Designing Al alloys for laser powder bed fusion via laser surface melting: Microstructure and processability of 7034 and modified 2065

Abstract

Age-hardenable 2000- and 7000-series aluminium alloys share the ability to achieve outstanding combinations of high specific strength and fracture toughness without including expensive alloying elements such as scandium. Using laser surface melting (LSM), we investigate the suitability of two commercial, high-strength aluminium alloys (ultimate tensile strength ≥ 600 MPa) for laser powder bed fusion (L-PBF). It is revealed that solidification cracks form in both, the third-generation Al-Cu-Li alloy 2065 and the high-Zn containing alloy 7034, with the latter having a lower crack density. Through a combination of microstructural characterisation by SEM, EDS, and EBSD, residual stress analysis and quantitative hot cracking criteria, we deduce that alloy 2065 shows greater potential for L-PBF application despite its slightly higher crack density after LSM. Through laser surface alloying, the composition of alloy 2065 was systematically varied in terms of titanium and copper content to improve its cracking resistance. It is found that the formation of solidification cracks is suppressed by the addition of 2 – 4 wt% Ti, whereas the introduction of copper has little effect. Our study suggests that Ti-modified 2065 is an attractive alloy for L-PBF. It could potentially join the existing high-strength aluminium feedstock materials available for L-PBF.