Effects of microstructure heterogeneity and defects on mechanical behavior of Zr modified AA7075 manufactured by laser powder bed fusion

Laser powder bed fusion of AA7075 is an ideal candidate for aerospace structures due to high structure design flexibility of the process and excellent strength-to-weight ratio of AA7075. Various inoculants have been incorporated into AA7075 to control solidification behavior and suppress hot cracks in literature, leading to notable microstructure heterogeneity, distinct defect characteristics and large scattering of mechanical performance. However, the way these microstructures and defects affect mechanical behaviors remains unexplored. The present work is devoted to decipher the correlation between microstructure/defects and mechanical properties of Zr modified AA7075 under as-built and T6 states. Tensile tests under different loading directions were performed with macroscale and microscale digital image correlation, showing anisotropy in ductility and inhomogeneous strain distribution across solidified melt pools. It is noteworthy that the T6 heat treatment significantly enhances the strength while maintaining the ductility of the as-built state. The ductility anisotropy is related to sharp lack-of-fusion defects, and the bypass of strength-ductility trade-off in the T6 state is induced by strain delocalization in coarse grain regions containing sharp defects and the suppression of dense submicron pores in fine grain zones.