Friction stir processing of hybridized AZ31B magnesium alloy-based composites by adding CeO₂ and ZrO₂powders: mechanical, wear, and corrosion behaviors

To improve the properties of AZ31B Mg alloy and for the first time, the rare earth cerium oxide (CeO₂) and zirconium dioxide (ZrO₂) were combined for synergistic benefits and introduced into the structural AZ31B magnesium alloy through the solid-state friction stir processing procedure to form the hybridized AZ31B Mg/ZrO₂+CeO₂ composites under variable levels of the tool's rotational speed up to 1200 rpm. The macro-/microstructure, hardness, shear punching strength, tensile strength, corrosion behaviours, and tribological characteristics such as weight/wear loss, wear rate, coefficient of friction, worn surfaces, and debris of the AZ31B Mg/ZrO₂+CeO₂ hybrid composites were investigated and compared. The results indicated that void, tunnel defect, and ZrO₂+CeO₂ agglomeration could not be prevented at low speed (800 rpm) while defect-free composites were obtained at high speed (1200 rpm). Grain refinement from 7.39 μm to 3.38 μm and the ZrO₂+CeO₂ fragmentation (4.52–2.49 μm) ensued after a rise in the tool's rotational speed owing to higher plastic straining, dynamic recrystallization, and ZrO₂+CeO₂ particle-aided pinning effects. Improvements in hardness (99–135 HV), shear punching strength (121–237 MPa), tensile strength (172–228 MPa) and wear properties of the composite were attained due to the defect elimination, inherent finer Mg grains, and the uniformly dispersed ZrO₂+CeO₂ particles. These attributes also enhanced the corrosion resistance of the AZ31B Mg/ZrO₂+CeO₂ composite at the elevated rotating speed of the tool. The combination of the CeO₂ and ZrO₂ particles is an effective particle-blend for improving the properties of Mg alloy to expand its application scope.