Engineering Corrosion-Resistant Microstructures in AZ31D Magnesium Alloy through Friction Stir Processing

In this study friction stir processing (FSP) was utilized to refine the microstructure of thick AZ31D magnesium (Mg) alloy, followed by evaluation of its microstructure and corrosion behavior in a NaCl environment. The application of a tapered threaded pin profile resulted in enhanced material mixing, significant grain refinement and reduced defect formation due to minimal heat input and minimized thermal gradients across the stir zone (SZ). The SZ, dominated by the pin profile, exhibited a fine, equiaxed, and uniform grain structure throughout its thickness the average grain size reduced from 13.8 µm to 5.19 µm after second pass of FSP confirmed through field-emission scanning election microscopy (FE-SEM) analysis. This structural refinement significantly enhanced the corrosion performance of the FSPed alloys, as compared to the base material (BM), demonstrated by electrochemical testing in 3.5% NaCl solution. The FSPed alloy surface showed uniform corrosion behavior, instead of intergranular corrosion with deep mud cracking patterns observed in the BM. This improved corrosion resistance was due to the uniformity of the produced microstructure via FSP, which reduced localised corrosion sites. These findings suggest that FSP is a promising technique for improving the durability of Mg alloys in corrosive environments, potentially benefiting applications in the automotive and aerospace industries.