Microstructure characterization and mechanical properties of crack-free Al-Cu-Mg-Y alloy fabricated by laser powder bed fusion

Additive manufacturing of high-strength Al alloys (such as 2xxx, 6xxx and 7xxx series alloys) by laser powder bed fusion (LPBF) encounters a challenge because of their high susceptibility to solidification crack. The current work develops a crack-free and novel high-strength Al-Cu-Mg-Y alloy fabricated by LPBF using the rare earth yttrium (Y) modified 2024 alloy powders. In the LPBF-fabricated Al-Cu-Mg-Y alloy, the rare earth element Y is revealed as an effective alloying element for the solidification crack elimination, which is mainly attributed to the combination of the narrowed brittle temperature range, the decreased solidification crack susceptibility index and the refined grains. The element Y can also react with Al and Cu to form the Al8Cu4Y phases during the LPBF process. In the LPBF-fabricated Al-Cu-Mg-Y alloy, the larger number of Al8Cu4Y phases and the finer grains result in higher compressive yield strength than most LPBF-fabricated Al alloys. Interestingly, the LPBF-fabricated Al-Cu-Mg-Y alloy can be highly deformed without collapse up to a large compressive strain of ~70 %. After T6 heat treatment, the LPBF-fabricated Al-Cu-Mg-Y alloy exhibits a significant increase in the compressive stress after the yield point, corresponding to the homogeneously distributed Ω precipitate in the Al matrix. In addition, the tensile strength is lower than the compressive strength for the LPBF-fabricated and T6 heat-treated Al-Cu-Mg-Y alloys. This difference is related to the internal pores in the two alloys.