基于负压辅助气流的镀锌钢板零间隙激光搭接焊机理与方法

During the laser welding process of zinc-coated steel sheets with gap-free lap joint, some serious defects, such as blow holes, porosities and spatters, are as a result of that a mass of zinc vapor with high temperature and high pressure has not escaped from the interface between two sheets due to the boiling point of zinc (907℃) being far lower than steel melting point (1530℃). How to make the internal zinc vapor vent out smoothly is the key to solve this problem. So, this project is trying to use keyhole as venting channel for zinc vapor, thus inhibit defects and ensure welding quality, by taking a side suction or high speed gas flow along the horizontal direction to realize a local negative pressure above the keyhole and controlling the morphology and stability of the keyhole. Prominent features of this project is that we have firstly proposed a method that based on the assistant gas, which make the local negative pressure above the keyhole, to achieve a venting channel for the zinc vapor and a sound weld. Compared with existing methods, this method is more simple and easy to practice. Once its related mechanism and key technology are got breakthrough, it will provide automotive industry a laser overlap welding technology for galvanized steel sheets with no other additional process, low cost and easy to practice. What is more, this research can provide the guidance on solving the porosity problem for the laser penetration welding, which puzzled people in the industry and scholars for a long time.

镀锌钢板零间隙激光搭接焊过程中，由于锌的沸点(907℃)远低于钢的熔点(1530℃)，导致搭接面产生大量高温高压锌蒸气，这些锌蒸气如不能顺畅逸出则造成孔洞、气孔和飞溅等严重焊接缺陷。如何让内部锌蒸气顺畅逸出成为解决镀锌钢板激光焊接质量问题的关键。本项目拟直接利用小孔作为锌蒸气的逸出通道，采用侧吸或高速横吹辅助气流获得小孔上方的局部负压，以实现对小孔形态与稳定性的调控以利于锌蒸气的逸出，从而获得无缺陷的焊接接头。项目的突出特色在于：首次提出用负压辅助气流以实现锌蒸气自小孔逸出并获得完好焊缝的方法。与现有的众多方法相比，该方法更为简单实用，其相关机理与关键技术一旦获得突破，将会给汽车制造业提供一种无需任何其它附加工序、工艺简单且成本低廉的镀锌钢板激光搭接焊技术，且对解决长期困扰业界的激光焊接工艺气孔问题具有一定理论指导意义。

项目针对镀锌钢板激光搭接焊锌蒸汽引发的质量问题，提出负压调控小孔促使锌蒸汽逸出的新方法，从作用机理、焊接工艺及性能等方面阐述并验证该方法对锌蒸汽顺畅逸出的作用，并就该方法搭建完整的焊接实施装置。借助数值模拟手段，阐明了负压对小孔的调控作用和促进锌蒸汽逸出的作用机理；研究不同负压产生方式下各工艺参数的影响规律，获得形貌性能皆优的搭接接头并建立起完整的工艺窗口。通过本项目的研究，揭示锌蒸气以激光深熔焊的小孔为通道稳定有效逸出的物理机制，通过负压辅助气流的新方法实现对小孔形态及其稳定性的控制，实现镀锌钢板零间隙激光搭接焊中锌蒸气的有效逸出并阐明负压的作用机理，为实现镀锌钢板一类的低沸点镀层板（如有机镀层板）质量可靠、工艺简单的激光焊接提供理论和技术基础。同时，针对镀锌钢板-铝合金异种材料零间隙搭接焊进行拓展研究，实现了镀锌钢板-铝合金异种金属高强度连接。