Effect of laser power on microstructures and properties of Al-4.82Mg-0.75Sc-0.49Mn-0.28Zr alloy fabricated by selective laser melting

In this paper,a high strength Al-4.82Mg-0.75Sc-0.49Mn-0.28Zr (Al–Mg-Sc-Mn) alloy was prepared by selective laser melting (SLM). The effects of laser power on microstructures, relative density, and mechanical properties of SLM-fabricated Al–Mg-Sc-Mn alloy were studied. The results shown that the bimodal structure with an ultra-equiaxed grain and columnar crystal is formed in Slammed-fabricated Al–Mg-Sc-Mn alloy. The columnar crystal is surrounded by ultra-fine equiaxed crystal, and the columnar crystal shows (001) preferred orientation, the ultra-fine equiaxed structure shows no anisotropy in SLM-fabricated alloy. With increase of laser power, the molten pool size increases during SLM process, and the samples relative density and hardness decrease as laser power increase. The relative density of SLM-fabricated Al–Mg-Sc-Mn alloy is 99.74% under the process parameters of laser power 310W and scanning speed 1200 mm/s, and the hardness of alloy is as high as 107.73 ± 1.27 HV. The tensile strength of SLM-fabricated Al–Mg-Sc-Mn alloy samples are all higher than 400 MPa, and elongations are more than 19%. The fracture morphology of SLM-fabricated Al–Mg-Sc-Mn alloy is a typical ductile fracture feature, which shows a high comprehensive mechanical property. Supersaturated solid solution is formed in Al–Mg-Sc-Mn alloy because of rapid cooling during SLM process, resulting in grain refinement and improvement of mechanical properties. Fine-grain strengthening and second phase strengthening are the main reasons for the improvement of mechanical properties of SLM-fabricated Al–Mg-Sc-Mn alloy.