Effect of tool offset on microstructure and mechanical properties of dissimilar copper-brass friction stir welding

This study has investigated the effect of tool offset on the mechanical behavior and microstructure of dissimilar copper and brass joints by friction stir welding (FSW). In this regard, the FSW method was used for joint with three different tool offset positions, namely center line (no offset), the copper side, and the brass alloy side. Microstructure and fracture surfaces of the specimens were examined by optical (OM) and scanning electron microscopies (SEM), respectively. Tensile, micro-hardness and bending tests were also utilized to evaluate the joints mechanical behavior. The results showed that an onion ring-shaped zone was formed with the tool offset towards the copper side, but this zone was not observed with the tool offset towards the brass alloy side. In addition, compared with the tool without offset, the tensile strength with the tool offset to copper side of 1 mm (Cu+1) increased by 33.33% and with the tool offset to brass alloy side of 1 mm (Brass+1) increased by 57.47%. The results of bending test showed that in the Brass+1 specimen, bending strength increased by approximately 5% compared with the specimen without offset. Finally, it was found that the best mechanical and microstructural properties were obtained by the tool offset of 1 mm towards the brass alloy side.