System development, formability quality and microstructure evolution of selective laser-melted magnesium

A selective laser melting (SLM) system, which consisted of a fibre laser, a three-dimensional motion platform and a motion control system, was developed in this study. The effect of process parameters on the microstructure evolution of SLMed magnesium parts was investigated. The results revealed that under an irradiation of laser energy density <3.0 J/mm, the powder remained in the discrete state. At a laser energy density 3.0–6.0 J/mm, the powder partially melted and sintered together, yielding incompact tracks. As the energy density increased to 6.0–12.0 J/mm, the powder fully melted forming continuous and smooth tracks. With a further increase in the laser energy density evaporation of the powder occurred. Dense magnesium parts free of pores and cracks were successfully fabricated with the optimal energy density of 10.0 J/mm. The immersion experiment revealed that the degradation product was mainly consisted of Mg(OH)₂, which slowed down the degradation rate acting as a protective layer.