Effect of Heat Treatments on Microstructure and Mechanical Properties of AlSi7Mg Fabricated by Selective Laser Melting

To obtain aluminum alloy with better mechanical properties, it is necessary to investigate the influence of process parameters and different heat treatments on the microstructure and mechanical properties of AlSi7Mg fabricated by SLM (Selective Laser Melting). The microstructure of the specimens under as-built, annealing as well as solution and aging conditions were studied by OM, SEM and EDS. The tensile properties were tested with a tensile test machine, and the tensile fracture morphology was investigated by SEM. The results showed that the maximum relative density of the specimens reached 99.8%. The tensile strength of the specimens after annealing and solution all decreased compared with as-built specimens (435.78 MPa). With the annealing temperature increasing, the tensile strength all decreased (from 304.28 to 210.35 MPa), while elongation increased (from 14.45 to 30.83%). With the solution temperature increasing, the tensile strength and elongation increased at first and then decreased (the maximum was 349.27 MPa and 17.12%). The fracture mode of as-built specimens was a mixture of brittle and ductile fracture. The fracture morphology of the heat-treated specimens presented big and deep dimples, which indicated a ductile mode.