Influence of tool shoulder end features on friction stir weld characteristics of Al-Mg-Si alloy

In the present study, the tool shoulder end features such as concentric circle shoulder tool (TCC), ridge shoulder tool (TR), knurling shoulder tool (TK), and scroll shoulder tool (TS) were designed, and their effect on weld size, vertical force, temperature distribution, and material flow was investigated during friction stir welding (FSW) of Al-Mg-Si alloy. The vertical force, tool torque, and temperature during the welds were measured and compared for all the tools. The deformed marker material was used to analyze the material flow caused by the shoulder and pin. The experimental results show that the welds with shoulder end featured tools of smaller shoulder diameter (ϕ18mm)were comparable with the welds with plane shoulder tool (TP) of larger shoulder diameter (ϕ21mm) in the aspects of temperature and weld strength with reduced weld size. At initial stage, the plasticized material, beneath the tool shoulder, moves from advancing side (AS) to retreating side (RS) whereas the material around the pin moves from RS to AS. Overall, the welds produced with the proposed tool shoulder end features achieved lower vertical force, higher temperature, and minimum/no flash compared to TP of equal/higher shoulder diameter. The welds produced with TR resulted in better mechanical properties with lower vertical force, i.e., approximately 36% than that of (TP)21 tool and the hardness of weld zone is at a value of 65–78 HV0.1.