An investigation of the effect of auxiliary pins on mechanical properties of friction stir welded AA2024-T351

In this paper, novel friction stir welding tools in terms of design and geometry were introduced and fabricated to improve the mechanical properties of aluminum 2024-T351 friction stir welded joints. The proposed tools had auxiliary pins in addition to their central pin. Seven tools with different auxiliary pins and different pins offsets were used to fabricate FSW samples. Then, the tensile properties and micro-hardness of joints were examined. Maximum temperature values at different regions of welded samples and their shapes were deliberated using Coupled Eulerian–Lagrangian technique via numerical simulation of the FSW process. Tools with only one auxiliary pin resulted in higher mechanical properties compared to those with two auxiliary pins. Specifically, the tool with one auxiliary pin and a 7 mm offset had the most significant tensile strength value. These joints strength and ductility efficiencies to the base metal were 82.3% and 93.3%, respectively. However, tools with two auxiliary pins caused extreme and non-controlled plastic flow and material exiting from the top of the workpiece, resulting in lower mechanical properties. Also, it was found that auxiliary pin offsetting was the dominant factor in hardness variations in the stirred zone. Further, the minor offset generated the maximum temperature in the SZ among the tools with one auxiliary pin.