Microstructure And Mechanical Properties Of Al-Mg-Sc Aluminum Alloy Fabricated By Selective Laser Melting

Selective Laser Melting（SLM）is a rapid prototyping technology based on laser and powder bed,which can be used to manufacture metal parts with complex structure and excellent performance.Al-Mg-Sc aluminum alloys have good comprehensive mechanical properties and corrosion resistance,and have broad application prospects in aerospace and other fields.At the same time,light and complex metal parts with excellent performance can be obtained by combining selective laser melting technology and Al-Mg-Sc aluminum alloy.In this paper,the selective laser melting Al-Mg-Sc alloy is taken as the research object,and the influence of process parameters such as scanning speed and layer thickness on the microstructure and mechanical properties of the alloy is studied;By comparing the printed and cast alloy samples,the heat treatment effect of process on the microstructure and mechanical properties of Al-Mg-Sc alloy,and explore its heat treatment strengthening mechanism.The main research contents are as follows:（1）The influence of process parameters on the forming quality of Al-4.85Mg-0.74Sc-0.48Zr alloy was studied,and the appropriate SLM process parameters were obtained.It is found that the relative density of Al-4.85Mg-0.74Sc-0.48Zr alloy formed by SLM first increases and then decreases with the increase of scanning speed,and the relative density increases first and then decreases with the increase of laser power.And with the increase of the powder layer,the forming quality decreases significantly.Through research,it is found that the excellent SLM printing process parameters of Al-4.85Mg-0.74Sc-0.48Zr alloy are:laser power 320 W,scanning speed 1250 mm/s,scanning distance 0.13 mm,layer thickness 30μm,under this process parameters,the alloy has optimal SLM formability,the density can reach 99.89%.（2）The study found that the Al-Mg-Sc alloy formed by selective laser melting has a bimodal structure in which ultrafine equiaxed crystals and columnar crystals alternately exist.The equiaxed crystals have random orientation,while the columnar crystals present a<001>preferred orientation.A variety of second phase particles such as Al₃Sc,Al₃Zr and Al₆Mn exist in the Al-Mg-Sc alloy formed by SLM.And the Al₃Sc,Al₃Zr particles and the matrix alloy maintain a highly coherent relationship.The bimodal grain microstructure and grain size of the Al-Mg-Sc alloy after SLM forming did not change significantly after aging treatment at 325℃,indicating that the precipitation of the second phase particles hindered the grain growth.After SLM forming Al-Mg-Sc alloy annealed at 500℃,the bimodal grain structure 8of the alloy gradually faded,the equiaxed grains re-growth,the columnar grains were truncated and grew up,and the precipitation of the second phase particles increased.（3）The friction behavior and mechanical properties of Al-Mg-Sc alloys with different SLM forming process parameters were studied.When the alloy is in the optimal process parameters,it has the best friction and mechanical properties,the relative density reaches 99.87%,and the average yield strength,tensile strength and elongation after fracture are 384 MPa,431 MPa and 17.5%.The SLM formed Al-Mg-Sc alloy exhibits the best mechanical properties after aging at 325℃/4h,with an average hardness of 152 HV₁,average yield strength,tensile strength and elongation after fracture of 521 MPa,551 MPa and 5.2%,respectively.After the Al-Mg-Sc alloy formed by SLM was annealed at500℃/8h,the mechanical properties of the samples were reduced to a certain extent,but the plasticity of the alloy was increased by 6.4%and205.7%compared with the printed state and the aged state,respectively.