Effect of Heat Treatment on Mechanical Properties and Fracture Behavior of Al-7.0Si-0.3Mg Alloy at Low Temperature

Abstract

In order to investigate the effect of heat treatment on the mechanical properties of the Al-7.0Si-0.3Mg alloy at 20–60 °C under different heat treatment processes, the tensile mechanical properties of Al-7.0Si-0.3Mg at low temperature after heat treatment were explored. The microstructure of Al-7.0Si-0.3Mg was observed by scanning electron microscopy (SEM) and transmission electron microscopy. The results show that the resistance of the dislocation movement in α-Al increased in the low-temperature condition, which is beneficial for the number of Si phase fractures that increase to enhance the tensile strength and weaken the elongation of the Al-7.0Si-0.3Mg alloy. After the solution treatment, the particle size of the Si phase reduced, while the morphology became rounded. In the early stage of aging, a GP region is generated inside the α-Al. With the prolonging of aging time, the acicular β″ phase is formed and then grows into rod-shaped β′. In the overaging stage, β′ eventually grows into flaky β. Due to the different linear expansion coefficients of the α-Al and the Mg2Si phase in the Al-7.0Si-0.3Mg alloy, the α-Al is squeezed by the Mg2Si phase under the effect of low-temperature shrinkage.