The effect of SiC particles on the microstructure and mechanical properties of friction stir welded pure copper joints

The SiC particles with mean size of 5 μm were introduced into the pure Cu joints during the friction stir welding process. After one pass processing, the distribution of SiC particle is not uniform and some pores formed around the aggregation of SiC particles. However, the particle distribution became rather uniform after two passes processing and the previous pores can be refilled. In addition, banded structure consisting of particle-rich and particle-free region can be observed in the stir zone. The particle-rich region has an average grain size of less than 2 μm, much smaller than that of about 8 μm in the particle-free region. Microstructural observation confirmed that the SiC particles can act as the heterogeneous nucleation site in the dynamic recrystallization of Cu grains. The SiC dispersed Cu joints exhibit a Vickers hardness of 110 HV, much higher than 70 HV in the stir zone without SiC particles.