Selective laser melting of a novel Sc and Zr modified Al-6.2 Mg alloy: Processing, microstructure, and properties

Abstract

The interest of additive manufacturing (AM) Al-base alloys for lightweight applications, especially the novel scandium modified Al-Mg alloy is growing. In this work, the selective laser melting (SLM) of Al-6.2Mg-0.36Sc-0.09Zr alloy was systematically investigated, with a particular emphasis on densification, microstructure and properties. An increased laser energy density leads to a higher densification level and a better the surface finish of the SLM samples. The surface exhibits a large number of oxides at the scan track interface and microcracks owing to the high Mg content. The x-ray diffraction reveals a (200) texture due to the preferential solidification in the 〈100〉 direction and the diffraction peaks shift to a higher angle after the laser melting owing to the Mg loss. The horizontal plane presents equiaxed grains while the vertical plane presents columnar ones with the aggregation of 〈001〉 orientation. The microstructure exhibits alternately coarse and fine grain that beneath the weld pool is a fine grained band while the central zone of weld pool shows coarse columnar grains epitaxial above the fine grain band, which is caused by the segregation of Al3(Sc,Zr) particles in weld pool boundary. The microhardness of the densest part is directionally independent, which is much higher than cast alloy but lower than homogenizing annealed alloy. The maximal compression strength of SLM Al-Mg-Sc-Zr alloy reaches 390.25MPa. The electrochemical corrosion property of SLM alloy is higher than cast one. Better understanding of the metallurgical mechanisms during SLM of the present alloy will help pave the way for designing SLM suitable Al-base alloys.