Abstract: Insufficient strength has long constrained the wire arc additive manufacturing (WAAM) of low-cost Mg alloys, largely due to limited compositional control from the difficulties in fabricating high-alloy Mg wires. To overcome this limitation, a laser‐assisted dual‐wire WAAM (laser-DWAAM) strategy that enables in-situ alloying of heterogeneous Mg- and Al-based wires was developed, successfully fabricating Mg-9Al-0.4 Zn (AZ90) alloy with a yield strength (YS) increment of ∼80 MPa after aging. The optimized alloy exhibited remarkable YS ≥ 185 MPa, ultimate tensile strength ≥ 335 MPa, and elongation > 7 %, representing the highest reported strength among WAAM-processed AZ-series alloys. Crucially, the strengthening primarily originated from high-density multi-scale β-Mg₁₇Al₁₂ precipitates, predominantly those with non-basal orientations (long-axis angles ∼35° and 90° to basal plane), which strongly pin basal dislocation slip. Additionally, the laser-arc synergy reduces the surface tension and critical detachment radius of Al droplets, enabling synchronized droplet transfer and thus effectively suppressing defects and elemental inhomogeneity formation. Furthermore, laser-guided enhancement of melt pool dynamics promotes compositional homogeneity and facilitates pore escape, while post-heat treatment eliminates segregation. This study broke through the critical challenges in fabricating high-alloy Mg-Al series alloys via WAAM, establishing a novel paradigm for the controllable manufacturing of high-performance WAAM-processed Mg alloys.

Key words: Wire arc additive manufacturing, Magnesium, Dual-wire in-situ alloying, Heat treatment, Mechanical property