Feasibility study of friction stir welding of 6061-T6 aluminium alloy with AISI 1018 steel

The present work demonstrates that friction stir welding (FSW) is a feasible route for joining 6061 aluminium (Al) alloy to AISI 1018 steel. The weld has a good weld quality and is free of cracks and porosity. The tensile failure happened at the boundary between the nugget and thermomechanically affected zone of the base Al alloy, indicating that the weld has a higher joining strength. Despite the fact that the hardness fluctuates strongly within the nugget, the average hardness of the nugget is substantially higher than that of the base Al alloy. During FSW, localized melting of the Al alloy in the nugget occurred, and the molten Al alloy reacted strongly with steel pieces spread through the nugget, which resulted in the formation of the Al-Fe intermetallic compounds, Al13Fe4 and Al5Fe2. The nugget consists of secondary phases including coarse steel pieces and Al-Fe intermetallic compounds, and an Al alloy matrix. These secondary phases contribute to the hardness of the weld.