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.