Formability, microstructure, and thermal crack characteristics of selective laser melting of ZK60 magnesium alloy

Abstract

ZK60 magnesium alloy was processed by selective laser melting (SLM), and the influences of different process parameters on the quality of the samples were investigated. The microstructures, mechanical properties, and crack characteristics of SLMed ZK60 Mg alloy were analyzed. The results showed that high quality of the SLMed ZK60 Mg alloy was obtained at a laser energy density of 291.6 J/mm3; the relative density of the samples was >99%, and the surface roughness was 17.6 μm. The microstructure comprised an equiaxed zone, a lamellar zone, and a heat-affected zone (HAZ). Sizes of the equiaxed grain and HAZ were 8 μm and 10 μm, respectively. At the boundary of the molten pool, alloy element Zn was segregated, which formed a low melting point eutectic phase, leading to development of thermal cracks. At the optimal laser energy density, the thermal cracks were mainly liquation cracks. Despite the presence of a few liquation cracks in the samples, the fine grains and the nano precipitated phase played a key role in the mechanical properties of the sample. The tensile strength and elongation of the SLMed ZK60 Mg alloy were 246.3 MPa and 15.5%, respectively. Thus, SLM holds great promise for the manufacturing of high-density ZK60 components with a tensile strength comparable to conventional castings.