不完全互溶金属激光熔钎焊熔池界面形态及连接机理研究

Laser welding-brazing, an advanced laser joining technology, is an acceptable way for joining dissimilar materials, and has great potential applications in industrial, aerospace, military and other fields. Both fusion and brazing occur during laser welding-brazing process with complex physical mechanisms. Liquid-liquid interface formed in the molten pool has a significant impact on weld morphology, mass diffusion, and mechanical properties. This study focuses on laser welding-brazing process for dissimilar materials with incomplete miscibility. An in-depth research on liquid-liquid interface evolution in molten pool and joining mechanism is carried out. The main contents are as follows. Influences of process parameters on the weld morphology are investigated by process experiments and theoretical analysis. Fluid dynamics model of for laser welding-brazing process is established, under considerations of surface tension, buoyancy and diffusion driven by chemical potential gradient. Based on the model, temperature field, flow field and element distribution is calculated to explore the relationship between the process parameters and evolution of molten pool. Stress state of the weld is analyzed by microtesting and numerical simulation, considering interface discontinuity.This study aims to reveal the mechanism of convective heat and mass transfer during laser welding-brazing process, establish a relationship among control parameters, evolution of molten pool and joint mechanical properties, and find the key control parameters affecting welding quality. It is meaningful to develop laser welding theory, optimize the laser welding-brazing process, and promote its applications for joining dissimilar materials in industrial field.

激光熔钎焊接是一种新兴的激光焊接工艺，是解决异种难焊材料连接的可行手段，具有巨大应用潜力。不完全互溶金属激光熔钎焊接同时包含熔焊与钎焊，物理效应复杂，在熔池中形成液-液界面，对焊缝形貌、质量扩散及力学性能产生重要影响。本项目以不完全互溶异种金属激光熔钎焊接过程为研究对象，对激光熔钎焊接熔池液-液界面演化及连接机制进行研究。具体内容包括：实验观察与理论分析熔池形貌多参数耦合作用机理；研究激光熔钎焊接熔池液-液界面演化，以及基于化学势梯度驱动的质量扩散；探索界面不连续对焊缝应力状态影响机制。本项目旨在揭示不完全互溶异种金属激光熔钎焊接熔池界面演化机制，建立"控制参数?熔池演化?力学性能"对应关系，提出影响焊接质量的关键工艺参数，从而实现工艺优化。项目成果将丰富激光焊接基础理论，拓展激光熔钎焊接工艺应用领域。

激光熔钎焊接是一种新兴的激光焊接工艺，是解决异种难焊材料连接的可行手段，具有巨大应用潜力。不完全互溶金属激光熔钎焊接同时包含熔焊与钎焊，物理效应复杂，在熔池中形成液-液界面，对焊缝形貌、质量扩散及力学性能产生重要影响。本项目以钛合金Ti6Al4V与铅（Pb）激光熔钎焊接过程为研究对象，对激光熔钎焊接熔池液-液界面演化及连接机制进行研究。具体内容包括：实验观察与理论分析熔池形貌多参数耦合作用机理；研究激光熔钎焊接熔池液-液界面演化，以及基于化学势梯度驱动的质量扩散；探索界面不连续对焊缝应力状态影响机制。通过项目研究发现，无量纲数△D/d（光斑偏移量/光斑直径）是影响焊接形貌的关键参数；对比Ti6Al4V 与Pb，Ti与Pb激光熔纤焊接过程，由于Ti与Pb元素的不完全互溶特点，Ti6Al4V与Pb焊接熔池中存在液-液界面，并通过三元化学势模型，分析了形成液-液界面的根本原因；对焊缝微区进行力学性能测试，并计算焊缝中热应力分布，不完全互溶异种金属激光焊接焊缝在液-液界面凝固后，形成材料属性不连续界面，是焊缝应力集中区域，直接影响焊缝力学性能。本项目旨在揭示不完全互溶异种金属激光熔钎焊接熔池界面演化机制，建立“控制参数↔熔池演化↔力学性能”对应关系，提出影响焊接质量的关键工艺参数，从而实现工艺优化。项目成果将丰富激光焊接基础理论，拓展激光熔钎焊接工艺应用领域。