Effect of post-welding heat treatment on mechanical properties of butt FSW joints in high strength aluminium alloys

Abstract

The friction stir welding (FSW) is a solid state welding process for joining two dissimilar metals using non consumable tools. This paper deals with experimental investigation on the effect of post welded heat treatment on mechanical properties of butt joint using FSW in aluminium alloys 2024 T6 (soft metal) and 7075 T6 (hard metal). In the post weld treated joint, the increase in hardness homogeneity is analysed in the nugget zone along the profile using micro hardness profile measurement. When the hardness homogeneity is attained, fracture occurs in nugget zone. The butt FSW joint after post welding heat treatment at low temperatures (200°C and 300°C) have tensile properties comparable with the FSW joints and fracture occurs in base metal 7075 T6. In 50% of FSW joints, deformation occurs after heat treatment at low temperature and also failure occurs inside stir zone. This work reveals that the progressive changes in the grain size and morphology in higher temperature post weld heat treated joint owing to abnormal grain growth (AGG) in the stir zone.