Abstract:In-situ alloying employs compositional design to mix commercially available powders in specific ratios as feedstock for fabricating alloy components by selective laser melting (SLM), potentially addressing challenges in preparation of pre-alloyed powder. Melt-track and bulk samples of multi-component rare-earth Mg-3.4Y-3.6Sm-2.6Zn-0.8Zr magnesium alloy were fabricated by SLM in-situ alloying method using Mg, Y, Sm, Zn, and Zr commercial powders as raw materials. The formability, relative density, surface morphology, microstructure and microhardness of the samples under different process parameters were investigated and compared with those of the pre-alloyed powder formed samples. The results show that single melt-track can obtain a stable and smooth melt-track at a laser power of 80 W, and the melt pool is in conduction mode. The bulk sample has the maximum relative density of 98.71% at a laser power of 80 W, and a scanning speed of 300 mm/s, with the fewest pores and unmelted particles and a microhardness of 98.97 HV. The phase composition of the in-situ alloyed samples is composed of Mg matrix, Y-Zr-O rare-earth oxides, and eutectic phase (Mg,Zn)3(Y,Sm), and the microstructures are mostly fine equiaxed grains.