Effects of hot deformation on the heterogeneous interfacial microstructure and shear properties of hybrid manufacturing Mg-Gd-Y-Zn-Zr alloy

The repair and functional enhancement of large magnesium alloy forgings remain challenging. Although wire and arc additive manufacturing (WAAM) allows accurate structural deposition, weak bonding at heterogeneous interfaces restricts its application. To overcome this limitation, hot compression was applied to an as-deposited Mg-Gd-Y-Zn-Zr alloy, integrating WAAM deposition and a forged substrate, at 350-450 °C with true strains of 0.3-0.5. Systematic investigations were carried out to clarify how process parameters govern interfacial microstructure and mechanical properties. Microstructural observations reveal a typical interfacial gradient structure, consisting of equiaxed grains in the additive zone and a substrate-side heat-affected gradient zone (HAGZ) that includes the fusion interface, a remelted eutectic zone, and a eutectic aggregation zone. Notably, HAGZ width expands under ε = 0.3 due to thermally driven diffusion but contracts under ε = 0.5, where plastic deformation dominates. Moreover, the dynamic recrystallization (DRX) fraction increases with temperature, while grain size decreases with strain. Mechanical results demonstrate the close relationship between interfacial behavior and micro-mechanisms. At 350 °C, inadequate DRX leads to high dislocation density, work hardening, and brittle interfacial fracture under shear. At 450 °C and 0.5 strain, β-phase dissolution and recrystallization–recovery improve plasticity (shear strain 19.1%) but lower strength (190.8 MPa). In contrast, the 400 °C-0.5 strain condition achieves an optimal strength-ductility synergy (shear strength 208.0 MPa, shear strain 18.0%) due to the combined strengthening effects of high dislocation density, grain refinement, and dispersed β-phase precipitates. This work demonstrates that hot compression processing significantly improves the interfacial properties of WAAM/forged hybrid components.