Microstructures and aging characteristics of Al-Mg-Sc alloy fabricated by selective laser melting

We investigated the processability and aging characteristics of a selective laser melted (SLM) Al-Mg-Sc alloy. The Al-Mg-Sc SLM specimens were densified with increasing volume energy density in the SLM process. The Al-Mg-Sc SLM specimen, fabricated under the optimum laser scan conditions for densification, had a relative density of more than 99.9%. The Vickers hardness significantly increased by aging heat treatment, and the peak-aging condition was found at 325 °C for 4 h. Meanwhile, the hardness could be maintained even after prolonged aging, that is, robust aging behavior was confirmed for aging time. Both the as-fabricated and peak-aged Al-Mg-Sc SLM specimens showed mixed crystal grain microstructures with equiaxed and columnar crystals. The nanostructure of the peak-aged Al-Mg-Sc SLM specimen was dispersed single-nano-sized Al3Sc precipitates in the α-Al matrix, which were generated by aging of the as-fabricated SLM specimen supersaturated with solid solution Sc. In the peak-aged Al-Mg-Sc SLM specimen, both the tensile strength and 0.2% proof stress significantly increased to 550 MPa and 500 MPa, respectively, equivalent to those of the heat-treated conventional extra-super duralumin. This strengthening was mainly attributed to precipitation hardening of the finely precipitated Al3Sc phase (L12-type), coherent with the α-Al matrix.