三元保护气窄间隙GMA焊电弧的物理特性及其对金属熔化行为的影响机制

Ensuring the weld quality of narrow gap gas metal arc welding (GMAW) is a core issue. There are limitations in improving weld quality by optimizing the welding process. The investigator proposed the Ar-CO2-He ternary gases shielded narrow gap GMAW in PhD dissertation. With the addition of helium to the shielding gas, more arc heat transfers to the sidewall and sidewall penetration depth increases. However, it's short of essential research on the arc physical characteristics and its influence mechanism on the metal transfer and molten behaviors under different compositions ternary shielding gases. Owing to the limitation of the narrow gap groove and the features of the arc thermal plasma, it's hard to simply and directly observe and analyze the arc physical characteristics and metal melting behaviors by tests. In this study, the investigator intends to use numerical simulation and experimental methods to study the narrow gap GMAW for EH40 high strengh steel with the thickness of 60mm. Through establishing the arc, droplet and molten pool behaviors simulation models to analyze the thermal, force and electrical characteristics of the narrow gap GMAW arc, then based on the change of the arc physical characteristics, simulate the metal transfer and molten pool behaviors under different ternary shielding gases compositions. Finally, verifiy the simulation results by the tests and reveal the effects of shielding gas compositions on the narrow gap GMAW arc physical characteristics and its influence mechanism on the metal transfer and molten pool behaviors. The results can provide the theoretical foundation for the analysis and optimization of the welding process.

保证焊缝质量是窄间隙GMA焊中的核心问题，通过优化工艺来改善焊接质量具有局限性。申请人博士课题提出利用Ar-CO2-He三元保护气进行窄间隙GMA焊接，He气的加入使得电弧能量更多地向侧壁传输，促进侧壁熔深。然而，不同保护气比例下的电弧物理特性以及其对熔滴过渡和熔池行为的影响机制仍缺少本质上的探究。由于窄间隙坡口尺寸的限制及电弧热等离子的特点，很难简单通过试验直接观察和分析电弧物理特性和金属熔化行为。本课题拟利用数值模拟和试验相结合的方法，以60mm厚EH40钢窄间隙GMA焊为研究对象，建立电弧、熔滴及熔池行为模型，计算不同保护气比例下的电弧的热、力、电等物理特性；并结合电弧物理特性的变化，进一步模拟熔滴过渡及熔池行为；通过试验验证，最终阐明三元保护气比例对窄间隙GMA焊接电弧物理特性的影响规律，以及电弧物理特性的改变对熔滴过渡和熔池行为的影响机制。研究结果为工艺的分析和优化提供理论基础。

窄间隙GMA焊接技术可显著提高厚壁结构的焊接效率，其主要缺陷为侧壁熔合不良，项目提出利用Ar-CO2-He三元保护气进行窄间隙GMA焊接，He气的加入使得电弧能量更多地向侧壁传输，促进侧壁熔深。本项目围绕窄间隙焊接电弧物理特性及保护气对其的影响、保护气成分对熔滴过渡影响与作用机理、电弧物理特性及熔滴过渡的改变对熔池动态行为影响机制、以及高强钢厚板三元保护气窄间隙GMA焊接展开研究。研究结果表明，在窄间隙坡口的约束下，电弧物理特性发生改变，且保护气对其有显著影响，随着保护气中 He含量的增加，电弧整体温度场收缩，但中心高温区扩张，电弧轴心处电流密度增加，电流分布更加集中，工件表面的热流密度增加。随着随He或CO2含量增加，熔滴过渡频率降低，熔滴尺寸增加。建立三维瞬态熔池行为模型，通过对焊接热源的校核发现不同保护气下焊接热源不同，He含量适当地增加使得电弧热源集中系数降低，使得焊接热量更多地向热源外围传输，有利于提升窄间隙GMA焊的侧壁熔深。利用80%Ar-10%CO2-10%He三元混合气对150mm厚高强钢进行焊接，获得了成形良好的焊接接头，接头力学性能满足海洋装备服役要求。