Effect of Tool Pin Profiles on the Weldment of AA6061-T6 Friction Stir Welded Plate

Friction stir welding (FSW) is a solid state welding in which a rotating non-consumable tool with pin and shoulder is plunged into the joint between workpiece and traverse along the joint, and generates heats from the friction to weld the workpiece. FSW is capable to weld hard-to-weld metal such as aluminium alloy which commonly used in lightweight construction. Since lightweight construction is in high demands nowadays, it is necessary to carry out research on FSW of aluminium alloy. In addition, tool geometry play vital role in formation of FSW joint. The potential variation in tool geometry is virtually infinite, considering pin and shoulder related to dimension. Thus, the main focus of this study is to investigate the effect of tool pin profile on the microstructure and hardness of friction stir welded AA6061-T6 plate. Five different types of tool pin profile including straight cylindrical, threaded cylindrical, tapered cylindrical, square and triangle are selected for this study. Heat treatment is performed on the tools fabricated to improve the hardness, resistance to thermal fatigue and wear. Microstructural analysis and Rockwell hardness, B scale test are performed for the purpose to investigate the microstructure and hardness on the stirred zone of AA6061-T6 FSW joint. The result shows that square pin profiled tool produces finer grain on the stirred zone and in turn yields higher hardness. Tool with flat faces has higher stirring action during FSW and result in producing joint with fine grain and high hardness.