Microstructure and mechanical properties of a novel selective laser melted Al–Mg alloy with low Sc content

The novel Al-4.5Mg-0.32Sc-0.66Zr alloy was successfully fabricated by selective laser melting. The minimum porosity of 0.5% was obtained for a laser power of 180 W, a scan speed of 220 mm s−1 and a hatch distance in the range of 0.13–0.15 mm. The microstructure of the as-fabricated alloy consists of aluminum solid solution grains with a typical bimodal size distribution at about 3–5 μm and 1 μm. Nanosized Al3(Sc, Zr) particles with a size of about 20–50 nm mainly formed on grain boundaries after one stage annealing at 360 °C/6 h. Homogenously distributed Al3(Sc, Zr) dispersoids 5–8 nm in diameter formed after two stage annealing 300 °C/3 h + 360 °C/4 h. As result the plasticity is 6% higher after two-stage annealing than after one-stage annealing. The yield strength and the ultimate tensile strength after both heat treatments are 424–438 MPa and 465–480 MPa, respectively. The optimum strength and plasticity combination was obtained after two-stage annealing in the samples fabricated in the XY direction: YS = 435 MPa, UTS = 478 MPa and El. = 16%.