| With the continuous improvement of product performance requirements in various engineering fields,complex and integrated design has become the development direction of future product design.Traditional manufacturing processes,such as casting,forging,powder metallurgy,etc.,are increasingly limited in the production of complex structural components,and costs are rising significantly.Laser Powder Bed Fusion（LPBF）is a new manufacturing technology,which can produce high-precision and dense complex metal parts without post-processing,greatly shortening the production cycle.Al-Mg alloy is widely used in aerospace and marine equipment manufacturing because of its good corrosion resistance,weldability and mechanical properties.When Al-Mg alloy with a small amount of alloyed elements Sc and Zr is formed by LPBF technology,the grain can be refined significantly,and the high density nanoscale Al3（Sc,Zr）precipitated phase can be formed,further improving its comprehensive properties.Based on this,Al-Mg-Sc-Zr alloy was fabricated by Laser Powder Bed Fusion（LPBF）technology,and the effects of remelting scanning and heat treatment on the microstructure evolution,mechanical properties and corrosion resistance of Al-Mg-Sc-Zr alloy were investigated.The main conclusions are as follows:The surface roughness（Sa）of the non-remelt scan is similar to that of the first remelt scan,while the surface roughness（Sa）of the second remelt scan is significantly improved.With the increase of scanning times,the side surface roughness（Sa）of the sample increases gradually.The hardness of the side of the sample is higher than that of the upper surface in different remelting scanning processes.The highest density and the highest surface hardness of the remelting scanning process is 99.3%,with the upper surface scanned twice and the side profile scanned once.The corrosion resistance of Al3（Sc,Zr）phase decreases with the increase of remelting scanning times.The molten pool boundary on the upper surface and side of the printed sample is composed of fine equiaxed crystals,while the inner molten pool has a different structure.The inner molten pool on the upper surface is a coarser cellular crystalline structure,while the side is a coarser columnar crystalline structure.The orientation of the crystals in the inner and boundary of the upper molten pool is random,while the columnar crystals in the inner side molten pool are<001>oriented texture.Most of the grain boundaries in the inner and boundary regions of the molten pool on the upper surface and side are high Angle grain boundaries,and the defect density in the fine equiaxed crystal region at the molten pool boundary is much higher than that in the coarse crystal region inside the molten pool.The edge of a molten pool is more prone to corrosion than the inside of a molten pool.After aging treatment,a large number of Al3（Sc,Zr）particles will be precipitated in the molten pool.After aging at 325℃/4h,the mixed crystal structure and grain orientation of the alloy side have no obvious change.After aging at 475℃/4h,the fine isaxed crystals at the boundary of the molten pool will be coarsened,while the coarse columnar crystals inside the molten pool will be recrystallized,and their<001>direction texture will gradually weaken.The grain boundary characteristics and defect density distribution of Al-Mg-Sc-Zr alloys are not changed by aging treatment.After aging treatment,the corrosion resistance,hardness,yield strength and tensile strength of the samples were significantly increased,while the elongation at break was decreased.Compared with the upper surface of the sample in the same state,the corrosion resistance of the side is lower.The printed specimens are ductile fracture.With the extension of aging time at 325℃,the fracture mode changes from ductile fracture to shear fracture.After being etched by 3.5wt%Na Cl solution,the mechanical properties of the heat-treated specimens are still higher than those of the printed specimens,but the plasticity is reduced more obviously. |
