On the microstructures and properties of a Zr-modified Al-Si-Cu-Mg alloy at intermediate temperature

In this study, the mechanical properties of an Al-Si-Cu-Mg alloy at intermediate temperature (100-200 degrees C) are improved by adding trace amounts of Zr, which can effectively inhibit its nucleation and grain growth and refine the grains. The experimental results show that the eutectic Si microstructures of the alloy are refined after adding Zr and the size of the Fe-rich phase is decreased. The maximum tensile strength of the heat-treated alloy with 0.2 wt% Zr is 442.3 MPa and the elongation is 2.77 %. The microstructure of the alloy evolved under the intermediate-temperature heat-affected environment. With a thermal exposure time from 20 to 100 h, the microstructural distribution is more dispersed and the strength decreased sharply. After 100 h of thermal exposure, the strength and elongation of the alloy are 155.7 MPa and 6.67 %, respectively. It is found by TEM that the thermally stable Al3Zr phase is formed in the alloy that did not decompose under the influence of intermediate temperature for a long period. The coarsening of Al2Cu is the reason for the decrease in the mechanical properties in the intermediate-temperature environment. The interface matching between L12-Al3Zr is established using first-principles calculations. The results show that the interface between Al3Zr and the matrix is well bonded and L12-Al3Zr is an effective alpha-Al heterogeneous nucleating agent.