光束扫描和微合金化复合增强铝合金激光-电弧复合焊接头微结构与凝固裂纹抑制机理

In the high-end manufacturing area, such as aerospace and high-speed trains, high-quality, high-efficiency laser-MIG hybrid welding of aluminum alloy in medium-thick structures is a great demand and research focus. However, the hybrid welds are high sensitivity to solidification cracks and the microstructure of weld is macro-segregation at high welding speed, which is hard to achieve sound weld joint. We put forward to a new idea named as oscillating laser beam-arc hybrid welding based on metal core wire with high frequency laser beam oscillator to overcome this question, which utilizes the combination of oscillating laser beam and microalloying elements to strengthen the microstructure and solidification crack resistance of aluminum alloy weld. This study aims to investigate the effects of the high frequency osicillating of laser beam on the arc characteristics, dorplet transfer and laser-arc interaction during hybrid welding, explores the effects of the combination of strong stirring induced by laser beam oscillating and microalloying elements on the complicated metallurgical behaviors, such as the heat and mass transfer of the molten pool, the migration and transition of microalloying elements, weld solidification and crystallization, etc., and subsquently discuss the relationships between the metallurgical behaviors and the joint mcirostrucutre and solidification crack formation. According to the research results, based on the composite strengthen effect of oscillating beam and microalloying, the controlling strategies for joint quality would be developed. The results obtained in this study can provide theoretical basis and technical support for high efficiency and high quality welding of aluminum alloy.

铝合金中厚板结构的高质量、高效率激光-MIG复合焊接是航空航天、高速列车等高端制造领域的重大需求和研究重点，但在较高焊接速度下其接头凝固裂纹敏感性高，焊缝组织不均匀，接头质量难以保证。本项目提出基于金属粉芯铝焊丝的振荡扫描激光-电弧复合焊接新方法，利用扫描激光束和可促进晶粒细化的微合金元素的复合作用，共同增强铝合金焊缝微观组织和凝固裂纹抗性。本项目将围绕其中的关键科学问题进行研究，揭示激光束高频振荡扫描的动态行为对电弧特性和激光-电弧相互作用的影响规律；探索在高频振荡扫描激光束驱动的熔池搅拌效应与微合金化元素的复合作用下，熔池传热传质、“微合金化”元素的迁移和过渡、焊缝凝固结晶等复杂冶金行为的变化规律，及其和微观组织与裂纹形成机制的内在关联。在此基础上，提出光束扫描和微合金化复合增强的铝合金激光-电弧复合焊接头性能调控方法，为铝合金的高效率、高质量焊接提供理论依据和技术支撑。

围绕基于金属粉芯药芯铝焊丝的振荡扫描激光-电弧复合焊接新方法的关键科学问题开展了系统研究，制备了专用铝合金药芯焊丝，获得了优化粉芯配方，显著提高了复合焊接效率，达到了晶粒细化、抑制裂纹的预期目标，获得了高强韧性焊接接头。主要研究结果如下：（1）获得了兼具高熔深和良好焊缝表面形貌的带有稳弧剂和形核剂的多组元优化活性剂配比，具体质量分数为13.485%的SiO2，13.485%的Cr2O3，53.78%的NiO，12.35%的碳酸钾，1.9%的碳酸钠，2.5%的钛铝合金以及2.5%的锆铝合金。基于此，制备了用于激光-电弧复合焊接的专用铝合金药芯焊丝。（2）基于药芯焊丝的复合焊接效率较常规实心焊丝复合焊接显著提升，同等熔深条件下所需焊接电流下降50.6%，焊接速度提升50%，激光功率下降14%。（3）激光束扫描行为可以增强激光光致等离子体-电弧等离子体的相互作用程度，降低电弧中心区的电阻率。尤其是圆形扫描具有最强的等离子体相互作用，主要表现在激光辐照区和电弧中心区的光谱强度比无扫描复合焊接分别提升了30%和33%；电子温度分别提升了9%和8.5%；而电子密度提升主要在电弧中心区，提升幅度为43%。圆形扫描具有最强的激光-电弧等离子体相互作用，在相同扫描参量条件下，圆形扫描的熔滴过渡时间最短且直径最小，比无扫描分别减小了 44%和 47%，表现为典型的细颗粒射滴过渡模式。（4）粉芯中的“微合金化”成分起到了孕育剂作用，结合激光振荡扫描搅拌熔池的特性，焊缝微观组织得到明显细化，焊缝中凝固裂纹显著减少，促进了焊缝强韧性显著提升。