LAUSR

Abstract Effects of underwater friction stir welding tool pin profiles were studied on mechanical properties of AA5182 alloy and St-12 steel dissimilar joint. For this purpose, frustum, triangle, cubic, and hexagonal pin profiles were selected. Thermal history, microstructure analysis, tensile strength, and hardness of joint lines were assessed. The obtained results indicated that due to the high cooling rate of water environment conditions, the presence of edges in the tool pin shape (triangle, cubic, and hexagonal) improves internal material flow. Also, edged pin profiles increase the generation of frictional heat, the thickness of Intermetallic Compounds (IMC), and mechanical interlocking at base materials' interface. The hexagonal pin profile had the most significant favourable influence on the aluminium-steel joint properties among selected tool profiles. The chemical composition of IMCs at the materials interface was FeAl3 and Fe2Al5, and the thickest IMC was formed near 6.5 μm. According to the results, the joint's highest tensile strength was ~69% of aluminium alloy strength, which was obtained with a hexagonal pin profile.