Laser powder bed fusion of Zr-modified Al–Cu–Mg alloy: Crack-inhibiting, grain refinement, and mechanical properties

The application of laser powder bed fusion (L-PBF) in conventional high-strength wrought aluminum alloys is a significant challenge due to its high cracking sensitivity. In this study, 2024Al and 1.3-wt% Zr-modified 2024Al alloy deposits were prepared by L-PBF using pre-alloyed powder. The solidification cracking susceptibility of the 1.3-wt% Zr-modified 2024Al alloy was reduced to ∼0.4 of that of the 2024Al alloy. Compared to the complete columnar α-Al grain microstructure in the 2024Al deposit, the crack-free Zr-modified 2024Al deposit exhibited a heterogeneous grain structure having columnar α-Al grains in the inner region of the molten pool and ultrafine α-Al equiaxed grains at the fusion boundary. Based on the time-dependent nucleation theory and constitutional undercooling analysis ahead of solidification interface, the precipitation behavior of primary Al₃Zr nanoparticles is analyzed, and it is deduced that the high intensity of effective nucleation sites by nanosized primary Al₃Zr at the fusion boundary of molten pool leads to the formation of equiaxed grains at the beginning of the solidification of molten pool. The as-deposited Zr-modified 2024Al exhibited a yield strength (YS) of ∼376 ± 7 MPa and an ultimate tensile strength (UTS) of 441 ± 7 MPa with an elongation of 14.1 ± 1.6%. The YS and UTS increased to 402 ± 9 MPa and 483 ± 37 MPa after T6 heat treatment, respectively. Both the tensile properties of the as-deposited and T6-treated Zr-modified 2024Al were comparable to the wrought 2024-T651 alloy and higher than most of the previous L-PBFed Al–Cu–Mg alloys.