铝锂合金板材高速冲击液压成形特性及宏微观变形机理

Aluminum-Lithium (Al-Li) alloys have gained great attention for military, aircrafts, space, and commercial application because of their outstanding properties, such as high specific stiffness, high specific strength, high elastic modulus and low density. However, their poor fracture toughness and low formability particularly at room temperature cannot fulfil the requirements of manufacturers and designers for modern aircrafts and space applications. Furthermore, anisotropic mechanical properties which is considered as the major issue of Al-Li alloys, lead to serious problems in product manufacturing and quality.. In this project, the novel high speed impact hydroforming technology will be developed to form complex structural components with precise details from Al-Li alloys sheets at room temperature. The project aims at investigating the deformation mechanisms and formability of Al-Li alloy sheets under the impact hydroforming technology by the advanced simulation algorithms for multi-scale coupling and multi fields coupling of solid-liquid-force. It is divided into four major stages as follows: firstly, the characteristics of solid-liquid impact loading will be analyzed; secondly, the deformation mechanism leading to improve mechanical properties and formability of Al-Li alloys under impact hydroforming will be investigated through quasi-static – dynamic tensile tests and microstructure evaluation; thirdly constitutive model and forming limit diagram model will be developed to predict flow curve and formability of AL-Li alloys respectively under dynamic loading; finally, based on the results obtained from previous stages, the process parameters will be optimized and a process window will be created to form kinds of complex structural components. . This project offers a theoretical understanding of the keys leading to accurate control and quantitative design of impact hydroforming process for Al-Li alloys sheets combined with the both characteristics of material and parts. It provides the leading technology with high efficiency, short process and green intelligence for the potential application on complex structural components of novel Al-Li alloys in the aircrafts and space industries.

铝锂合金具有密度低、弹性模量高、比强度和比刚度高等优异的综合性能，但是其室温塑性差、各向异性明显、冷加工易开裂，严重制约其在航空航天领域的应用。为此，本项目创新性地采用高速冲击液压成形新技术实现铝锂合金复杂薄壁构件的室温精确成形，将高应变率和柔性有机结合以提高材料成形能力和零件成形质量。围绕固-液冲击传载的物理特性和铝锂合金板材的动态响应规律、固-液冲击载荷与铝锂合金微观组态演化及断裂行为之间的交互作用机制、冲击体和液室的物理参量与铝锂合金板材成形性之间的定量关系等科学问题，系统研究固-液-力多场耦合作用下铝锂合金板材的动态变形行为和成形特性，揭示铝锂合金板材塑性变形能力提高的微观机理、建立高应变率下板材成形极限的精确预测模型，实现铝锂合金板材高速冲击液压成形工艺的精确调控和定量设计，为新型铝锂合金在航空航天高性能复杂构件中的应用提供国际领先的高效率、短流程、绿色智能制造的前瞻性技术支持。

本项目创新性地采用高速冲击液压成形新技术实现铝锂合金复杂薄壁构件的室温精确成形，将高应变率和柔性有机结合以提高材料成形能力和零件成形质量。围绕固-液冲击传载的物理特性和铝锂合金板材的动态响应规律、铝锂合金板材的动态力学行为和成形特性、铝锂合金变形中的微观组织演变和变形机理、铝锂合金复杂薄壁构件的冲击液压成形工艺优化和实验验证等科学问题，开展了系统的研究。获得主要结果如下：（1）自主设计研制了“固-液-固”冲击传载时空特性的检测装置，发现了冲击波对材料的二次加载作用。且单冲击体形式下的能量利用率更高；（2）发现了铝锂合金高应变速率增塑效应，当应变速率从0.01/s增加到4200/s时，AA2195的延伸率由22%增加到63%，抗拉强度由334MPa增加到398MPa。建立了修正的JC本构模型，对不同应变速率下AA2195的硬化行为预测误差可控制在6%以内；（3）阐明了材料在冲击液压成形下的变形特性，所具有的惯性效应会改变成形时的流动时序。对于对称结构，材料倾向于从两端向中心区流动，对于非对称结构，材料流动方向则正好相反；（4）揭示了AA2195高应变速率下延伸率提升的微观机理，即高应变速率拉伸下软取向晶粒的塑性变形更加充分，而且更多的硬取向晶粒参与协调变形；（5）构建了固-液耦合有限元模型，结合冲击液压成形实验，获得了冲击能量-拉深比曲线和拉深深度比-拉深比变化曲线，提出了冲击液压成形性能评测新方法；（6）开展了航空典型锥形罩类和半管类零件的冲击液压成形定量化工艺设计，实现了成形冲孔一体化制造，零件最大减薄率低于25%，冲孔塌角高占比低于20%。此外，还针对AA2195的热处理强化制度进行了探索性研究，结果表明在190℃×4h+160℃×32h双级时效下，抗拉强度达588MPa，延伸率为13.5%。并且双级时效下长宽比大的T1相是合金强度提高的重要因素。本项目的研究结果将为新型铝锂合金在航空航天高性能复杂构件中的应用提供国际领先的高效率、短流程、绿色智能制造的前瞻性技术支持。