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

Abstract

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 μm to 0.564 μm 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.