汽车用2024-T351铝合金的动态力学行为各向异性

Anisotropy of Dynamic Mechanical Behavior of 2024-T351 AluminumAlloy for Automobile

采用拉伸机、扫描电子显微镜(SEM)及光学显微镜(OM)等研究了汽车用2024-T351铝合金的动态力学行为各向异性与微观组织演变。结果表明,2024-T351铝合金表现出明显的各向异性且应变率对力学性能与微观组织有一定的影响。相同应变率下,0°方向上的应力最大,45°方向上的应力最小。在0°方向上,合金的抗拉强度随应变率的增加变化相对较小,而屈服强度、延伸率和断面收缩率呈现先增加后保持不变最后持续增加的趋势;在45°和90°方向上,合金的抗拉强度、屈服强度、延伸率与断面收缩率均随着应变率的提高呈现先增加后保持不变最后持续增加的趋势;90°方向相比于其他两个方向有着更强的应变率敏感性。拟合得到三个方向上的Johnson-Cook本构方程,其可以很好地预测2024-T351铝合金在各个方向上的动态力学行为。所有试样断口表面均有大小不一的韧窝,且应变率越高形成的韧窝就会越大且越深。断后晶粒尺寸与方向和应变率基本无关,但晶粒纵横比受方向和应变率的影响较大。

The dynamic mechanical behavior and microstructure evolution of the 2024-T351 aluminum alloy used in automobiles were investigated using a tensile testing machine, scanning electron microscope (SEM), and optical microscope (OM). The results showed that the 2024-T351 aluminum alloy exhibited significant anisotropy, and the strain rate had a certain influence on the mechanical properties and microstructure. Under the same strain rate, the stress was highest in the 0° direction and lowest in the 45° direction. In the 0° direction, the ultimate tensile strength of the alloy changed relatively little with increasing strain rate, while the yield strength, elongation, and reduction of area showed a trend of increa- sing first, then remaining constant, and finally increasing continuously. In the 45° and 90° directions, the ultimate tensile strength, yield strength, elongation, and reduction of area all showed a trend of increasing first, then remaining constant, and finally increasing continuously with increa- sing strain rate. The 90° direction had a stronger strain rate sensitivity than the other two directions. Johnson-Cook constitutive equations were fitted for the alloy in the three directions, which could well predict the dynamic mechanical behavior of the 2024-T351 aluminum alloy in various directions. All specimen fracture surfaces had variable-sized dimples, and the dimples formed at higher strain rates were larger and deeper. The grain size after fracture was basically unrelated to the direction and strain rate, but the aspect ratio of the grains was greatly influenced by the direction and strain rate.