Friction stir processing of AZ31/ yttria stabilized zirconia (YSZ) surface composites: tribological benefits of an optimized tool pin profile

This research investigates the impact of various tool pin profiles on the tribological behavior of AZ31 magnesium alloy reinforced with 5 wt.% yttria-stabilized zirconia (YSZ) surface composite produced through friction stir processing (FSP). AZ31 plate filled with YSZ subjected to FSP using four distinguished tool profiles: plain cylindrical (PC), threaded cylindrical (TC), plain tapered cylindrical (PTC) and threaded tapered cylindrical (TTC). Dynamic recrystallization due to the FSP process contributed to fine grain structure refinement and uniform distribution of YSZ particles, resulting in improved hardness of AZ31/YSZ surface composites. The wear behavior was examined by means of a pin-on-disc tribometer under 15, 30, and 45 N applied loads. Results reveal that the FSPed AZ31/YSZ composites had higher wear resistance compared with those for as-received, and FSPed AZ31 alloy. Plain tapered cylindrical tool profile gave better outcomes which included defect free surface finish and optimal particle dispersion. It was shown that stronger YSZ particles inhibit material removal and increased refined grain structure, supported by a decrease in coefficient of friction from 0.49 for as received AZ31 alloy to 0.27 for FSPed AZ31/YSZ composites emphasizes the influence of FSP tool pin profiles in enhancing the hardness and tribological performance of surface composites.