Effect of tool pin profile on microstructure and mechanical properties of friction stir welded pure copper joints

In the present study, the effect of tool pin profile on microstructure and mechanical properties of friction stir welded pure copper joints were investigated. Two different tools with threaded cylindrical and square pin profiles were used to fabricate the joints at constant rotation rate of 600 rpm and traverse speed of 75 mm/min. Four K-type thermocouples were used to record the temperature histories of samples during FSW. Microstructure features of the joints were characterized by optical microscopy and the obtained images were quantified using image analysis technique. Tension test and Vickers hardness measurements were also performed to characterize the mechanical properties of the joints. Obtained results showed that sample welded using square pin profile had finer recrystallized grain structure and higher mechanical properties relative to sample welded by threaded cylindrical one. These results were attributed to higher eccentricity of the square pin profile and its pulsation effect which led to higher degree of plastic deformation and higher heat input into the joints.