Effect of Rotation Speed on the Microstructure and Mechanical Properties of Friction-Stir-Welded CuSn6 Tin Bronze

Four-mm-thick CuSn6 tin bronze plates were friction stir welded at a constant tool traverse speed of 100mmmin(-1). Favorable joints could be obtained with rotation speeds ranging from 600 to 1000revmin(-1), and groove was found on the surface of the joint under 400revmin(-1). The microstructure of the weld nugget zone was characterized by equiaxed recrystallized grains with heterogeneity along the thickness direction. Moreover, the grain size of the thermo-mechanically affected zone and stir zone increased with the increase in rotation speed. Hardness of the stir zone was higher than that of other zones due to microstructural refinement. There was little change in tensile properties of the defect-free welded joints. During tensile test, all of the defect-free joints were fractured at heat-affected zone with typical plastic fracture.