Enhancement of microstructure, micro-texture, and mechanical properties of Al6061 friction stir welds using the developed static shoulder welding tool

Abstract

Dissolution of strengthening precipitates and grain coarsening are the key factors that dictate the mechanical properties of heat-treatable aluminium alloys. In this study, a feasible method of static shoulder friction stir welding (SSFSW) is used to reduce these adverse effects. A novel static shoulder friction welding tool is developed here in this study by incorporating rotating and non-rotating shoulders in a single tool. The effectiveness of the tool was evaluated by welding Al6061 plates under various conditions, such as conventional friction stir welding (CFSW), underwater friction stir welding (UWFSW), and SSFSW. The evolution of crystallographic texture and microstructural changes during the process is studied using electron back scattered diffraction and transmission electron microscopy. The results showed that SSFSW reduced grain size by 37% compared to UWFSW at the centre of the stir zone and increased the yield strength by 22.8% compared to CFSW. In addition, SSFSW showed a strong presence of γ-fibre, indicating improved formability and a 7.2% improvement in joint efficiency in terms of ultimate tensile strength due to a higher fraction of precipitates and higher dislocation density.