Enhancing Thermal Stability and High-Temperature Properties of Foundry Al Alloys through Zr and/or Er as Minor Alloying Elements

Abstract When designing structural parts made from foundry alloys for use at relatively high temperatures, it can be challenging to choose the “best” alloy or “best heat treatment” for a specific application. This is particularly true for age-hardenable Al–Si-based alloys. Many studies have focused on the role of minor elements in modifying silicon, the presence of second phases, precipitate formation, and how these factors affect the alloy’s mechanical properties. Analyzing microstructural changes during heat treatment can help us understand how the microstructure and properties evolve during high-temperature service. Based on this, the high-temperature stability at 400 °C of cast Al to which Zr and/or Er have been added is presented and discussed in the first part of the paper. The second part the paper focuses on the case of Zr and/or Er addition to an age-hardenable casting alloy of more complex composition: AlSi7Mg (A356 alloy). The role of these two elements during solidification, heat treatments and simulated service conditions was analyzed. Si modification by Er and grain refinement by Zr, the formation of additional intermetallic phases that reduced ductility and aging potential, the possible formation of intragranular particles during solution treatment at conventional temperatures for A356 alloy. The aim of the work is to point out the need to optimize the heat treatment process of as-cast parts to enhance the high-temperature performance age-hardenable Al alloys, considering the expected service conditions.