Microstructure and properties of high-strength Al-Mg-Sc alloys fabricated by selective laser melting

By comprehensive analysis of macroscopic characteristics of hardness, electrical conductivity and tensile properties and features of microcosmic morphology, the influence mechanism of process parameters of laser selective melting and following aging treatment on the microstructure, supersaturated solid solution and second-phase precipitation behavior of Al-3.4Mg-1.08Sc alloy fabricated by SLM was discussed. By utilizing the change rules of density and hardness,finally the optimum SLM process parameters and aging system were obtained.The results show that the microstructure of the Al-Mg-Sc alloy fabricated in this experiment is composed of ultrafine equiaxed grains and relatively coarser columnar grains around. The optimal fabrication parameter of Al-Mg-Sc alloy fabricated at platform temperature of 35 ℃ is conducted with scanning speed of 1600 mm/s, laser power of 370 W. The optimum aging time is 12 h at 300 ℃, the yield strength of studied alloy can reach 479.0 MPa through peak aging treatment. Under rapid cooling rate of SLM process, supersaturated solid solution is formed in Al-Mg-Sc alloy, and a large number of nanometer Al3(Sc,Zr) particles are precipitated during the fabrication and heat treatment process, which makes the Al-Mg-Sc alloy present excellent potential of mechanical properties. The fine grain strengthening and the second phase strengthening are the main factors for exhibiting properties of Al-Mg-Sc alloy fabricated by SLM.