Evolution of the Microstructure and Strength in the Nugget Zone of Friction Stir Welded SiCp/Al–Cu–Mg Composite

A 6 mm-thick SiCp/2009Al composite plate was successfully joined by friction stir welding (FSW) using an ultra-hard material tool to investigate the evolution of the microstructure and the strength in the nugget zone (NZ). While some SiC particles were broken up during FSW, most of them rotated in the matrix. Large compound particles on the interfaces were broken off during FSW, whereas the amorphous layer and small compound particles remained on the interfaces. The dynamically recrystallized Al grains nucleated on the surface of fractured SiC particles during FSW, forming nano-sized grains around the SiC particles. The yield strength of the NZ decreased slightly due to the variation in the size, shape, and distribution of the SiC particles. The clean interfaces were beneficial to the load transfer between SiC particles and Al matrix and then increased the ultimate tensile strength of the NZ.