Additive friction stir deposition (AFSD), as a solid-state-additive manufacturing technique with a high deposition rate, provides an innovative route for fabricating high-performance magnesium (Mg) alloys while avoiding solidification defects. In this study, the effects of T6 heat treatment on the microstructure, mechanical properties, and deformation mechanisms of an AFSD Mg-9Gd-3Y-0.5Zr (wt.%) alloy were systematically investigated. The AFSD alloy exhibited a heterogeneous onion-ring microstructure composed of alternating fine grains (~3.9 µm) enriched with nanoscale cuboid Mg₂₄(Gd, Y)₅ precipitates and coarse grains (~10.6 µm) containing limited precipitates, which originated from the non-uniform precipitate distribution in the feedstock. The T6 heat treatment eliminated dislocation structures, introduced abundant nano-Mg₇(Gd, Y) (β′) precipitates and coarsened the fine and coarse grains to ~7.3 and ~67.4 µm, respectively. Consequently, the AFSD and AFSD-T6 alloys achieved superior strength-ductility combinations compared to the feedstock, with yield strength/ultimate tensile strength/elongation of 293.5 MPa/330.3 MPa/8.1% and 366.8 MPa/374.3 MPa/5.1%, respectively. The heterogeneous grains induced pronounced hetero-deformation-induced hardening in both conditions, while basal 〈a〉 slip activity was progressively enhanced during deformation. However, extensive twinning, particularly double twinning in the coarse grains of the AFSD-T6 alloy, led to reduced ductility. Overall, this work demonstrates that coupling AFSD with tailored heat treatment enables effective microstructural heterogeneity engineering, offering a robust strategy for developing Mg-Gd-Y-Zr alloys with outstanding mechanical performance.

Additive friction stir deposition (AFSD), as an advanced solid-state additive manufacturing technique, offers significant potential for fabricating large-scale engineering structural components. In this study, Mg-xAl-1Zn-0.5Mn (x = 3, 6, and 9 wt. %) alloys were fabricated via AFSD. And the effect of Al content on the microstructural evolution, mechanical properties, and fracture behavior was systematically investigated. The results reveal that all AFSD AZ series Mg alloys exhibit refined equiaxed grains and a typical basal texture, with the (0002) axis parallel to the build direction (BD). However, increasing Al content results in a gradual decrease in both average grain size and basal texture intensity. Alloy with low content of Al (≤ 6 wt. %) exhibits uniform grain size and precipitate distribution, whereas alloy with high content of Al (e.g., 9 wt. %) displays a bimodal structure composed of fine grain bands decorated by β-Mg₁₇Al₁₂ phase near grain boundaries and coarse grain bands. For this, a clear strength-ductility trade-off is observed: with increasing Al content, the yield strength rises from 152.8 ± 17.9 MPa to 215.5 ± 17.7 MPa, accompanied by a reduction in fracture elongation from 15.9 ± 0.6% to 12.3 ± 0.6%. These findings can offer theoretical insight and practical guidance for the AFSD AZ series (Mg-Al-Zn-Mn) alloys with synergistic strength and ductility.

Twinning-detwinning (TDT) behavior in a strongly basal-textured Mg-Li alloy during two-step compression (RD)-compression (ND) process was investigated using quasi-in-situ EBSD. TDT behavior and TDT variants selection were statistically discussed with the loading path for the first time. Non-Schmid twinning behavior was observed in the first step compression, owing to the local stress fluctuations by neighboring twins; in contrast, Schmid’s law well predicted the detwinning variants selection. This asymmetrical TDT behavior was first investigated to date related with the strong basal texture and loading path. Besides, with the progress of compression, Schmid factors for twinning demonstrated a decreasing tendency; however, those for detwinning during the second step displayed an abnormally increasing trend, fundamentally stemming from prior twinning behavior.