Microstructural Stability and High-Temperature Mechanical Behavior of Al-Ni-Zr Alloy Strengthened by L12-Al3Zr 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 Al3Ni phase. In this study, the eutectic Al-Ni alloy was modified by the addition of 0.6 wt.% Zr to enhance the alpha(Al) matrix by precipitation strengthening. The alloys were cast and subjected to T5 heat treatment followed by long-term isothermal aging at 350 degrees C. A comprehensive study was carried out to evaluate the evolution of microstructure, microhardness and mechanical performance over time. The formation of fine, coherent L1(2)-Al3Zr precipitates contributed to significant strengthening, as reflected by a similar to 60% increase in microhardness and an approximately twofold improvement in room temperature (RT) yield strength. A TEM analysis of the L1(2)-Al3Zr 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 degrees C. Nevertheless, these results provide a comprehensive insight into the aging and thermal stability of Al-Ni-Zr alloys.