A Phenomenological Study of the Influence of Temperature and Strain Rate on the Fracture Behavior of Double-Sided Laser-Welded Al-Mg-Si Alloy Butt Joint
摘要
Aluminum 6XXX series alloys are widely used in the automotive industry for their strength, formability, and corrosion resistance. Double-sided welds are commonly applied in tailor-welded blanks, which could form the welded material at elevated temperatures. This study examines the fracture behavior of double-sided welded Al6061-T6 under tensile load at temperatures ranging from room temperature to 200 °C and different strain rates of 0.1-0.01 s-1. The microstructure of the laser-welded area reveals two fusion zones situated in the upper and lower regions of the joint, with an H-shaped heat-affected zone (HAZ). The central portion of the HAZ, which separates the two fusion zones, displays a distinct microstructure compared to other sections of the HAZ. This area consists of small recrystallized grains, which exhibit microcracks around the grain boundaries. The results show that increasing temperature from room temperature to 200 °C leads to a significant reduction in UTS and yield strength, while strain and energy absorption increase with temperature. Strain-rate sensitivity, within the quasi-static range of 0.01-0.1 s−1, is minimal, with negligible impact on UTS and energy absorption, suggesting that these properties remain stable across this range. However, strain rate has a noticeable effect on yield stress and fracture strain, with lower strain rates resulting in higher fracture strain and lower yield stress. Statistical analysis confirms these findings, indicating that temperature is the dominant factor influencing mechanical properties, while strain rate has a lesser impact. Fractography analysis reveals that at temperatures exceeding 150 °C, microcracks in the fusion zone act as crack initiation sites. In contrast, at lower temperatures, crack initiation is more sensitive to geometrical defects in the heat-affected zone.