A novel route for predicting the cracking of inoculant-added AA7075 processed via laser powder bed fusion

Solidification cracks caused by columnar grains in precipitation-hardenable Al alloys such as Al–Zn–Cu–Mg limits the applicability of laser-based additive manufacturing. Recently, cracking has been effectively reduced by introducing equiaxed grains through inoculant addition to Al alloy powder. However, the mechanisms through which equiaxed grains can prevent cracking have not been explained from the viewpoint of both microstructure and process parameters. Thus, the control over the cracking behavior of Al alloys during the laser powder bed fusion (LPBF) process has remained limited because of a lack of theoretical understanding. In this study, a solidification cracking model was proposed using the parametric LPBF results of ZrH2 particle-added AA7075, where equiaxed grains were formed as a function of energy density. In the proposed model, the cracks in the previously formed layer were healed by liquid backfilling during remelting under appropriate solidification conditions. The synergistic effects of both repeatable melting (layer-by-layer) and equiaxed grain formation on the cracking behavior were revealed. Consequently, the proposed model opens a novel route to cracking prevention in laser-based metal additive manufacturing processes.