## 3 Results
### Crush-Performance Analysis
#### 3.1.2 Effect of Aging Process on Crushing Properties  
Figure 7 shows the displacement-load curves and crushing energy-absorption curves during axial crushing of the three Al-Mg-Si alloy thin-walled profiles in different aging states. The displacement value and duration at the first peak of the three specimen profiles of the displacement-load curve are close to each other, with only the peak size being different, after which the load peak gradually becomes disordered. In addition, all profiles have a high initial peak load, which reflects the ultimate-limit of structural load-bearing capacity of the thin-walled profiles. As shown in Table 2, the peak loads of profiles 6 xxx-1(1.6 Mg/Si), 6 xxx-2(1.33 Mg/Si), and 6 xxx-3(1.14 Mg/Si) in the near-peak-aged state are 402.75, 449.95, and 383.2 KN, respectively, which are greater than values in the under-aged  
Figure 5: The macro-morphology (near-peak-aged state) of the three Al-Mg-Si alloy thin-walled profiles after crush testing: (**a**) 6 xxx-1(1.6 Mg/Si) profile; (**b**) 6 xxx-2(1.33 Mg/Si) profile; (**c**) 6 xxx-3(1.14 Mg/Si) profile.  
Figure 6: Displacement-load curves and crushing energy-absorption curves during axial crushing of the three Al-Mg-Si alloy thin-walled profiles (at near-peak-aged state): (**a**) Displacement-load curves; (**b**) Energy-absorption curves.  
and over-aged states. The peak load change pattern of the profiles is the same as the change pattern of the mechanical properties, from which it can be presumed that mechanical properties are important factors affecting the peak load. In addition, the aging process has a significant effect on the final energy absorption of the profiles. If crack formation is not considered, the total crushing energy absorptions of the profiles are similar for the three aging processes. However, if only the effective crushing energy absorption is calculated, the under-aged and near-peaked-aged states would have significantly lower values than the over-aged state. Compared with profiles in the under-aged and near-peak-aged states, the effective crushing energy absorptions of profile 6 xxx-1(1.6 Mg/Si) in the over-aged state are higher by 35% and 81.8%, respectively; the effective crushing energy absorptions of profile 6 xxx-2(1.33 Mg/Si) in the over-aged state are higher by 129.1% and 314.3%, respectively; and the effective crushing energy absorptions of profile 6 xxx-3(1.14 Mg/Si) in the over-aged state are higher by 47.4% and 87.2%, respectively.  
Figure 7: Displacement-load curves and crushing energy-absorption curves during axial crushing of the three Al-Mg-Si alloy thin-walled profiles in different ageing states: (**a,c,e**) Displacement-load curves of profiles 6 xxx-1(1.6 Mg/Si), 6 xxx2, and 6 xxx-3(1.14 Mg/Si); (**b,d,f**) Energy-absorption curves of profiles 6 xxx-1(1.6 Mg/Si), 6 xxx2, and 6 xxx-3(1.14 Mg/Si).  
From Figure 7 and Table 2, the surface of profile of 6 xxx-1(1.6 Mg/Si) in the over-aged state is undamaged, and no crack formation is observed; the surface of profile 6 xxx-3(1.14 Mg/Si) in the over-aged state cracked slightly, but it does not have a significant effect on the applied load, whereas for profile 6 xxx-2(1.33 Mg/Si), cracks formed along the direction of the plastic hinge during compressive deformation for all aging states, which leads to a significant reduction in the applied load. In summary, in the over-aged state, profile 6 xxx-1(1.6 Mg/Si) has the best crush performance and absorbs the highest amount of energy during deformation.