2219铝合金多尺度微结构演变与过渡环高性能制造方法研究

The 2219 aluminum alloy belongs to the family of heat-treatable Al-Cu alloys, and is a structural material for transition rings in rocket tank. In this material, the concentration of Cu exceeds its solid solubility limit in Al matrix. Multi-scale microstructures existing in the material, such as micro-scale Al2Cu residual phase and nano-scale Al2Cu strengthening phase, have a major effect on the material’s mechanical properties. As the size of the ring increases, Cu segregation and the enrichment of the residual phase becomes more significant. The brittle residual phase can form crack sources and fast channels for crack propagation, which results in degradation in the material’s elongation rate and inhomogeneity over three directions. It has become one of the bottlenecks in the manufacture process of transition rings..In this project, a new idea is proposed to control the residual phase via a novel combination of deep cryogenic deformation and heat treatment. The residual phase is fully crushed under the strong shearing force during deep cryogenic deformation, whose dynamic recovery is restrained under low temperature. This environment favors the formation of a large number of fast diffused dislocation channels for solute atoms. Heat treatment is then performed to dissolve, diffuse and precipitate the residual phase, leading to a higher overall performance. This project focuses on the crush, dissolution and precipitation of the residual phase during deep cryogenic deformation and heat treatment. The effects of multi-scale microstructure evolution in 2219 aluminum alloy are investigated, which leads to a new method for high-performance manufacture of transition rings in rocket tank.

2219铝合金属于Al-Cu系可热处理强化合金，是火箭贮箱过渡环结构材料。该材料铜含量超过了其在铝基体中的极限固溶度，过渡环存在的多尺度微结构如微米级Al2Cu剩余相与纳米级Al2Cu强化相对环件力学性能有重要影响。随着运载火箭贮箱过渡环尺寸增大，铜偏析与剩余相富集现象更突出，脆性剩余相极易形成裂纹源与裂纹快速扩展通道，导致过渡环延伸率低、三向性能不均，已成为过渡环制造亟待解决的瓶颈问题之一。.本项目提出一种深冷变形与热处理协同调控过渡环剩余相的新思路，通过深冷变形强剪切力充分破碎剩余相，并在低温条件下抑制动态回复，有助于形成丰富的溶质原子快速扩散位错通道，随后经过热处理促进剩余相的溶解、扩散与弥散析出，以获得高综合性能。本项目重点研究深冷变形与热处理过程剩余相破碎、溶解与析出机制，探明2219铝合金材料多尺度微结构演变规律，形成2219铝合金过渡环高性能制造新方法。

运载火箭是我国深空探测、空间站建设、探月工程等领域的重要运载工具，2219铝合金过渡环是运载火箭贮箱结构的主承力构件，也是变形协调的核心部件，其整体力学性能及三向力学性能均匀性的指标要求不断提高。然而，2219合金中的铜含量超过了其在铝基体中的极限固溶度，采用传统成形工艺制造的构件存在大量团聚剩余相，成为裂纹源与裂纹扩展的快速通道，且晶粒组织极易发生长大、纤维化，导致构件力学性能偏低，各向异性突出，成为过渡环制造亟待解决的问题。.针对上述制造难题，本项目提出了环形件深冷成形新思路，利用合金在低温条件下强流变特性，充分打碎合金中的粗大组织，结合后续热处理，实现了残余结晶相弥散化、晶粒细小等轴化，提升了构件三向性能。具体研究成果如下：1）开展了2219铝合金深冷压缩试验，获得了合金深冷流变特性，发现铝合金在深冷条件下加工硬化能力与率大幅提升，且具备优异的塑性变形能力；2）研究了粗大残余结晶相在深冷变形与热处理过程中演变规律，发现在深冷多向锻造变形条件下，合金中的残余结晶相被充分破碎，结合高温固溶促进了溶解，大幅降低了残余结晶相比例；3）研究了深冷变形-热处理对2219合金晶粒组态的影响规律，发现随着变形温度降低与变形量增大，变形过程中存储能不断累积，促进了固溶过程中静态再结晶，形成细小等轴晶粒，在此基础上，建立了在2219合金不同变形条件下静态再结晶晶粒尺寸预测模型；4）开展了2219铝合金环件深冷成形物理模拟实验，相较于传统高温成形工艺，新工艺残余结晶相比例从1.55%下降至0.43%，晶粒尺寸从150μm降低至50μm，合金抗拉强度、屈服强度、延伸率分别从445MPa，343MPa，9.8%提高至484MPa，351MPa，13.2%。各向异性IPF指数从32.1%下降至7.8%。5）基于低温变形细化铝合金微结构思路，开发了2219铝合金环件轧制新工艺，实现了长征运载火箭Φ5米级过渡环高性能制造。上述研究成果为空天高性能构件成形制造提供了一种新的重要途径和理论支撑。