加载路径对5A06铝合金力学性能和微观组织的影响

目的 通过力学性能测试和微观组织表征等手段研究预加载方向和双向加载对5A06铝合金组织性能的影响。方法 分别沿轧制方向(RD)和垂直于轧制方向(TD)施加预变形，然后沿RD进行拉伸试验，对比研究预加载方向对合金力学性能的影响。通过双向拉伸试验研究合金在双向加载时力学性能的变化情况;采用透射电镜观察预加载和双向加载条件下典型试样内的位错组态，分析加载路径对位错组态的影响。结果 预加载使5A06铝合金的屈服强度提高，伸长率下降。与RD预加载相比，TD预加载对屈服强度和伸长率的影响更小，TD预加载试样的抗拉强度更高。不同预加载方向下试样的位错组态不同:预加载与二次加载方向一致会使位错沿单一方向塞积;预加载与二次加载方向垂直时会出现平行位错列交错缠结现象。双向加载时，不同加载比例下合金的应力–应变关系不同，加载比例越接近等比例双向拉伸情况，加工硬化系数越大，在等比例双轴拉伸时达到最大。在应力状态从单拉状态变化到等双拉状态的过程中，不同阶段屈服点间隔不同，在等比例双轴拉伸时达到最大，在单向拉伸时最小。对于不同加载比例的试样，其位错密度随中心区应变量的增大而增大。结论 预加载方向会显著影响5A06铝合金的力学性能和位错组态。不同比例的双向加载会影响5A06铝合金的应力–应变关系。

Effects of Loading Paths on Mechanical Properties and Microstructure of 5A06 Aluminum Alloy

The work aims to study the effect of pre-loading direction and biaxial loading on the properties of 5A06 aluminum alloy through mechanics performance testing and microstructure characterization. The specimen was pre-deformed in the axial direction (rolling direction, RD) and the transverse direction (TD), and then stretched along RD to compare the effects of pre-loading direction on the mechanical properties of the alloy. The mechanical property change of the alloy under biaxial loading were studied by biaxial tensile test. The through transmission electron microscope (TEM) was used to observe the dislocation configuration in typical specimen under pre-loading and biaxial loading and analyze the effects of loading path on dislocation configuration. Results showed that pre-loading improved the yield strength of 5A06 aluminum alloy and decreased its elongation. Compared with pre-loading in RD, pre-loading in TD had less effects on the yield strength and elongation. The tensile strength of specimen with pre-loading in TD was slightly higher than that of pre-loading in RD. Specimen under different pre-loading directions had different dislocation configuration. When the pre-loading direction was the same as the subsequent loading direction, the dislocations mainly packed along one direction, while for the specimen which had different pre- and subsequent loading directions, the intertwined dislocation entanglement were observed in the specimen. The stress-strain relationship of 5A06 aluminum alloy under different loading paths was different. As the loading ratio approached to equal, the work hardening coefficient increased, and it was the highest when the loading was equal in two directions. As the stress state changed from single tension to equal double tension, the interval of yield point was different at different stages, the equal tension state showed the largest, and the single tension state showed the smallest. For specimen with different loading ratios, the dislocation density increased with the increase of strain in the central region. These results indicate that the pre-loading paths can significantly affect the mechanical properties and the dislocation configuration of 5A06 aluminum alloy. The results of this study can provide a theoretical basis for the forming process design and performance prediction of aluminum alloy components. Biaxial loading of different proportions will affect the stress-strain relationship of 5A06 aluminum alloy.