铝合金横焊柔性变极性等离子弧的电弧特性及熔池行为研究

Horizontal welding of aluminum alloys is widely used in many fields such as storage fuel tanks of heavy lift launch vehicles, pressure vessel for oil or natural gas, high-speed trains and so on. But the welding defects such as sag, overlap, undercut and porosity often emerge in the horizontal welding process for aluminum alloy plates with medium thickness. The variable polarity plasma arc (VPPA) welding technology has been applied widely in aluminum alloy welding in vertical-up position since it was invented in 1979. Its benefits include: penetration welding in single pass (6-25mm), joints without porosity, welds with high mechanical properties and so on. In our previous trials, it was found that the cutting phenomena often occurred in horizontal VPPA welding process when the aluminum alloy plate's thickness was larger than 6mm. Even if the horizontal weld can be obtained the welding defects such as sag and undercut were usually found. In previous experiments, the arc pressure was reduced by changing the geometry of cooling nozzle to create the soft VPPA. The weld pool sagging problem was partially solved. Therefore this project is to solve the key issues of soft VPPA technique including the opitimizing design, arc characterisitc and weld pool behavior of soft VPPA. The final goal is to suceffully relize the horizontal welding of aluminium alloy with thickness between 8 and 10mm. This project will further extend the mechanism and application of VPPA welding.

铝合金横向焊接在重型运载火箭燃料贮箱、石化压力容器和高铁车辆等行业中有着良好的技术需求和应用前景。但在中厚板铝合金横向焊接过程中，经常出现熔池下榻、咬边、气孔等焊接缺陷。变极性等离子弧（VPPA）焊接自1979年发明以来已经成功应用在铝合金立向焊接中，具有一次焊透6-25mm铝合金、接头无气孔缺陷、焊缝力学性能好等优点。实验发现当板厚>6mm时，VPPA横焊经常发生切割，即使能够成形，熔池下榻明显且咬边缺陷严重。前期试验中我们尝试改变压缩喷嘴形式，降低等离子弧压力，形成柔性等离子弧，能够有效控制VPPA横焊熔池。本课题针对中厚板铝合金横向VPPA焊接，设计柔性等离子弧，以克服横焊过程中由于重力作用导致的熔池下榻问题。突破柔性等离子弧优化设计、电弧特性和熔池行为等关键技术，实现8-10mm中厚板铝合金的VPPA横向焊接。课题的实现，对于进一步拓展VPPA焊接的理论体系和应用范围具有重要意义。

中等厚度铝合金VPPA横向位置焊接具有相对大的技术难度，国内外此方面的研究成果很少，理论和技术上都有待突破。本项目提出了设计电弧热源解决铝合金横焊瓶颈问题的新思路和柔性变极性等离子弧的新概念，建立了基于喷嘴结构优化和基于离子气氛围调控的柔性变极性等离子弧焊新方法，阐明了柔性变极性等离子弧的电弧特性，揭示了VPPA穿孔横焊熔池状态平衡及成形机制，阐述了横焊穿孔熔池动态行为，采用试验与数值模拟的方法系统性描述了横焊熔池建立、稳定存在及崩溃产生过程，揭示了横焊穿孔熔池建立和稳定的条件，优化了电弧热-力平衡条件关系式，首次提出铝合金VPPA穿孔横焊需要较高的能量密度和较低的电弧压力相配合新观点，设计获得了一种能量密度较高、电弧压力较低、匹配可控、椭圆形分布的新型VPPA热源模式，也揭示了氦-氩混合气氛围调控在VPPA横焊中的电弧现象及其效果，突破并最终实现了8mm和10mm厚铝合金的横焊位置VPPA穿孔型焊接，将铝合金VPPA穿孔横焊极限厚度由6.4提升至10mm，焊缝成形缺陷得到明显抑制，并对接头组织和力学性能进行了研究，阐述了穿孔横焊接头上侧和下侧热循环的差别，发现横焊接头上下侧组织及力学性能具有不对称性。对铝合金横向位置焊接气孔问题进行了探索性研究，首次进行了焊丝在线电弧阴极清理以降低焊缝气孔率新思路。研究发表学术论文9篇，其中SCI检索论文3篇，EI检索论文6篇。培养博士生2人（1名在读），硕士生5人（1名在读）。研究成果在揭示铝合金VPPA横焊热-力平焊机制，阐述熔池形态及其稳定性，实现焊缝成形控制和焊接气孔控制等方面具有科学意义、理论意义和学术价值，在航天运载贮箱焊接、舰船铝合金船体建造、化工领域产品焊接等方面具有应用前景。