Microstructure evolution and age-strengthening mechanism of Mg-Gd-Y-Zr alloy fabricated by additive friction stir deposition

Solid-state deposition additive manufacturing technology demonstrates significant advantages in fabricating high-strength rare-earth magnesium (Mg-Re) alloy components, including low forming temperature, high densification, uniform composition, and high efficiency. Here, a high-strength single-pass multilayer Mg-8Gd-3Y-0.5Zr alloy component was fabricated by the additive friction stir deposition (AFSD) method with an average layer thickness of 4 mm. The results indicate that the microstructures of the top, middle, and bottom regions of the AFSD component were equiaxed grain, with an average grain size of approximately 7.42 ± 0.58 µm. The interface region underwent two stages of plastic deformation under the separate effects of the shoulder and the feedstock, finer equiaxed grains were formed, with an average grain size of about 2.79 ± 0.14 µm. After artificial aging at 225 °C for 20 h, a large number of nano-β′ precipitates are uniformly distributed within the material. The ultimate tensile strength reached 355.52 ± 3.21 MPa in the building direction and 433.91 ± 2.31 MPa in the longitudinal direction, there is an increasing of 49.0 % and 45.9 % compared to the AFSD samples. No grain growth was observed in the interlayer and the interface after aging treatment. The finely dispersed nano-β' precipitates produced by artificial aging treatment are the key factor to improve the tensile strength of the deposited layer. The primary strengthening mechanisms were identified as precipitation strengthening and grain refinement, contributing 54.8 % and 26.7 % to the overall strengthening effect, respectively. These findings suggest that AFSD offers a novel and efficient solution for the fabrication of large-scale Mg-Re alloy components.