石墨熔池烧蚀行为对钎料流动铺展的影响机理研究

Resistance brazing in nonmetal weld pool is different from heat conduction welding and deep penetration welding . It is applied to processing the conductor of heating cables which is made of jointing copper wires and Ni alloy wires. Beacause the producer of welding for dissimilar metal is very complex, transient behavior of brazing weld pool is difficult to be controlled. This effect on properties of conductor of heating cables and is disadvantaged to processing the conductor by automatic machine. In order to explore the influence of welding mechanism,.firstly, the ablation mechanism of weld pool in low temperture is discussed to analyse the ablation morphology of the grahite composite in the micromechanical scale and surface erosion law in the macroscale. Secondly, the thermal conduction mechanism is built to discuss the wear and erosion of bore and its influence to temperature in weld pool. Finally, with analyzing the action features of heat source in brazing and latent heat and impact of thebase metal, a transient three-dimensional model of brazing weld pool for copper and Ni alloy is established on the basis of theories of fluid dynamics and heat transfer. The flow behavior of filler metal in brazing is discussed. The method and results are important to improving welding process parameter and the joint’s properties.

深熔钎焊技术是界于热导焊和深熔焊之间的一种特殊焊接方式，主要用于发热电缆领域制造不等直径Cu/Ni基异种金属丝对焊接头。由于深熔钎焊机制复杂，降低了焊接过程自动化的可控性，影响了接头组织结构和性能。因此，为了深层次理解焊接过程的物理实质，本项目研究石墨熔池的低温烧蚀机制，建立在微观、宏观上的石墨烧蚀模型，分析探讨石墨微观表面烧蚀形貌和宏观表面烧蚀衰退变化对界面接触电阻和焊接热的影响规律；研究石墨熔池烧蚀中传热机制，分析烧蚀磨损和摩擦磨损造成石墨熔池圆柱内孔形状变化及对熔池温度场变化与分布的作用；在综合考虑热源作用特点、焊接母材冲击等因素的基础上，建立钎料流体动力学模型，研究烧蚀条件下热力分布影响钎料流动铺展的规律。研究方法和结果将对揭示焊接过程中多场耦合作用机理、优化深熔钎焊工艺、提高过程自动化及焊接质量具有重要的理论意义和工程价值。

发热电缆的线芯由不等直径的Cu金属丝（冷线，0.4～1.13mm）和Ni基合金发热丝（热线，0.3～0.85mm）配对经深熔钎焊而成。发热电缆线芯的深熔钎焊是介于热导焊和钎焊之间的一种特殊焊接方式，主要利用铜电极与带孔石墨焊接池间的接触电阻生热熔化Ag基钎料，进而实现Cu/Ni基金属丝在带孔石墨焊接池中的钎焊。因此，研究接触界面接触和钎料铺展行为是明晰发热电缆线芯的深熔钎焊机理的关键。本项目通过分析讨论不同状态条件下石墨焊接池表面形态，建立基于G-W接触理论的界面接触模型，通过数值计算研究接触形貌、接触压力及接触面积等参数之间的相互影响，结果表明普通石墨焊接池由于表面粗糙度大于精细石墨熔池，在较短接触距离内达到相应的接触面积。建立石墨焊接池静态分形接触电阻和动态烧蚀接触电阻的数学模型，深入研究石墨微观表面烧蚀形貌和宏观表面烧蚀衰退变化对界面接触电阻和焊接热的影响作用，结果表明与普通石墨焊接池因材料差异、表面粗糙、孔隙率高等特点，烧蚀作用较精细石墨焊接池明显对界面接触电阻的影响大。建立钎料流体动力学模型，研究烧蚀条件下热力分布影响钎料流动铺展的规律，结果表明焊接过程电磁力对钎料流动的起主要作用，表面张力的影响较弱；因铜丝侧的温度低于镍丝侧的温度，导致铜丝侧的钎料流速高于镍丝侧的流速，钎料流动铺展优于镍丝侧。本项目的研究理论方法和基础数据对揭示焊接过程中多场耦合作用机理、优化深熔钎焊工艺、提高Cu/Ni基金属丝对焊质量具有重要的理论意义和工程价值。