Effect of over-aging on the microstructure, mechanical properties and crashing performance of thin-walled Al–Mg–Si–Cu alloy profiles

Abstract

The thin-walled Al–Mg–Si–Cu alloy (AA6008) crash-box profiles were treated by over-aging at 215 °C for 60 min, 120 min and 300 min, and then their corresponding microstructure, mechanical properties, and crashing performance were investigated. The results show that with the increase of aging time, the number density of precipitation is decreased significantly, the size of precipitate is coarsened, and the precipitate type is transformed from β″ to β′, resulting in a reduction of microhardness and strength. The crashed morphology of the profile is improved showing a more regular folding deformation and less crack, but the corresponding values of energy absorption and mean crash force are decreased owing to the decrease of the strength. The medium overaged treatment, i.e., AA 215 °C-120 min sample, can obtain a balanced combination of excellent mechanical properties (yield strength > 280 MPa) and crashing performance. The influence of precipitation on the mechanical properties and crash deformation is also discussed based on experimental results.