Balancing the strength-toughness synergy and crushing behavior of 6082 aluminum alloy crash boxes via double-stage aging regulation

Al–Mg–Si alloy automotive crash boxes often necessitate a compromise in strength to achieve the high toughness required for deformation stability. This inverse relationship between strength and toughness constitutes a critical bottleneck that restricts improvements in crashworthiness. This study investigates a double-stage aging (DSA) protocol (160 °C-9 h + 205 °C-4 h) and systematically compares it with traditional single-stage peak aging (PA) and over-aging (OA) treatments. The findings reveal that the DSA process maintains the alloy's high strength while utilizing the second-stage high-temperature aging to promote moderate matrix recovery. This reduces the Kernel Average Misorientation (KAM) value from 1.27° in the peak-aged state to 0.95°, effectively mitigating stress concentration at grain boundaries and thereby achieving an exceptional strength-toughness balance. Furthermore, in contrast to the severe corner cracking observed in peak-aged crash boxes during crushing, the DSA-treated crash boxes manifest a stable, progressive folding mode without severe cracking. The bending angle reached an outstanding 152.94°, representing an 11.0% improvement over the over-aged state, while the tensile strength was maintained at a high level of 275.99 MPa, and the total energy absorption during crushing increased by 3.39%. Additionally, tensile tests revealed a significant positive correlation between the relative instability elongation during the local necking stage and the crushing failure behavior of the crash boxes.