To achieve a combination of high strength and high thermal conductivity in cast aluminum alloys, this study employed commercial pure Al, Al-20%Si master alloy, and pure Mg as raw materials to prepare Al-Si-Mg alloys with varying Mg contents via permanent mold gravity casting. The effects of Mg content on the microstructure and properties of Al-Si-Mg alloys were systematically investigated using optical metallographic microscope, scanning electron microscope, transmission electron microscope, microhardness tester, digital electrical conductivity meter, universal tensile testing machine, and laser flash thermal conductivity meter. The results demonstrate that increasing Mg content refines the α-Al dendrites with the secondary dendrite arm spacing decreasing from 17.77 μm to 15.16 μm. Meanwhile, the formation of Mg2Si phases is promoted, and their morphology transitions from skeletal to particulate as the Mg content increases. After peak aging treatment at 190 ℃ for 8 h, the precipitation of nanoscale β″ phase provides significant strengthening effects, concurrently leading to a notable improvement in thermal conductivity. The peak-aged Al-6Si-1.0Mg alloy exhibits optimal comprehensive properties with tensile strength, yield strength, elongation, and thermal conductivity reaching 318.6 MPa, 176.2 MPa, 6.24%, and 190.7 W/(m·K), respectively. By regulating the Mg content and aging process, this study achieves a balance between strength and thermal conductivity in Al-Si-Mg alloys.
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