An Al-Zn-Cr alloy with outstanding processability by laser powder bed fusion

The aim of this work is to investigate the processability of an Al-20Zn-0.1Cr (wt%) alloy by laser powder bed fusion (LPBF). With that goal, a wide range of processing parameter sets including laser power (P) values between 100 and 400 W and scan speeds (v) ranging from 100 to 1500 mm/s is utilized to manufacture cubic specimens using a pulse-laser source. These conditions comprise a very large range of volumetric energy density (VED) values, that span from 19 to 1111 J/mm³. Dense, crack-free, and isotropic polycrystalline microstructures are obtained for an extensive range of VED conditions. Despite the extremely large VED values achieved, the average grain size grows only moderately, and the formation of highly textured columnar grains is prevented. The origin of the crack-free and isotropic Al-Zn-Cr microstructures following LPBF processing is attributed to the high degree of segregation of Zn solutes and pure Zn particles to grain and cell boundaries, which bridge Al dendrites during solidification, as well as to the presence of Zn/Cr nanoparticles at the grain interiors, which also contribute to hinder grain boundary motion. Boundary pinning remains significant under high VED conditions as, despite the occurrence of Zn evaporation during processing, the amount of residual Zn significantly exceeds its room-temperature solubility. This work provides guidelines for the design of high strength Al alloys with extended processability via LPBF.