Microstructures and mechanical properties of A356 (AlSi7Mg0.3) aluminum alloy fabricated by selective laser melting

Optimum laser irradiation conditions to achieve dense A356.0 (AlSi7Mg0.3) specimens fabricated by selective laser melting (SLM) were studied. The SLM specimens with relative density of 99.8% were obtained. The microstructures and mechanical properties of the dense SLM specimens fabricated under the optimum laser irradiation conditions were also investigated. The dense SLM specimens had an ultimate tensile strength, yield strength, and breaking elongation of 400 MPa, 200 MPa, and 12–17%, respectively. All of these values considerably exceeded those in cast-melting materials. The superior mechanical properties of the SLM specimens could be attributed to fine dendritic cell microstructures and relative density of almost 100%. An investigation of the heat treatment effects on the microstructures and mechanical properties revealed a clear difference in annealing behaviors between the SLM specimens and the cast-melting materials. After annealing (T5), the breaking elongation of the SLM specimen increased from 15% in the as-fabricated specimen to 30% in the specimen annealed at 350 °C, while the ultimate tensile strength and yield strength decreased from 400 MPa and 250 MPa to 200 MPa and 125 MPa, respectively. This confirmed that the mechanical properties of the SLM specimens could be controlled in accordance with required functions for design.