Facile and cost-effective approach to additively manufacture crack-free 7075 aluminum alloy by laser powder bed fusion

It is an often challenging but essential issue to develop a facile and cost-effective approach to additively manufacture crack-free and high-strength Al alloys for their wider commercial applications. However, efficient synergistic combination of advanced technology and material development is hardly likely to achieve without considering the extreme processing conditions during additive manufacturing. In this study, the addition of 4 wt% Ti-6Al-4V (TC4) alloy powders, the most commercially used Ti alloy powders, into the laser powder bed fusion (L-PBF) of 7075 Al alloy was performed and experimentally verified to be capable of eliminating the hot cracks while substantially refining the grains. The as-printed sample was crack-free and had a high relative density of up to 99.95%. Synergy effect of the in-situ formation of Al3(Tix,V1−x) particles that act as the heterogeneous nucleation sites, and the solute effect of the elements Ti and V that possess a high grain growth restriction factor (Q value) in Al matrix can efficiently control the grain growth. After a direct ageing treatment, the resultant alloy displayed an excellent combination of the high ultimate tensile strength (441 ± 3 MPa) and large plasticity (10.1 ± 0.4%). Our work brings new insights between the grain refinement and crack elimination of additively manufactured Al alloys through addition of commercial Ti alloys, benefiting the tailoring and development of new crack-free and dense high-strength Al alloys for L-PBF.