Crack-free high-strength AA-7075 fabricated by laser powder bed fusion with inoculations of metallic glass powders

High-strength aluminum alloy is widely utilized in aerospace field. The primary thrust of this work was to overcome the issue of hot cracking of AA-7075, which occurs during laser powder bed fusion (LPBF) processing. By employing an innovation inoculation treatment with 5 wt % Zr50.7Cu28Al12.3Ni9 metallic glass (MG) powders, highly dense (relative density >99.2 %) and crack-free composite specimens of AA-7075/MG were successfully fabricated within a broad printing range. The as-printed AA-7075/MG composite specimens exhibited a uniform microstructure with the fine equiaxed grains and the crack mitigation was attributed to the grain refinement, which decreased from 9.9 mu m to 0.564 mu m after addition of MG powders. The inoculation treatment of MG powders triggered the in-situ formation of Al3Zr particles on the one hand, promoting the formation of fine equiaxed grains with random orientation. On the other hand, in-situ formed nano-sized amorphous particles formed due to the high glass-forming ability of Zr-based MG and rapid cooling rate during LPBF process could strengthen the alloy. The as-printed AA-7075/MG composite specimens exhibited a compressive strength exceeding 1.5 GPa. Meanwhile, it exhibited the highest ultimate tensile stress and yield strength of 513 MPa and 488 MPa, respectively, with an elongation of over 9 %. The excellent mechanical properties are ascribed to a synergistic combination of grain boundary strengthening, precipitation strengthening induced by Al3Zr nanoparticles, solid-solution strengthening, and the effective obstacle of dislocation motion by the nano-sized amorphous particles. The current work presents a novel and cost-effective approach to producing crack-free, high strength aluminum engineering components using LPBF.