Revealing microstructure–property relationships in wire‐arc DED AZ31 alloys: mechanical enhancement and corrosion behavior

Abstract Wire‐arc directed energy deposition (DED) offers promising potential for fabricating large‐scale Mg alloy components, yet the corrosion behavior of additively manufactured AZ31 Mg alloys remains poorly understood. This study systematically investigates the interplay between grain structures (size and orientation) and the mechanical–corrosion performance of wire‐arc DED AZ31 Mg alloys through tailored deposition strategies: straight‐line deposition (AD), arc oscillation (AD‐O), SiC doping (AD‐S), and their hybrid (AD‐OS). Results reveal that grain refinement (from 98.5 (AD) to 19.7 μm (AD‐OS)) significantly enhances mechanical properties—yield strength and elongation are increased by 67.3% and 134.4%, respectively. This can be attributed to grain boundary strengthening and homogeneous strain distribution. However, refined grains exacerbate corrosion susceptibility, with corrosion rates rising from 3.57 mm year −1 (AD‐O) to 5.29 mm year −1 (AD‐OS) in 3.5% NaCl solution. Crucially, grain orientation dominates corrosion resistance: grains with (0001) basal texture exhibit 50% lower corrosion rates than those with prismatic orientations due to higher atomic coordination density. Severe inter‐layer corrosion in AD components stems from fine‐grained regions at fusion lines, while AD‐O components with uniform coarse grains achieve superior corrosion resistance. Quasi‐in situ EBSD/SEM analyses further confirm that micro‐galvanic corrosion at Al‐Mn/α‐Mg interfaces and grain boundary density govern degradation kinetics. This work elucidates the dual effects of grain structures (size and orientation) on mechanical enhancement and corrosion degradation in wire‐arc DED AZ31 Mg alloys.