Study about heat treatment on microstructure, electrical conductivity and mechanical properties of Al-1Si-0.6Mg-0.2Fe alloy

Abstract

In this study, the electrical conductivity (EC) and mechanical properties of extruded state Al-1Si-0.6Mg-0.2Fe alloy (ES-Alloy) are enhanced through T6 heat treatment, and the underlying mechanisms are analyzed in conjunction with model calculations. Results demonstrate that the optimal heat treatment process for the ES-Alloy is 550 °C / 2 h + 230 °C / 16 h. Through the heat treatment process, the alloy’s EC and ultimate tensile strength are 57.0% IACS and 247.6 MPa, respectively, which are improved by 4.6% and 54.8%, respectively. For ES-Alloy, after heat treatment, owing to reversion and recrystallization, the average grain size of the alloy is 175.9 μm and becomes 6.93 times larger. Combined with theoretical calculation, the contribution of grain boundary strengthening to the alloy's strength is only reduced by 9.1 MPa. However, the reduction of grain boundary area reduces the scattering of free electrons during the transport process, which is beneficial to improving EC. Moreover, by modifying the heat treatment parameters, nanoscale Mg2Si and large-size AlFeSi second phases present in the alloy keep a favorable lattice match with the Al matrix, proving that this makes the main contribution to the alloy’s strength. The microstructures give consideration for both the high efficiency of electron transport and the enhancement of mechanical properties. So, it is advantageous for the improvement of EC and mechanical properties.