Effect of heat treatment on the microstructure and mechanical properties of Al‐9Si‐0.4Mg‐0.1Cu alloy

In this work, effect of heat treatment on the microstructure and mechanical properties of a newly developed Al-9Si-0.4Mg-0.1Cu alloy treated by Al-6Sr-7La was investigated, and optimal T6 heat treatment process parameters were determined through optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis and quantitative statistics. The results showed that the distribution of α-Al was more uniform after T6 heat treatment (solution treated at 540°C for 5h and aged at 170°C for 6h) with eutectic silicon possessing fine grain and high roundness. Meanwhile, Al-6Sr-7La increased peak aging hardness and reduced peak aging time. Dislocations provided diffusion channels for solute atoms, resulting in a large number of uniformly distributed Mg5Si6 strengthening phases precipitated during aging process. During under-aging process, a large amount of GP zone and a small amount of Mg5Si6 phase precipitated which had strengthening effect on the alloy. At peak aging state, coherent precipitated Mg5Si6 phase in α-Al lead to the highest micro-hardness. Continuing to prolong aging time, coherent relationship between metastable phase Mg5Si6 and the matrix was weakened, resulting in the decrease of micro-hardness. In addition, after T6 heat treatment, both tensile strength and elongation of the alloy were significantly improved and the reasons were discussed. This article is protected by copyright. All rights reserved.