Achieving strength-plasticity breakthrough of rare-earth free Mg alloy with multi-scale framework fabricated via laser-cold metal transfer hybrid additive manufacturing

To overcome the drawbacks of low strength and poor plasticity of Mg alloys, this work innovatively employed laser-cold metal transfer (CMT) hybrid additive manufacturing technology to fabricate rare-earth free Mg alloy with outstanding mechanical properties. The laser multi-remelting effect significantly promoted grain refinement and intensified columnar-to-equiaxed transition. The average grain sizes of CMT-zone, laser-induced single remelting zone and laser-induced multi-remelting zone were 15.89 μm, 8.75 μm and 3.56 μm, respectively. The average size of substructure in the laser multi-remelting zone was 310 nm. Due to the synergistic effect of the laser and CMT heat source, a multi-scale framework composed of micro-nano grains and dispersed precipitates was formed. The framework notably enhanced crack resistance, facilitated grain boundary strengthening and activated non-basal slip systems, thereby achieving an exceptional breakthrough of strength and plasticity. The laser-CMT hybrid additive manufacturing Mg alloy exhibited a tensile yield strength (TYS) of 224.8 MPa, an ultimate tensile strength (UTS) of 322.6 MPa and a plastic elongation (PE) of 13.5 %, which reached the levels of deformed Mg alloys. This study introduced a novel and highly promising additive manufacturing approach for producing large-scale and high-performance components made of Mg alloys.