Effect of temperature on the mechanical properties of Al-Si-Cu-Mg-Ni-Ce alloy

High-temperature performance is a key factor to concern for the application of cast Al-Si alloys. The evolution of microstructures and mechanical properties of a multiphase Al-Si-Cu-Mg-Ni-Ce alloy during tension in a temperature range from 25 degrees C (ambient temperature) to 425 degrees C was investigated. The results show that the main strengthening precipitates of the alloy are theta' and Q phases. They are stable at 25-250 degrees C, while dissolve rapidly above 250 degrees C during tension. The damage initiates and propagates in the form of cracking of brittle phases. The fracture mechanism transforms from quasi-cleavage to coexistence of quasi-cleavage and dimple as temperature increases. The Ce-bearing phase Al20Ti2Ce promotes the damage occurrence below 350 degrees C while hinders crack propagation at 425 degrees C. The ultimate tensile strength (UTS) and yield strength (YS) decrease as the tensile temperature increases. The decreasing rate of UTS can be divided into three stages which is associated with the decreasing rate of strengthening precipitates. An empirical constitutive equation is proposed to describe the relationship between UTS and tensile temperature. It provides a good estimation for both cast and wrought Al alloys and the predicted strengths are in good agreement with the experimental results.