Comparative Evaluation of the Mechanical Properties of Al–Si–Cu–Ni–Mg Alloys with Distinct Spatial Architectures at Ambient and High Temperatures

This study presents a comprehensive analysis of the mechanical properties of Al–Si–Cu–Ni–Mg piston alloys in both as-cast (AC) and as-extruded (AE) states, examining the microstructural configurations and their influence on mechanical properties ranging from ambient temperature to 350 °C. The AC alloy demonstrates a semi-continuous network distribution of secondary phases, in contrast to the dispersed particle distribution in AE alloy. A significant decrease in tensile and yield strengths with the temperature increasing is observed for both alloys. Notably, the AE alloy outperforms the AC alloy in tensile properties at ambient temperature, with ultimate tensile strength and elongation reaching 365 MPa and 12%, respectively. However, the AC alloy exhibits superior tensile strength at 250–350 °C. The study introduces the concept of failure rate (FR) to elucidate the temperature-dependent tensile strength reduction, revealing that the AC alloy maintains a lower FR compared to the AE alloy within the 250–350 °C range. The comprehensive analysis of strengthening mechanisms suggests that Orowan and thermal mismatch dislocation strengthening dominate at ambient temperature, while load transfer and network strengthening become predominant at elevated temperatures. These findings might provide critical insights into alloy performance optimization for high-temperature applications.