A novel Si/Cu-modified Al-Mg alloy processed by laser powder bed fusion: Crack inhibition, microstructures and mechanical properties

The Al-Mg alloys fabricated via additive manufacturing normally suffer from poor printing ability and mechanical properties. Here, the cost-effective Si and Cu were used to modify an Al-5.5Mg alloy for laser-powder bed fusion (L-PBF), which achieved a synergetic combination of crack-free feature and high strength. It is found that the hot cracking was effectively eliminated in the L-PBFed samples due to the reduction of brittleness temperature range and the formation of fine Al-Mg2Si eutectics. A hierarchical structure featured by the refined ɑ-Al grains, sub-micron cellular structures decorated with Mg2Si, S-Al2CuMg nanoparticles and substantial dislocation networks was responsible for the obvious strength improvement in the L-PBFed Al-5.5Mg-2Si-Cu alloy, in which the ultimate tensile strength of 560 MPa, yield strength of 453 MPa and elongation of 9.1 % have been obtained. The synergistic effects of crack elimination and precipitation strengthening induced via the incorporation of Si/Cu provide the innovative guideline to fabricate crack-free Al-Mg alloys with high strength.