Processability And Properties Of Al-Mg-Mn-Er-Zr Alloy For Selective Laser Melting

Selective laser melting（SLM）is a kind of additive manufacturing technology,which can realize the direct prototyping of complex metal parts.Aluminum alloy is an important lightweight material,which is widely used in aerospace,transportation and other fields.Nowadays,SLM forming high-performance aluminum alloy is mainly limited to Al-Mg-Mn-Sc-Zr.However,the content of the Sc element in this alloy contains is high,which increases the cost of the raw material.Based on this condition,the cheaper Er element is used to replace the Sc element in the Al-Mg-Mn-Sc-Zr alloy.The effects of process parameters on the formability of Al-2.74Mg-6.01Mn-0.86Er-0.52Zr alloy are systematically investigated in this study.In addioion,the aging treatments on the microstructure and mechanical properties of Al-Mg-Mn-Sc-Zr alloy are also studied in this article.The results are as follows:（1）Al-Mg-Mn-Er-Zr powder samples have been fabricated by the gas atomization method.The morphology and particle size distribution of the powder were characterized,and the forming quality of the powder samples under different laser power was studied.The results show that the sphericity of powder samples is excellent,and the distribution of particle size is uniform.When the powder samples are subjected to the low laser power（250W）,there are many irregular unfused holes in the samples due to the low laser energy input.Under the effects of internal stress,there are many microcracks in the samples,which reduces the forming quality of the samples.When the laser power increases to 350 W,the structure of the samples is dense and crack-free at low laser scanning rates.The relative density of the samples is the highest（98.89%）,and the formability of samples is superior.（2）Studies on microstructure and properties of as-builted samples.The SLM-formed samples are mainly composed of fine equiaxed crystals at the boundary of the molten pool and coarse columnar crystals in the molten pool.Due to the dependent precipitation of Al₃Er and Al₆Mn precipitates during the solidification of melt,the grain refinement of Al₃Er particles is weakened,and the number of equiaxed crystals in the samples decreases compared with the SLM formed aluminum alloy modified by Sc.The Vickers hardness of the as-builted samples is 154±2 HV,the yield strength（YS）of the samples is 327±3 MPa,the ultimate tensile strength（UTS）is 502±2 MPa,and the fracture elongation is about12.2±1%.Its strength is higher than that of Al-4.6Mg-0.49Mn-0.66Sc-0.42Zr alloy formed by SLM（YS=280±6.1 MPa）.（3）Effect of aging processes on mechanical properties.Under the aging time of 2 h at different temperatures,Vickers hardness first increases and then decreases with the increase of temperature.The maximum hardness of the samples is about 154±2 HV at the aging temperature of 350℃.After isothermal aging at 350℃,the hardness of SLM samples first increases and then decreases with the increase of aging time.The maximum hardness of the samples is 171±1 HV at the aging time of 6 h.the compressive yield strength of SLM samples first increases and then decreases with the increase of aging time.the compressive yield strength of the samples is the maximum（555±12 MPa）at the aging time of 6 h.The YS and UTS of the samples are 339±2 MPa and 508±1 MPa respectively.The strength of these samples is similar to that of traditional SLM-formed Al-Mg-Sc-Zr alloy.Due to the second phase strengthening caused by the precipitation of Al₆Mn phases,the strength of samples with aging treatments has been effectively improved.