Effect of Solution Treatment on the Hardness and Tensile Properties of Al-Mg-Si Alloys for Automotive Chassis

Al-Mg-Si alloys, which are used mainly as wrought materials, can also be used as casting materials because of the development of casting technologies. To improve the mechanical properties of alloys, the casting materials are often subjected to different heat treatments. Therefore, the influence of heat treatment on the mechanical properties of aluminum alloys needs to be understood before wrought alloys can be used in automotive casting components. This study examined the effects of solution treatment on the microstructure and mechanical properties of casting Al-Mg-Si alloy for automotive chassis. After a solution treatment for 5 and 8 h at 535 to 565 degrees C, the microstructures were examined depending on the heat treatment temperature and time by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. As a result, Al matrix, beta-Al5FeSi and Mg2Si phases were observed in solution-treated Al-Mg-Si alloys. In addition, the solution treatment temperature and time had a significant effect on the hardness and tensile properties of the alloy. The hardness and tensile strength increased with increasing solution treatment temperature to 555 degrees C due to the solid solution hardening with the dissolution of residual phases. In contrast, when the solution temperature increased further to 565 degrees C and the solution treatment time was increased, the hardness and the tensile strength decreased due to softening by grain growth rather than the effects of the solid solution hardening. In addition, the uniformity of the mechanical properties by each location of the specimen increased with increasing solution treatment duration due to the increase in time needed to produce a sufficient solid solution.