Effect of Direct Ageing and Stress Relief Annealing on the Microstructure and Properties of Laser Selective Melting AlSi10Mg

In this work, we demonstrate the effects of direct ageing (DA) and stress relief annealing (SR) heat treatment on the microstructure evolution and residual stress changes of SLM formed AlSi10Mg alloys. The results show that the microstructure of the constructed AlSi10Mg alloy is mainly composed of α-Al and reticulated Si phases. Direct aging treatment promotes the precipitation of the nanophase and retains the reticulated Si structure, while the stress-relieving annealing destroys the reticulated Si structure, resulting in varying degrees of improvement in its mechanical properties. At 170 °C, 20% of the residual stress can be removed after 4 h, and the yield strength (YS) and ultimate tensile strength (UTS) of the alloy are 328 and 457 MPa, respectively, which are 38 and 7% higher than those in the forming state, and the elongation is slightly reduced. However, 60% of the residual stress can be removed by annealing at 400 °C for 2 h, but the yield strength (YS) and ultimate tensile strength (UTS) of the alloy are greatly reduced, which are 122 and 210 MPa, respectively, and the elongation is 16.8%.