热处理对2198铝锂合金板材各向异性力学行为的影响

Influence of Heat Treatment on the Anisotropic Mechanical Behavior of 2198 Al-Li Alloy Sheet

应用铝锂合金板材生产蒙皮等大型薄壁结构零件是航空制造轻量化的重要途径,本研究利用单向拉伸系统测试了不同热处理状态下2198铝锂合金板材沿着轧向(RD)、45°和横向(TD)方向的力学行为,研究了热处理对其各向异性的影响,并从晶体学织构、时效相和断口形貌分析了微观机制。结果表明,新淬火和自然时效状态的2198铝锂合金板材具有相似的各向异性,RD方向具有最高的强度、最高的硬化率和最低的延伸率,45°方向则具有最低的强度、最低的硬化率和最高的延伸率,主要原因是轧制板材存在强烈的<112>{110}织构。但是,经人工时效后的2198铝锂合金板材的各向异性因不均匀析出的T1相而发生了明显的变化,45°方向上的强度得到了较大程度的提升,具有和TD方向相同的水平,硬化率发生了明显的降低,TD方向成为硬化率最大的方向,而延伸率和断口形状的各向异性并未变化,可见T1相导致2198铝锂合金板材发生了各向异性的强化,却对断裂行为的各向异性影响较小。

The application of Al-Li alloy sheet with high specific strength and low fatigue crack growth rate for large thin-walled structural parts such as skin is an important way to reduce the weight of aeroplane. The mechanical behaviors of 2198 Al-Li alloy sheet along the rolling direction(RD), 45° and transverse direction(TD) were tested using unidirectional tension. The effect of heat treatment on its anisotropy was studied. The crystallographic texture, aging precipitate and fracture morphology were analyzed for the micro mechanism. It was found that the new-quenched and naturally aged 2198 Al-Li alloy sheet has similar anisotropy. The alloy along RD has the highest strength, the highest hardening rate and the lowest elongation. The alloy along 45° direction has the lowest strength, the lowest hardening rate and the highest elongation. The main reason is the strong <112>{110} texture in the rolled sheet. However, the anisotropy of the 2198 Al-Li alloy sheet after artificial aging has changed significantly due to the inhomogeneous precipitation of the T1 phase. The strength in 45° direction has been greatly improved to the level as same as that along TD. And the hardening rate is significantly reduced. TD becomes the direction with the largest hardening rate. The anisotropy of elongation and fracture shape does not change. It can be seen that the T1 phase causes the anisotropic strengthening of the 2198 Al-Li alloy sheet but it has little effect on the anisotropy of fracture behavior.