高强铝合金复杂曲面构件超低温成形增塑增强效应与微观演变机理

Cold forming or hot forming of high strength Al-alloy (Al-Cu-Mn/Al-Cu-Li) usually leads to inhomogeneous deformation, microstructure and properties, and induces macro or micro defects for the low plasticity at room temperature and poor hot work-hardening property of this material for complicated curved parts of new generation aerospace and aviation domains. A new method of cryogenic forming was proposed for complicated component of Al-alloy on the base of a new discovery on the enhancement effect of plasticity and strength of Al-alloy at low temperature. The complicated component of Al-alloy sheet is cooled down to low temperature by using cooling medium, and then deformed by using forming tools. The technique has the merits of improved forming limit, higher strengthen effect and non-microstructure damage. The scientific problems will be clarified on the enhancement mechanism of plasticity and strength under low temperature and complicated stress, as well as the microstructure evolution induced by complicated macro deformation. The main contents include: (1)The anisotropy mechanical properties and strain-hardening behavior of Al-alloy under very low temperature. (2)The forming limit and plasticity increasing mechanism of Al-alloy sheet under low temperature and complicated stress state. (3)The microstructure evolution and strain-hardening law after complicated plastic deformation. (4)The cryogenic forming process for complicated curved part and the controlling method for microstructure and mechanical performance. The fundamental theory on the new process of cryogenic forming for Al-alloy will be built in this study, and the new technology on controlling of precision and property for complicated part with high strength Al-alloy will be developed for aerospace and aviation.

新一代航空航天高强铝合金(Al-Cu-Mn/Al-Cu-Li)存在室温塑性低，热加工硬化性能差，导致复杂曲面件变形—组织—性能不均和热成形/热处理容易诱发宏观、微观缺陷的技术难题。为此，本项目在发现超低温下铝合金增塑增强效应基础上，提出铝合金复杂曲面构件超低温成形新方法，原理是通过冷却介质把铝合金板材冷却到超低温度，再利用模具成形出复杂曲面件，具有成形极限高、强化效果好和无组织损伤等优点。本项目旨在阐明超低温和复杂应力下铝合金增塑增强效应机理，以及复杂宏观变形诱发微观演变机制的科学问题。重点研究：超低温环境下铝合金各向异性力学性能和应变硬化规律；超低温和复杂应力状态下铝合金板成形极限和增塑机理；超低温下铝合金宏观变形诱发微观演变规律与强化机制；复杂曲面构件超低温成形工艺和组织性能控制。本项目为发展铝合金超低温成形新工艺奠定理论基础，为航空航天高强铝合金复杂曲面构件的成形和控性提供技术支撑。

针对铝合金薄板室温冷成形性能低，热成形易引发组织性能弱化和表面缺陷等难题，本项目发现了铝合金超低温变形“双增效应”，揭示了2219超低温下铝合金延伸率和硬化指数同时提高的宏微观变形机理；研制了超低温复杂应力下板材成形性能原位测试装置，揭示了2219铝合金薄板双向应力下的超低温变形行为，利用超低温DIC测试装置研究了2219铝合金板材复杂应力下的超低温拉深性能，获得了2219铝合金板材的超低温成形极限；提出了铝合金薄壁曲面构件超低温拉深成形新方法，开展了2219铝合金椭球曲面件的超低温拉深成形实验，建立了2219铝合金薄板超低温拉深成形工艺窗口，成形出厚径比3.1‰的2219铝合金半椭球曲面件，人工时效后，平均抗拉强度和延伸率分别为436MPa和6.1%。阐明了铝合金薄板超低温拉深成形过程缺陷形成机理，为铝合金薄壁曲面件超低温成形提供理论指导，为发展大尺寸铝合金薄壁构件超低温成形新工艺奠定理论基础。