Research on formability, microstructure and mechanical properties of selective laser melted Mg-Y-Sm-Zn-Zr magnesium alloy

Selective laser melting (SLM) refers to a laser additive manufacturing technology. It shows its advantages of high efficiency and is capable of processing arbitrary complex structural parts. However, the SLM of magnesium alloy is highly challenging and should be studied in depth due to the low melting and boiling point of magnesium alloy. In this study, selective laser melting (SLM) technology was used to manufacture the Mg-Y-Sm-Zn-Zr alloy. Microstructure characteristics and performance mechanism of the SLMed samples were investigated. As revealed by the results, samples characterized by relatively high densities and low surface roughness could be produced when the energy density was 83.3-166.7 J/mm3. The highest density of 97.8% could be obtained when the energy density was 125.7 J/mm3. The molten pool was found to consist of slender columnar grains at the edge and a small amount of equiaxed grains at the top, while the grains below the molten pool were coarsened under the action of the thermal influence. The role played by Y2O3 in the solidification of SLM was characterized using the degree of lattice mismatch. Impacted by the high lattice mismatch between Y2O3 and Mg, Y2O3 could not serve as an effective heterogeneous nucleation particle. The highest comperssive performance was obtained at energy density of 125.7 J/mm3 (YS = 304 +/- 5 Mpa, UTS = 394 +/- 5 Mpa). The main strengthening mechanism was fine-grain strengthening, followed by precipitation strengthening and the effect of solid solution strengthening was not obvious. This work provides a certain guiding significance for the follow-up research of SLMed rare earth magnesium alloy.

Automated summary

Selective laser melting (SLM) is a laser additive manufacturing technology that offers high efficiency and is capable of processing complex structural parts. This study investigated the microstructure characteristics and performance mechanism of Mg-Y-Sm-Zn-Zr alloy manufactured using SLM. The results showed that samples with high densities and low surface roughness could be produced at an energy density of 83.3-166.7 J/mm3, with the highest density of 97.8% achieved at 125.7 J/mm3. The molten pool exhibited slender columnar grains at the edge, a small amount of equiaxed grains at the top, and coarsened grains below. The role of Y2O3 in solidification was affected by lattice mismatch and did not serve as an effective nucleation particle. The highest compressive performance was obtained at 125.7 J/mm3, with a yield strength (YS) of 304 +/- 5 Mpa and ultimate tensile strength (UTS) of 394 +/- 5 Mpa. The main strengthening mechanisms were fine-grain strengthening, precipitation strengthening, and the limited effect of solid solution strengthening. This work provides guidance for further research on SLMed rare earth magnesium alloy.