Abstract Creep age forming (CAF), under thermal-mechanical environment, may be sensitive to the thermal and mechanical loading conditions. Unfortunately, the different creep aging (CA) behaviors under two inverse thermal-mechanical loading sequences, viz. loading-heating (LH) and heating-loading (HL), are almost neglected in experiments or modeling of CAF. In this work, taking solution treated 5A90 Al-Li alloy as a case material, the loading sequence related CA behaviors of the alloy are investigated using continuous/interrupted tensile CA tests at 130 °C/175 MPa combined with high-resolution Transmission Electron Microscope (HRTEM) and mechanical properties tests. The results show that, the inverse loading sequences result in different initial tempers for CA process, viz. solution temper under LH and stress-free aged temper under HL. The solution temper for CA process under LH can lead to a more stable and repeatable CA process than HL does, which causes a stress-free aged temper with randomly and discretely distributed precipitates for CA process. After two inverse loadings and 18 h of isothermal CA, the total creep deformation for LH (0.1475%) is twice larger than that for HL (0.0720%), thanks to the remarkable creep strain in the LH non-isothermal CA process with 49.2% of total creep strain. The samples under LH present a lower strength and a higher elongation than those under HL during the whole process, and the gap of the mechanical properties of samples under the two loading sequences reaches its maximum (15 MPa for yield strength and 8.45% for elongation) after 0.5 h of isothermal CA, and then gradually decreases in subsequent process. After 0.5 h of isothermal CA, though the volume fraction of the δ′ precipitates (Al3Li) under LH is larger than that under HL, the dislocations density under LH is less than that under HL, which makes a lower material strength under LH. It is noted that, after 18 h of isothermal CA, the microstructures and macroscopic mechanical properties of the samples have less disparity for the two inverse loading sequences.

中文翻译：

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热机械加载顺序对5A90铝锂合金蠕变时效行为的影响

摘要 蠕变时效形成 (CAF) 在热机械环境下可能对热和机械载荷条件敏感。不幸的是，在两个逆热机械加载序列下不同的蠕变老化 (CA) 行为，即。加载-加热 (LH) 和加热-加载 (HL) 在 CAF 的实验或建模中几乎被忽略。在这项工作中，以固溶处理的 5A90 Al-Li 合金为外壳材料，使用 130 °C/175 MPa 的连续/间断拉伸 CA 测试结合高分辨率透射电子显微镜研究了合金的加载顺序相关的 CA 行为(HRTEM) 和机械性能测试。结果表明，反向加载顺序导致 CA 过程的不同初始状态，即。LH 下的固溶回火和 HL 下的无应力时效回火。LH 下 CA 工艺的固溶回火可以导致比 HL 更稳定和可重复的 CA 工艺，这导致 CA 工艺中出现随机且离散分布的析出物的无应力时效回火。在两次反向加载和 18 小时等温 CA 后，LH 的总蠕变变形 (0.1475%) 是 HL (0.0720%) 的两倍，这要归功于 LH 非等温 CA 过程中显着的蠕变应变为 49.2%总蠕变应变。在整个过程中，LH 下的样品比 HL 下的样品呈现出较低的强度和较高的伸长率，两种加载顺序下样品的力学性能差距达到最大（屈服强度为 15 MPa，伸长率为 8.45%）等温 CA 0.5 h 后，然后在后续过程中逐渐降低。等温 CA 0.5 小时后，尽管LH下δ'析出物（Al3Li）的体积分数大于HL下的，但LH下的位错密度小于HL下的位错密度，这使得LH下的材料强度较低。值得注意的是，在等温 CA 18 小时后，样品的微观结构和宏观力学性能对于两种反向加载序列的差异较小。