二维超声振动-激光复合焊接特性及熔池行为研究

Laser beam welding is an advanced welding method to realize the joining the aluminum alloys. However, it is also challenged by the welding instability, porosity, cracks and poor appearance of weld. To overcome these problems, a novel joining technique named as two-dimensional ultrasonic-laser hybrid welding is proposed. The laser head is excited by two perpendicular ultrasonic vibration with the same frequency. Based on the principle of vibration synthesis, the laser beam will move in oval or circular or linear trajectory. Meanwhile, the ultrasound is introduced into the weld pool by the laser beam. By the synergic effect of the oscillating laser beam and the ultrasound, not only the weld porosity could be avoided but also the joint mechanical properties could be improved significantly. This study aims to explore the synergic effect on the metallurgical behaviours in molten pool including heat and mass transfer, alloying elements migration, weld metal crystallization and defects formation, and subsequently discuss the relationships between the metallurgical and joint properties. An acoustic-fluid coupling model is established to explore the effect of cavitation and acoustic streaming on the microstructural evolution of the weld pool. A laser energy deposition model is also established to better understand the influence of ultrasound on the distribution of laser energy field. The inherent characteristics among the composite field, weld pool behavior and weld formation will be revealed by the study. The results obtained in the study shall be a good reference for high quality welding of aluminium alloys, and also useful to enrich the fundamental theory of ultrasonic-laser hybrid welding.

针对铝合金激光焊接稳定性差、易产生气孔及裂纹的特点，本项目提出一种二维超声振动-激光复合焊接铝合金的新方法、新工艺：基于振动合成原理，对激光头施加两个相互垂直同频超声激励,使光束沿椭圆形/圆形/直线形轨迹进行运动，同时超声以光束为载体导入熔池，实现既消除焊缝气孔又改善焊缝组织、提高焊接接头性能的目的。通过研究超声-激光复合作用对熔池传热传质、合金元素烧损迁移、气孔缺陷演变、焊缝结晶凝固等熔池冶金行为的影响规律，探析焊缝的强韧机制；建立适用于超声-激光复合焊接的声-流耦合模型，探索超声产生的空化效应、声流效应对熔池凝固过程能量传递与组织形成的作用机理；构建激光能量在材料表面沉积模型，研究超声对激光能场分布的影响规律，揭示复合能场特征—熔池行为—焊缝成形的内在关联，为铝合金的高质量焊接提供理论依据和技术支撑，并丰富超声-激光复合焊接基础理论。

为了拓展激光焊接的应用，本项目提出一种二维振动辅助激光的复合焊接新思路。基于高频逆变技术与嵌入式系统，提出了一种双路逆变结构的主电路拓扑，并采用TMS32F409处理器作为控制核心，研制了双路信号输出电源系统，实现了两路激励信号相位差的精确控制。采用柔顺铰链结构，研制了一套解耦非共振型二维振动合成机构，实现了二维振动的有效合成，实现了二维振动系统与激光头的有效耦合。基于复合焊接系统开展了工艺试验，研究分析了振动幅值及频率对高强钢焊缝组织特征和接头力学性能的影响规律，结果表明通过增大振幅和频率可以促进光束的搅拌效应，进而有效细化焊缝晶粒，避免元素的偏析，通过工艺参数优化在深熔焊熔透模式下可以获得无缺陷的焊接接头，焊缝强度可以达到母材的强度。构建了光束在材料表面的运动模型，采用Matlab计算获得了不同轨迹模式下光束在材料表面的能场分布特征，结果表明焊接速度、振幅和频率是影响能场分布的关键，圆形振动模式能场分布一致性好，获得的焊接质量高；在焊接速度和振幅不变时，频率超过一定范围对能场分布影响较小。