Enhancing wear resistance of wire-arc directed energy deposition Mg alloy via introducing high-density twins and dislocations

It is a huge challenge for the wear resistance of Mg alloys in applications such as transmission friction components. This is also critical for Mg components prepared by wire-arc directed energy deposition (WA-DED). In this study, a superior wear resistance in WA-DED manufactured AZ31 Mg thin-walled component with high-density twins and dislocations was achieved by employing the deformation field originating from ultrasonic impact treatment on each deposited layer. The introduction of high-density twins and dislocations refined the microstructure under their splitting grain effect. Meanwhile, the hardness of components was enhanced, resulting in lower coefficient of friction and wear rates. And worn tracks exhibited milder wear characteristics such as abrasive and oxidation, delamination-free was detected compared with components without twins and dislocations. The improved wear resistance mainly resulted from twins and dislocations pile-up inducing the hardening effect and the higher work hardening response during sliding, inhibiting surface deformation and crack propagation. Additionally, the uniform tribo-oxide layer formed by introducing numerous twin boundaries also played an important role in suppressing material spalling, thermal softening and melting at higher sliding velocities. This study provides a novel strategy for preparing WA-DED Mg alloy thin-walled components with the excellent wear resistance.