Enhancement of mechanical properties in AZ91D magnesium alloy via wire arc additive manufacturing: influence of rapid solidification and solute segregation on microstructure and deformation behavior

Abstract

The short-process fabrication of high-performance magnesium alloys holds great promise for aerospace and automotive applications, driving advancements in high-end manufacturing. In this study, tungsten inert gas (TIG)-protected wire arc additive manufacturing (WAAM) was employed to produce AZ91D Mg alloy with a weakly textured, equiaxed grain structure. The resulting alloy exhibits an ultimate tensile strength of 284 MPa and uniform elongation of 12.5 %, facilitated by enhanced work hardening. Optimized solidification conditions "freeze" solute atoms in a supersaturated state, inhibiting diffusion and precipitation, and result in a heterogeneous solute distribution. The elevated Al solute concentration suppresses twin propagation, leading to the formation of refined twin lamellae. The ensuing interactions between these fine twins and dislocations play a pivotal role in enhancing the work hardening capability. Additionally, the gradient distribution of Al solute atoms, together with the grain boundary segregation of Al/Zn, effectively weakens the texture, thereby preserving the mechanical isotropy of the WAAM-AZ91D alloy. Additionally, a gradient distribution of solid solution Al atoms extending from grain boundaries to the interior establishes a hardness gradient, effectively alleviating stress concentrations at grain boundaries during deformation and enabling uniform plastic deformation of WAAM-AZ91D. This work expands the application of post-treatment-free short-process fabrication techniques as an effective strategy for the rapid production of high-performance magnesium alloys, broadening their application scope.