Material Properties and Structure of Al-Mg-Si Alloy Thin-Walled Profiles with Different Alloy Compositions and Aging Processes

Thin-walled Al-Mg-Si alloy profiles with different compositions and aging states were prepared using the heating and extrusion process. The properties and structure of the profiles were then investigated using a metallographic microscope, scanning electron microscope, projection electron microscope, and universal testing machine. The results show that the yield strength and tensile strength of the profile increases with the increase in total Mg + Si content, and ductility is reduced. If the total Mg + Si content is too high or too low, the crush performance of the material would decrease. Compared with the under-aged and near-peak-aged states, the three types of AI-Mg-Si alloy thin-walled profiles at the over-aged state have better effective energy absorption during crushing and higher bending angle; however, the tensile strength of the profile is optimal at the near-peak-aged state. The effects of alloy composition and aging process on material strength and crushing energy absorption are mainly attributed to the grain structure and differences in precipitation. For coarse grain structures, the grain boundary precipitate free zones are wider, which decreases the profile ductility. Simultaneously, an increase in primary strengthening phases in the grains would increase the profile strength.