Preparation And Mechanical Properties Of High Strength Aluminum Alloy By Selective Laser Melting

Designing defect-free and high-strength aluminum alloys suitable for selective laser melting technology is one of the research hotspots in the field of additive manufacturing.In this study,the selective laser melting technology was used to prepare an Al-Mg-Si-Sc-Zr alloy with basic defects.The alloy exhibited a typical melting pool structure consisting of ultrafine equiaxed grains at the edge of the melting pool and coarse columnar grains in the interior.The density of the Al-Mg-Si-Sc-Zr alloy increased rapidly with the increase of laser energy density and then showed a slow decrease.The maximum density of the alloy was 99.86%at an energy density of114.8 J/mm³（corresponding to process parameters of laser power 310 W and scanning speed 900 mm/s）.The tensile properties and orientation effect of the Al-Mg-Si-Sc-Zr alloy were systematically studied in this study.The tensile strength and uniform elongation of the alloy in the horizontal direction（HD）and the build direction（BD）were basically the same,with a difference of less than 3%from the actual tensile strength value,showing quasi-isotropic properties.In addition,as the laser energy density increased,the tensile strength and yield strength of the printed parts showed an initial increase and then a decrease,with a maximum tensile strength of 489.6MPa and a corresponding uniform elongation of 12.2%.This strength is due to the strengthening effect of fine grains,high Mg content solid solution strengthening,refinement of Mg-Si phases into columnar grains,and the inhibitory effect of Si on thermal crack defects.Microstructural analysis showed that the as-prepared Al-Mg-Si-Sc-Zr alloy consisted of sub-micron equiaxed grains and micron-sized columnar grains.The equiaxed grains had a random orientation without texture,while the columnar grains had a weak（100）∥BD fiber texture and were divided into sub-micron-sized sub-grains by strip-shaped Mg₂Si phases.The weak fiber texture and nearly equiaxed sub-grains result in comparable tensile properties in both horizontal and build directions,thus exhibiting quasi-isotropic tensile performance.By mixing Al-Zn-Mg-Cu alloy powder into Al-Mg-Si-Sc-Zr,defect-free Al-Mg-Si-Zn-Sc-Zr-Cu alloy was prepared using selective laser melting technology.The microstructure of the alloy also consists of ultrafine equiaxed grains and coarse columnar grains.Mg and Zn elements mainly exist in the form of solid solution.When the mixing amount of Al-Zn-Mg-Cu alloy powder is 10 wt.%,the surface quality of the formed Al-Mg-Si-Zn-Sc-Zr-Cu alloy is the best,and no obvious cracks or defects were found.With the increase of laser scanning speed,the tensile strength and uniform elongation of the alloy first increase and then decrease.When the laser power is 370 W and the laser scanning speed is 650 mm/s,the formed alloy sample has the maximum tensile strength of 513.1 MPa,and the corresponding uniform elongation is 12.2%.Selective laser melting Al-Mg-Si-Zn-Sc-Zr alloy shows excellent strength-ductility match due to the additional solid solution strengthening effect of Zn and good forming quality.Its performance is 23.5 MPa higher than that of Al-Mg-Sc-Zr alloy,while the elongation rate has not decreased.This provides an experimental basis for the design and preparation of new selective laser melting high-strength aluminum alloys.