A new high strength Al–Mg–Sc alloy for laser powder bed fusion with calcium addition to effectively prevent magnesium evaporation

A precise control of the Mg content in Al–Mg alloys is essential to obtain predictable mechanical properties but the processing of Al–Mg alloys often suffers Mg losses due to Mg evaporation and oxidation. A new high strength Al–Mg–Sc alloy designed for LPBF (laser powder bed fusion) processing has been developed here, where Mg losses are effectively prevented by the addition of a low amount of calcium. A LPBF processing window which results in built parts with a 99.7% relative density and no detectable loss of Mg has been identified. The as-built microstructure of the new Calciscal® alloy, studied by transmission electron microscopy, is found to comprise areas of fine equiaxed grains and areas of coarser grains, with many Al4Ca precipitates present at the grain boundaries and within the coarser grains. After a subsequent ageing of 1 h at 375 °C, the tensile strength of Calciscal® is increased by 44% compared to the as-built condition and reaches 522 ± 2 MPa. The increase in strength observed in the heat-treated condition comes from the additional precipitation of numerous finely dispersed Sc-rich precipitates. This high strength, combined with a good ductility, makes Calciscal® competitive to other Al alloys and suitable for structural applications. Moreover, Calciscal® shows very reproducible tensile properties thanks to the Ca addition which leads to a better control and less variations of the Mg content in the alloy.