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Herein, 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 is investigated, and optimal T6 heat treatment process parameters are determined through optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) analysis, and quantitative statistics. The results show that the distribution of α‐Al is more uniform after T6 heat treatment (solution treated at 540 °C for 5 h and aged at 170 °C for 6 h) with eutectic silicon possessing fine grain and high roundness. Meanwhile, Al–6Sr–7La increases peak aging hardness and reduces peak aging time. During the under‐aging process, a large amount of Guinier Preston zone and a small amount of Mg5Si6 phase precipitate, which have strengthening effect on the alloy. At peak aging state, the coherent precipitated Mg5Si6 phase in α‐Al leads to the highest microhardness. Continuing to prolong aging time, the coherent relationship between metastable phase Mg5Si6 and the matrix is weakened, resulting in the decrease in microhardness. In addition, after T6 heat treatment, both tensile strength and elongation of the alloy are significantly improved and the reasons are discussed.

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Al-0.5Mg-0.4Si-0.1Cu alloy possessing weather resistance and oxidation resistance can obtain good surface quality (metallic luster) without chrome plating. Therefore, it is an important material to replace polluting chrome-plated aluminum profiles for automotive decorative parts. At present, studies about the extrusion process of Al-0.5Mg-0.4Si-0.1Cu alloy are very few, which affects its further application. In this work, the effect of extrusion ratios on microstructure and mechanical properties of Al-0.5Mg-0.4Si-0.1Cu alloy is investigated by optical microscopy (OM), scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and tensile tests. The results showed that the dynamic recrystallization degree of the alloy gradually increased with the extrusion ratio increasing, which is attributed to the driving force provided by the large extrusion ratio. Meanwhile, due to the occurrence of dynamic recrystallization, the texture changed from <111> to <001> orientation. In addition, grains were obviously refined and uniform with the extrusion ratio increasing. Due to the fine grain strengthening mechanism, the tensile strength and elongation of the alloy with an extrusion ratio of 30 reached 152 MPa and 32.4%.