Influence of pre-weld temper conditions of base metal on microstructure and mechanical properties of friction stir weld joints of Al-Zn-Mg alloy AA7039

Friction stir welding is considered as one of the most significant development in the field of joining technologies. The present work is aimed to study the effect of initial temper conditions, viz. T6, W, and O of AA 7039 aluminum alloy, on microstructure, hardness and tensile properties of friction stir welds. It was observed that pre-weld temper condition had paramount influence on microstructure, mechanical properties, and fracture locations of welded joints. The highest and lowest tensile properties were exhibited by the friction stir weld joints of alloy in T6 and O temper respectively. The weld nugget of FSW joints developed using base metal in T6 and W temper conditions was found softer than the respective base metals while reverse trend was observed in case of joint produced using alloy in O temper condition. Fracture location shifts from base metal to weld nugget or heat affected zone with change in temper condition of the base alloy.