Comparison of microstructure, wear resistance, and corrosion behavior of AZ31B/SiO2, AZ31B/graphite, and AZ31B/SiO2/graphite surface composite produced by friction stir processing (FSP)

In this research, silica nanoparticles, graphite nanoparticles, and a mixture of silica and graphite nanoparticles were used to fabricate surface composites on AZ31B by the use of friction stir processing (FSP). The results after 4 passes indicated that, in comparison with as-received AZ31B, the mean grain size in the sir zone for AZ31B/SiO2, AZ31B/graphite, and AZ31B/SiO2/graphite decreased about 82%, 70%, and 80% respectively. Furthermore, in comparison with as-received AZ31B, microhardness increased 33%, 18.8%, and 20.6% respectively. Although graphite, as a solid lubricant, decreased hardness, the results of wear test indicated that wear rate of AZ31B/graphite and AZ31B/SiO2/graphite is almost similar to wear rate of AZ31B/SiO2. The investigation of TEM images indicated that the size of sub-grains for AZ31B/SiO2/graphite was 18% smaller than AZ31B/SiO2. Furthermore, the results of the corrosion test indicated that the corrosion current of AZ31B/SiO2 reduced over 89% compared with as-received AZ31B, and AZ31B/SiO2/graphite had the highest corrosion potential.