Understanding the processing, microstructure, and deformation behavior of AZ31B Mg alloy fabricated by additive friction stir deposition

Solid-state additive manufacturing offers significant advantages in the fabrication of magnesium (Mg) alloys. These benefits include the avoidance of metal melting, the elimination of the requirement for a protective atmosphere, and enhanced operational safety. In this study, a multilayer AZ31B Mg alloy deposit was successfully fabricated using a solid-state additive manufacturing technique known as additive friction stir deposition (AFSD). The processing parameters for the deposition of AZ31B Mg alloy were initially investigated, leading to the successful fabrication of a 36-layer AZ31B Mg alloy deposit under optimized parameters. Subsequently, the microstructural characteristics and mechanical properties of the multilayered AZ31B Mg alloy were systematically analyzed. Finally, the underlying deformation mechanisms were comprehensively examined through detailed quasi-in-situ electron backscatter diffraction (EBSD) analysis. The results show that the grains of the final deposits are significantly refined and have a good uniformity, with the average grain size reaching similar to 20 mu m, due to the dynamic recrystallization under repeated thermal-mechanical deformation. The deposited grains exhibit a strong basal texture with the c-axis of the grains parallel to the build direction (BD). The microhardness exhibits uniformity from the bottom to the top of the deposited layer due to the uniform grain size distributions and precipitates. Owing to the strong basal texture and the pole nature of extension twinning, the yield strength in different directions shows a pronounced anisotropy, whilst the ultimate tensile strength and elongation in different directions are relatively comparable except for one path with a high basal slip apparent Schmid factor. In addition, compared to Mg alloys manufactured by melting additive manufacturing techniques, the AZ31B Mg alloy prepared by solid-state AFSD in this study shows a higher mechanical strength.