Microstructural stability and high-temperature mechanical behavior of Al–Ni–Zr alloy strengthened by L1▫$_2$▫-Al▫$_3$▫Zr precipitates

Aluminum alloys based on the eutectic Al–Ni system are a promising class of lightweight materials for applications at elevated temperatures owing to the thermal stability of the eutectic Al▫$_3$▫Ni phase. In this study, the eutectic Al–Ni alloy was modified by the addition of 0.6 wt.% Zr to enhance the αAl matrix by precipitation strengthening. The alloys were cast and subjected to T5 heat treatment followed by long-term isothermal aging at 350 ◦C. A comprehensive study was carried out to evaluate the evolution of microstructure, micro-hardness and mechanical performance over time. The formation of fine, coherent L1▫$_2$▫-Al▫$_3$▫Zr precipitates contributed to significant strengthening, as reflected by a ~60% increase in microhardness and an approximately twofold improvement in room temperature (RT) yield strength. A TEM analysis of the L1▫$_2$▫-Al▫$_3$▫Zr precipitates showed relatively good thermal stability after 30 days. Despite the improved mechanical properties at room temperature, the alloy did not retain this improvement when tested at 300 ◦C. Nevertheless, these results provide a comprehensive insight into the aging and thermal stability of Al–Ni–Zr alloys.