双金属管磁脉冲复合协调变形机制及界面塑性流动行为研究

Bi-metal tube combines the preponderant properties of two different metals in one. Compared to a metal tube of single material, a bi-metal tube has the advantages of saving precious metals, reducing costs and expanding part's function, which result in the broad prospect of application of bi-metal tube in modern industry. The bi-metal tubes have been one of the important deveolopment trends of high-performance materials. This proposal brings forward a novel method for fabricating bi-metal tubes, named an incremental magnetic pulse cladding. On the basis of preliminary exploratory studies, the project now focuses on the coordinate deformation between two sequential cladding steps and the dynamic plastic flow behavior of clad materials under pulsed magnetic forces, via the experiments, theoretical analysis, numerical simulation and advanced testing technologies. The mechanism of the coordinate deformation, the rule of the dynamic plastic flow on the interface during the cladding, and the rule of the dynamic diffusion of basic elements across the bonding interface are to be explored and disclosed. Then the cladding processing prameters are to be optimized on the guideline of the previous results and the deep investigation of the mechanical properties of cladding joints, the microstructure characteristics and their evolution during the increamental cladding process, will be performed to reveal the interrelationship among the process parameters, the microstructure characteristics of the cladding joints and the performance of bi-metal tubes. The results from the project could form the theory basis on how to control the properties of bi-metal tubes and lay the foundation for research and development of this new, green and cost saving technology for manufacturing of high performance bi-metal tubes.

由异种金属复合而成的双金属管可以综合利用两种金属的优势性能，相对于单一组元材料的金属管，具有节约贵重金属、降低成本、扩展功能等优势，在现代工业中有广泛的应用前景，已成为高性能材料发展的重要方向之一。本项目提出了制造双金属管磁脉冲复合新方法，在前期探索研究的基础上，拟通过试验、理论分析、数值模拟和分析测试手段，研究脉冲磁场力作用下复合步间协调变形行为和界面材料的塑性流动行为，揭示双金属管磁脉冲复合协调变形机制、复合界面塑性流动规律和基体元素动态扩散机制；在此基础上优化磁脉冲复合过程的工艺参数，深入研究复合界面力学性能、复合界面的微观结构特征及其在渐进式复合过程中的演变规律，进而揭示双金属管磁脉冲复合过程中工艺参数、界面特征与材料使用性能的关联性。课题研究结果将为双金属管复合性能调控奠定理论基础，为实现高性能双金属管的绿色、节能制造提供理论和技术支撑。

双金属复合管充分利用了基管和复管材料的优异性能，具有节约贵重金属、降低成本、扩展功能等优势。本项目针对双金属管材磁脉冲复合新技术的应用基础问题，对渐进脉冲电磁力作用下双金属管磁脉冲复合过程塑性变形行为进行了研究，发现复合管表面出现 “凸棱”缺陷是由于复管在渐进分区复合过程中过渡变形区与待变形区的变形不协调而引起，基于此进一步分析了脉冲磁场力的时空特性，提出了优化设计集磁器工作区结构的原则，实现了复管的协调变形控制。针对冲击接触界面材料大变形特征，采用光滑粒子流体动力学方法（SPH）建立了冲击界面的数值模拟模型，深入研究了复合界面塑性流动行为。结果表明，在磁脉冲复合过程中，单一的涡流热效应不足以引起复合界面材料发生熔化，涡流和冲击接触界面材料塑性变形的联合作用则可以使界面温度升高至Al母材的熔点。伴随着强烈塑性剪切变形的紊乱波形界面区是界面高温区，其温升可使复合界面Al侧母材熔化。研究了1060Al/20#钢磁脉冲复合界面微观组织结构特征，发现1060Al-20#钢磁脉冲复合界面存在无过渡区结合的扩散界面和带过渡区结合的熔合界面。扩散界面仅是一条宽度约10 nm、原子呈无序结构排列的边界层，其两侧为母材基体，Al 侧母材三角晶界非晶化。分子动力学（MD）模拟结果表明，扩散界面形成机制为Fe原子在无序化Al基体中的快速迁移。带过渡区的熔合界面由于过渡区熔化而后快速凝固而形成，过渡区包含了原子呈无序结构排列的基体相和弥散分布于其中的纳米晶，无序基体相中氧元素的含量可占到10 at.%。 探讨了复合界面组织形貌特征与界面力学性能的关联机制，对于界面相对结合强度（相对于Al母材的剪切强度）达到100%的1060Al/20#钢磁脉冲复合界面，其良好的结合性能与呈小波状的“直接”结合界面相关联。宽过渡区内包含的微孔洞、微裂纹等缺陷破坏了复合区的连续性与整体性，降低了复合界面的结合效果。本项目的成果丰富了异种金属高速冲击焊接理论，为双金属管的高性能制备提供了重要技术支撑。