Effects of solute supersaturation and re-precipitation on microstructure and mechanical properties of selective laser melted Al−Mn−Mg−Sc−Zr alloys

A new Al−4.87Mn−1.42Mg−0.63Sc−0.20Zr (wt.%) alloy was fabricated by selective laser melting (SLM) and its microstructure and mechanical properties before and after aging were investigated. The results show that at a laser power input of 300 W, increasing laser scanning speeds from 700 to 1500 mm/s improves the mechanical properties. In the meantime, the lattice distortion values increase from 0.15% to 0.31%, showing an increasing solute supersaturation. At a laser scanning speed of 1500 mm/s, the yield strength, ultimate tensile strength and elongation of the as-SLM alloys are 356 MPa, 412 MPa and 17.7%, respectively. After aging at 350 °C for 8 h, these values increase to 527 MPa, 554 MPa and 10.4%, respectively. The contributions to the yield strength increments from the secondary Al₆(Fe, Mn) needle-like phase and re-precipitated L1₂ structured Al₆(Sc, Zr, Ti) nano-particles during aging are 74 and 79 MPa, respectively. As the aging temperature increases to 450 °C, the dominant precipitation strengthening is attributed to the secondary Al₆(Sc, Zr, Ti) nano-particles.