7xxx系铝合金多级复合能场蠕变时效成形组织性能定量调控

Creep age forming technology carries out creep deformation and aging strengthening simultaneously, providing an important way to realize the integrated coordination of precision shape forming and properties tailoring of high-strength aluminum alloy integral panel components. The potentials of creep deformation and aging strengthening of the material can be more fully released by applying assisted electric field and appropriate multistage aging system on the basis of the original thermal-mechanical field. However, the dynamic interaction between creep and aging under the multistage composite energy field will be more complex, leading to the precise control of the microstructures and properties of material more difficult. To this end, the quantitative control of microstructures and properties of high-strength aluminum alloy in creep aging process under multistage composite energy field is the key scientific problem urgently to be solved. In this study, the creep aging behaviors of 7xxx series aluminum alloys under multistage composite energy field will be studied to reveal the quantitative influence rule of multistage composite energy field on microstructures evolution, investigate the quantitative correlation between microstructures and material properties, determine the processing scheme and parameter control range of creep age forming under multistage composite energy field, and thus the quantitative control method of microstructures and properties of 7xxx series aluminum alloys in creep age forming under multistage composite energy field will be obtained. This research is critical to developing the theory and technique of creep age forming, and will provide a basis for improving the manufacturing level of high-strength aluminum alloy integral panel components.

蠕变时效成形技术将蠕变变形和时效强化同步进行，为实现高强铝合金整体壁板类构件的精确成形成性一体化制造提供了重要途径。在原有热-力场的基础上施加电场辅助并采用合理的多级时效制度可更加充分地发挥材料的蠕变变形和时效强化潜能。然而，多级复合能场下的蠕变和时效动态交互作用将更加复杂，材料组织性能的精确控制更为困难。因此，如何实现高强铝合金多级复合能场下蠕变时效过程中组织性能的定量调控成为迫切需要解决的关键科学问题。本项目研究7xxx系铝合金在多级复合能场下的蠕变时效行为，揭示多级复合能场对微观组织演变的定量影响规律，探明微观组织与材料性能的定量关系，确定多级复合能场蠕变时效成形工艺方案及参数调控范围，获得7xxx系铝合金多级复合能场蠕变时效成形组织性能定量调控方法。本研究对发展蠕变时效成形理论和先进技术具有重要意义，可为提升航空航天领域高强铝合金整体壁板类构件高性能成形制造水平提供依据。

蠕变时效成形技术将蠕变变形和时效强化同步进行，为实现高强铝合金整体壁板类构件的精确成形成性一体化制造提供了重要途径。在原有热-力场的基础上施加电场辅助并采用合理的多级时效制度可更加充分地发挥材料的蠕变变形和时效强化潜能。针对7xxx系铝合金多级复合能场蠕变时效成形组织性能定量调控，本项目综合采用理论分析、试验表征和数值模拟相结合的方式进行了系统的研究，取得的主要研究进展如下。（1）研究了多级复合能场蠕变时效过程中蠕变变形行为。为排除焦耳热效应对蠕变时效成形的影响，建立了7050铝合金在给定条件下焦耳热效应与电脉冲参数之间关系的经验公式，获得了焦耳热效应可控的电脉冲参数组合。对比了热-力加载和保载阶段施加电脉冲对蠕变变形量的促进作用，发现在热-力加载阶段即蠕变初始阶段效果显著，而在热-力保载阶段即蠕变稳态阶段效果微弱。变形量增大的原因是电脉冲降低了弹性模量并促进了位错运动。（2）探明了多级复合能场对蠕变时效过程中组织性能演变影响规律。对比了单级峰时效、双级过时效、传统回归再时效、电致回归再时效制度蠕变时效过程中的微观组织和性能演变，发现电脉冲可以促进溶质扩散、析出相形核和位错运动，合金在采用电致回归再时效制度的蠕变时效过程中可以获得理想的晶内和晶界沉淀相微观组织以及较高的力学性能和耐蚀性能。（3）揭示了多级复合能场蠕变时效过程中组织性能的定量关系。引入电脉冲参数，建立了热-力-电场作用下的蠕变时效微观组织演变模型。根据不同微观组织特征参量与其各自决定的强化机制之间的关系，建立了综合考虑时效强化、固溶强化和位错强化的力学性能变化模型。（4）获得了多级复合能场蠕变时效成形工艺方案和参数调控范围。以组织性能特征参数为内变量，结合微观组织定量表征，建立了蠕变时效本构模型。分别进行采用一次电脉冲、两次电脉冲、传统回归再时效和电致回归再时效制度的蠕变时效成形数值模拟和试验研究，以成形件的目标组织性能和回弹量为评价依据，获得了最优的多级复合能场蠕变时效成形工艺为电脉冲辅助热-力加载峰时效蠕变时效成形加电致回归处理再蠕变时效成形。