Ning Jian, Liang Jiangkai, Hu Xinyu, Ruan Xianggang, He Zhubin
State Key Laboratory of High-Performance Precision Manufacturing, School of Mechanical Engineering, Dalian University of Technology, Dalian 116024, China.
Materials (Basel). 2023 Jul 15;16(14):5012. doi: 10.3390/ma16145012.
The 2195 Al-Li alloy, as one of the representative third-generation Al-Li alloys, has extensive applications in lightweight aerospace structures. In this paper, the anisotropy in mechanical properties and microstructure evolution of 2195 Al-Li alloy sheets were investigated under a strain rate of 0.01, 0.1, 1 s and a temperature of 440 and 500 °C. Experimental results showed that the hot tensile properties of the 2195 Al-Li alloy sheet exhibited a strong dependence on loading directions. The peak stress (PS) and elongation (EL) along the rolling direction (RD) were larger than the transverse direction (TD). For the tests carried out at 440 °C-1 s, the PS values of the sheets stretched along the RD and TD are 142.9 MPa and 110.2 MPa, respectively. And, most of the PS anisotropy values are larger than 15%. The anisotropy in EL is less significant than in PS. All the differences are about 10%. Moreover, dimples in the samples stretched along RD were more and deeper than those along TD at 440 °C. The fracture morphology along RD and TD were similar, and both were cleavage fractures at 500 °C. Particularly, the fractions of high angle grain boundaries (HAGBs) along TD were all about 5% larger than those of RD. And, there were more small-sized continuous dynamic recrystallization (CDRX) grains inside the initial grains and discontinuous dynamic recrystallization (DDRX) grains featured with the local bulge of grain boundaries along TD. This was due to the smaller average Schmid factor and the vertical EL trend of the initial grains when the samples were stretched along TD. A model of grain evolution during the dynamic recrystallization (DRX) along RD and TD was proposed based on EBSD results. The Schmid factor and banded structure had a more prominent effect on the hot ductility of the 2195 Al-Li alloy compared with the degree of DRX, thus presenting a higher EL and better hot ductility along RD.
2195铝锂合金作为典型的第三代铝锂合金之一，在轻质航空航天结构中有着广泛的应用。本文研究了2195铝锂合金板材在应变速率为0.01、0.1、1 s⁻¹以及温度为440和500℃条件下的力学性能各向异性和微观组织演变。实验结果表明，2195铝锂合金板材的热拉伸性能对加载方向有强烈依赖性。沿轧制方向（RD）的峰值应力（PS）和伸长率（EL）大于横向（TD）。对于在440℃-1 s条件下进行的试验，沿RD和TD拉伸的板材PS值分别为142.9 MPa和110.2 MPa。并且，大多数PS各向异性值大于15%。EL的各向异性比PS的各向异性小。所有差异约为10%。此外，在440℃时，沿RD拉伸的样品中的韧窝比沿TD拉伸的样品中的韧窝更多更深。沿RD和TD的断口形貌相似，在500℃时均为解理断裂。特别地，沿TD的大角度晶界（HAGBs）比例均比沿RD的大角度晶界比例大5%左右。并且，沿TD方向，初始晶粒内部有更多小尺寸的连续动态再结晶（CDRX）晶粒以及以晶界局部凸起为特征的不连续动态再结晶（DDRX）晶粒产生。这是由于当样品沿TD拉伸时，初始晶粒的平均施密特因子较小且伸长率呈垂直趋势。基于电子背散射衍射（EBSD）结果，提出了沿RD和TD动态再结晶（DRX）过程中的晶粒演变模型。与DRX程度相比，施密特因子和带状组织对2195铝锂合金的热延展性影响更为显著，因此沿RD呈现出更高的EL和更好的热延展性。
