Microstructure evolution and comprehensive properties of the extruded AA6008 crash-box profiles aged at 210 °C–220 °C

The AA6008 Al alloy crash-box profiles were artificially aged at 210, 215 and 220 °C for 120 min, and the corresponding microstructure, mechanical properties and crashing performance were investigated. The results show that as the aging temperature increases, the average number density of precipitates decreases and their sizes (average length and diameter) become coarser, resulting in a significant decline in the microhardness and strength of the profiles. Meanwhile, the ductility and toughness in AA6008 profiles are enhanced, showing an increase of 14.8 % in the bending angle and a raise of 17.7 % in the crack unit initiation energy. As a result, the crashed morphology of the AA6008 profile is improved, while the energy-absorption characteristics are decreased owing to the decrease of strength. The AA6008 aged at 220 °C (AA220°C-120min sample), with a yield strength of 271 MPa, exhibits an excellent crashing performance, which is mainly related to coarse precipitates with a low number density.