behaviour of Al3(Sc) particles.