2219铝合金运载火箭贮箱过渡环粗大结晶相消减方法与机理研究

2219 aluminum alloy has excellent comprehensive mechanical properties and is the preferred structural material for the transition ring of the launch vehicle tank. The content of Cu in this material is high, resulting in easy formation of coarse Al2Cu constituent phases during casting process. As the size of the transition ring increases, the phenomenon of Cu segregation and constituent phases enrichment in large ignot is more prominent, which is easily inherited to the final ring, and becomes a stress concentration and crack initiation source, resulting in poor mechanical properties of the ring. It has become one of the bottlenecks in manufacturing of the large transition rings.. In this project, an new process is proposed to reduce the coarse constituent phases of the transition rings via combination of high temperature–low temperature alternating deformation and heat treatment. The high-temperature (close to the solution treatment temperature) deformation is used to dissolve the coarse constituent phases fully and improve the matrix plasticity; the low-temperature deformation is used to fragment the coarse constituent phases, thus increasing the surface energy of the constituent phases and the dislocation density in the matrix, which promotes the dissolution of the constituent phases and precipitation of the strengthening phases in the subsequent heat treatment, and improves the mechanical properties of the material. This work focuses on studying the basic scientific issues such as the evolution rules and refinement mechanism of coarse constituent phases under different thermo-mechanical coupling conditions，the mechanism and effect of constituent phases on mechanical properties of 2219 aluminum alloy, obtaining the method and mechanism of reduction of coarse constituent phases and improvement of mechanical properties, and thus provides a theoretical reference for manufacuting large and high-performance transition rings.

2219铝合金具有优异的综合力学性能，是运载火箭贮箱过渡环的首选结构材料。该材料中的Cu元素含量高，铸造过程中极易形成粗大Al2Cu结晶相；随着贮箱过渡环尺寸的增大，大铸锭带来的铜偏析与结晶相富集现象更为突出，并遗传至最终环件，成为应力集中和裂纹萌生源，导致环件力学性能偏低，这已成为大型过渡环制造亟待解决的瓶颈问题之一。.本项目提出一种高低温交替变形与热处理协同消减过渡环粗大结晶相的新思路，利用近固溶温度高温变形充分溶解粗大结晶相，改善基体的塑性；通过低温变形破碎粗大结晶相，增大结晶相粒子的表面能和基体位错密度，促进结晶相在随后热处理过程中的溶解及时效析出，提高材料的力学性能。重点研究不同热力耦合条件下粗大结晶相的演变规律与细化机制、结晶相对2219铝合金力学性能的影响及作用机理等基础科学问题，获得过渡环粗大结晶相消减与性能提升的方法及机理，为大型过渡环高性能制造提供方法与理论指导。

运载火箭是目前人类进入太空的唯一运输工具，其运载能力体现了国家综合国力、太空竞争实力和科技创新水平。过渡环是运载火箭贮箱的重要组成部分和主承力构件，被称为运载火箭的“脊梁”和“制造基准”，通过不断提升其轻质化指标、以提升火箭运载能力是火箭结构发展的重要方向。.为实现探月工程、空间站建设等重大航天工程，我国研制了长征五号运载火箭，火箭箭体直径及过渡环件直径均达到Ø5m，此前我国无该超大规格环件整体成形制造先例，前期按常规方法试制极易出现延伸率不达标、各向异性突出，严重制约了型号研制目标的实现。.贮箱过渡环选用综合力学性能和焊接性能优异的2219铝合金，该材料中的Cu元素含量高，铸造过程中极易形成粗大Al2Cu结晶相；随着贮箱过渡环尺寸的增大，大铸锭带来的铜偏析与结晶相富集现象更为突出，并遗传至最终环件，成为应力集中和裂纹萌生源，是导致环件性能不达标的关键因素。.本项目针对大型贮箱过渡环存在粗大结晶相富集导致力学性能不达标难题，提出高低温交替变形与热处理协同消减粗大Al2Cu结晶相粒子的新思路。重点研究了不同温度下Al2Cu结晶相的细化机制，高低温交替变形复杂能场条件下Al2Cu结晶相的演变规律及机理，高低温交替变形与热处理协同下过渡环结晶相消减方法与性能提升原理等科学问题，获得的主要结果如下：.（1）获得了粗大结晶相和铝基体物理特性及其适宜的变形工艺区间，探明了高温、低温变形工艺对2219铝合金粗大结晶相细化的影响规律，揭示了不同变形温度下粗大结晶相的细化机制。.（2）揭示了高温多向锻造大流变、中低温强变形、热处理工艺对结晶相粒子细化的影响及机理，提出了“高温大流变+中温强流变+高温固溶”协同消减粗大结晶相的新方法，减少、细化、球化了粗大结晶相。.（3）获得了高低温交替变形与热处理作用下粗大结晶相粒子在环件制造全流程中的遗传和演变规律，揭示了粗大结晶相对力学性能的影响机制，提出了多重“中温环轧+高温固溶”环件制造新工艺。.（4）采用新工艺研制成功长征五号运载火箭Ø5米整体贮箱过渡环，减少了环件中的粗大结晶相，环件强度与延伸率显著提升，三向力学性能均满足指标新要求，为运载火箭结构减重和可靠性提升提供了重要支撑。.（5）发表了SCI学术论文5篇（另有1篇机械工程学报已录用，1篇SCI返修），作学术报告2次，申请发明专利1项，协助培养研究生2名。