Microstructural, mechanical, and corrosion behavior of ZrO₂, HA, and Y₂O₃ hybrid reinforced AZ91D alloy surface composites fabricated through FSP route

In the present work, ZrO₂, HA, and Y₂O₃ hybrid reinforced AZ91D alloy surface composites were fabricated using multi-passes friction stir processing (FSP) route. Consequently, microstructure, microhardness, tensile, and corrosion behavior were thoroughly examined on processing passes. The FSP passes increased coarse-shaped grains which were gradually refined into finer equiaxial grains due to severe plastic deformation and equal dispersion of reinforcements. Microhardness values successfully increased with the incorporation of hybrid reinforcements and increasing FSP passes. Tensile tests demonstrated decreased ultimate tensile strength as compared to substrate materials but an increase compared to 1 pass to 3 passes. Due to grain arrangements, grain dislocations decreased between surface matrices. Corrosion rate increases with the number of days; however, when FSP passes rise, compared to FSP passes, corrosion rate also increases due to the formation of secondary surface layers on the surface.