Microstructure evolution and mechanical properties on friction stir welding of SiCp/Al composites

In this study, the joining experiment of SiCp/Al composites with 4 mm thickness was carried out, and the effects of different tool rotational speeds (600, 1000 and 1400 rpm) on the microstructure evolution and mechanical properties of joint were studied. The results show that the rotation speed has a significant impact on the microstructure of the weld nugget (WN). The aluminium matrix forms a fine equiaxed crystal structure in WN. As the rise of the rotational speed from 600 to 1400 rpm, the grain size of WN decreased from 6.9 to 2.3 μm. Compared with the base material, the microhardness of the nugget zone was higher. As the rise of rotational speed, the maximum microhardness value increased. The ultimate tensile strength (UTS) of joints decreased with the increase of rotational speed and can reach 95.9% of the base material at 600 rpm. The failure modes of friction stir welding (FSW) joints are mainly ductile failure and SiC particle fracture.