Multi-objective optimization of friction stir processing of AZ31B magnesium alloy
Abstract
ABSTRACT AZ31B magnesium alloy is extensively utilized in lightweight structural and transportation applications due to its superior strength-to-weight ratio; however, its structural performance is often limited by coarse-grain structure, microstructural heterogeneity, and reduced mechanical integrity. To overcome these limitations, the present study investigates the effect of friction stir processing (FSP) on AZ31B magnesium alloy to enhance its mechanical, microstructural, corrosion, and thermal properties. The influence of key FSP parameters, including tool rotational speed (800–1200 rpm), traverse speed (60–100 mm/min), and tool pin profile (cylindrical, pentagonal, and hexagonal), was systematically evaluated using a face-centered central composite design integrated with response surface methodology and analysis of variance. The experimental results demonstrated significant improvement in tensile strength, microhardness, wear resistance, and impact toughness due to grain refinement, uniform plastic deformation, and dynamic recrystallization during friction stir processing. The maximum tensile strength (178.8 MPa) and microhardness (78.4 HV) were achieved at 1200 rpm rotational speed, 60 mm/min traverse speed, and hexagonal pin profile. Microstructural analysis confirmed the formation of fine, equiaxed grains resulting from dynamic recrystallization within the stir zone. Corrosion analysis revealed improved electrochemical stability due to refined grain structure and uniform phase distribution. Thermal analysis further indicated enhanced thermal stability of the processed zone. Statistical optimization confirmed the strong influence of process parameters on mechanical performance and validated the predictive capability of the developed models. The findings demonstrate that friction stir processing is an effective approach for improving the multifunctional performance and structural reliability of AZ31B magnesium alloy for advanced lightweight engineering applications.