Selective laser melting of Mg-Zn binary alloys: Effects of Zn content on densification behavior, microstructure, and mechanical property

Mg-Zn binary alloys with seven distinctive compositions (Zn (wt.%) = 1, 2, 4, 6, 8, 10 and 12) were prepared using a selective laser melting (SLM) additive manufacturing technology. Densification behaviors and microstructure of the SLM-processed alloys were analyzed using quantitative metallography analysis, XRD, SEM, and EDS. The mechanical property characterizations were carried out through microhardness and uniaxial tensile tests. The results showed that the increase of Zn content had a significantly deteriorating effect on the densification response of the SLM-processed Mg-Zn alloys. At 1 wt% Zn content, near full-dense products could be obtained. At 2-10 wt% Zn contents, SLM-processed alloys suffered from solidification cracking and the crack density showed an approximate A-shaped variation trend with the increase of Zn content. At 12 wt% Zn content, solidification cracks were eliminated but lots of micro-pores formed within the SLM sample. All the SLM samples exhibited a duplex microstructure composed of alpha-Mg matrix and Mg7Zn3 eutectic phase. With the increase of Zn content, the quantity of Mg7Zn3 increased continuously whilst its morphology gradually transformed from granular shape to nearly reticular structure. The hardness and tensile tests showed that only the Mg-1Zn sample has comparable mechanical properties with the as-cast counterpart. At higher Zn contents, mechanical properties of the SLM-processed alloys became significantly degraded, mainly because of the deterioration of the densification degree.