Laser powder bed fusion of nanoparticle-enhanced sustainably-manufactured AA7075 alloy

High-strength aluminum alloy series are prone to solidification cracking during the laser powder bed fusion (LPBF) additive manufacturing (AM) process. As such, poor printability continues to hinder the industrial use of LPBF-processed high-strength aluminum alloys. Addition of appropriate nanoparticles is known as an effective solution to prevent solidification cracking through heterogenous nucleation of equiaxed grains. On the other hand, the presence of nanoparticles influences laser-material interactions, making it more challenging to achieve high relative density parts. In this study, 1 vol.% ZrH2 nanoparticles were added to a low-cost, environmentally sustainable AA7075 aluminum alloy powder with a non-equiaxed morphology. The powder morphology differs from the conventional spherical powders typically used in AM and will further influence the final relative density. To systematically study the melting mode behavior of AA7075+ZrH2 (7A76) alloy, a normalized processing diagram coupled with a temperature prediction model was employed. Results indicated that the relative density of the alloy is greatly dependent on the melting mode behavior. Transition melting mode was found to be effective in minimizing elemental evaporation of Mg and Zn and achieving a defect-free 7A76 with a relative density of 99.98%. This reported relative density is the highest achieved in literature to date. Furthermore, partially-melted nanoparticles were found in the microstructure, which act as nucleation sites, participating in the crack prevention mechanism.