An investigation of microstructure, wear and corrosion resistance of AZ31B-SiO2-graphite hybrid surface composite produced by friction stir processing

Abstract

Magnesium-based hybrid composites are light and have better mechanical and tribological properties than magnesium. In this research, AZ31B-SiO2-graphite hybrid surface composite was produced by multipass friction stir processing (FSP). The effect of FSP passes on microstructure, microhardness, wear resistance, and corrosion resistance of the composite was investigated and compared with friction stir processed (FSPed) AZ31B and as-received AZ31B. The results indicated that after 4 passes, SiO2 and graphite particles properly dispersed in the microstructure and grain growth was restricted due to the pinning effect of these particles; therefore, the mean grain size of the composite decreased by 80% compared with as-received AZ31B. The microhardness of the composite increased about 18% compared with as-received AZ31B and microhardness variation decreased in the stir zone, which indicates more homogeneity in grain size and particle distribution by increasing FSP passes. Furthermore, the investigation of strengthening mechanisms showed that grain size decrease, due to recrystallization and pinning effect of particles, had more influence on increasing composite hardness than dispersion hardening. The wear resistance of the composite which underwent 4 passes was 33% more than as-received AZ31B. It also had the highest corrosion resistance due to more stability of the passive film as a result of fine grain size.