High-strength additively manufacturable Al-Zr-Er-Ni alloys with high as-built ductility and thermal stability

Additively manufactured (AM) aluminum (Al) alloys with high as-built ductility offer sustainability, enhanced load-bearing performance, and resistance to residual-stress-induced failure. However, most commercial AM Al alloys have very limited ductility. In this study, the microstructural characteristics and damage micro-mechanisms of a benchmark alloy (Al-1.0Zr-0.4Er-1.3Ni at.%) was analyzed. Using SEM, we revealed that Al3Zr and Al3Ni accounted for 65% and 62% of cavity formation in as-built and heat-treated conditions, respectively. With calculation of phase diagrams (CALPHAD)-based integrated computational materials engineering (ICME) simulations, we found that at each Er concentration, Zr and Ni must not exceed thresholds required to act as reservoirs for the nano-meter scale L12 phase transformation (needed for high strength) during heat treatment. Following the guideline of Ni ≈ 0.6 % and Zr ≈ 1.1 × Er from simulations, an optimized composition of Al-0.5Zr-0.4Er-0.6Ni at.% was designed. The as-built ductility increases to 19% from 0.9% by only sacrificing 25% of strength to achieve 279 MPa. The strength is preserved even after 48 hours at 400 °C heat treatment.