Influence of Cu content on the microstructure and high-temperature tensile and fatigue properties of secondary AlSi7Mg0.3VZr alloys

The effect of Cu content on the microstructure and high-temperature tensile and fatigue behaviours of heat-treated secondary AlSi7Mg0.3VZr alloys were evaluated. Thermodynamic calculations based on the CALPHAD method were carried out to evaluate the formation of different phases. Tensile and fatigue tests were performed at room temperature and high temperature (300 °C) on alloys that were solution treated at 485 °C for 24 h and artificially aged at 180 °C for 8 h. The results show that the addition of Cu significantly improved the room temperature tensile properties at the expense of ductility, thus decreasing the fatigue behaviour at lower stress amplitudes. At 300 °C, Cu-bearing precipitates were responsible for the AlSi7Cu3Mg0.3VZr alloy having a better thermal stability than the AlSi7Mg0.3VZr alloy, leading to higher tensile and fatigue properties. After increasing the testing temperature, the effect of casting defects on fatigue crack propagation decreased, thus reducing the scattering of data independently of the Cu content. The fatigue failure mode changed from brittle to ductile at 300 °C for both alloys