Synergistic effect of Zr and Mo on precipitation and high-temperature properties of Al-Si-Cu-Mg alloys

This study focuses on finding a solution to the sharp decline in mechanical properties of Al-Si-Cu-Mg alloys due to rapid coarsening of traditional intermediate phases at high temperature. A new type of modified alloy, to be used in automobile engines at high temperatures, was prepared by adding Zr and Mo into Al-Si-Cu-Mg alloy. The synergistic effects of Zr and Mo on the microstructure evolution and high-temperature mechanical properties were studied. Results show that the addition of Zr and Mo generates a series of intermetallic phases dispersed in the alloy. They can improve the strength of the alloy by hindering dislocation movement and crack propagation. In addition, some nano-strengthened phases show coherent interfaces with the matrix and improve grain refinement. The addition of Mo greatly improves the heat resistance of the alloy. The extremely low diffusivity of Mo enables it to improve the thermal stability of the intermetallic phases, inhibit precipitation during aging, reduce the size of the precipitates, and improve the heat resistance of the alloy.