Investigation into the effect of post weld heat treatment on microstructure and mechanical properties of friction stir welded AA6061 and AA7075 aluminium alloy plates

Physical and mechanical properties such as excellent corrosion resistance, low density and high formability are the most important factors determining the wide-spread use of a structural material. Among all metallic materials Al-alloys are used in a wide range of application areas in transportation industry where fuel consumption is very vital, due to their low density, high formability, and excellent corrosion behaviour.Al-alloys, which exhibit several difficulties in fusion welding, can be joined by newly developed solid state joining method namely friction stir welding (FSW) without any difficulties. However, the problem of loss of strength in the joint region is also encountered in FSW of precipitation-hardened Al-alloys as the case in fusion welding although the loss of strength is less pronounced. Although this joining process is currently used in joining of Al-alloys in practice there is a limited amount of work aiming at eliminating or decreasing the problem of loss of strength in the joint area including post weld heat treatment. Thus, there is certainly a need for conducting studies to determine the effect of post weld heat treatment on the joint performance of Al-alloys, particularly age-hardened grades.In this study, similar joints are produced by FSW on two different Al-alloys plates, namely highly corrosion resistant AA6061 and high strength AA7075, in both O and T6 temper conditions and the effect of post weld heat treatment on these joints is investigated. Firstly, a parametric study is conducted to determine the optimum welding parameters for each plate and the effect of temper condition on friction stir weldability of these two Al-alloys plates. The effect of post weld heat treatment on the weld performance of the joints produced with the predetermined optimum weld parameters is then investigated and the results obtained are discussed.