强对流条件下的钎料润湿铺展与界面传质行为交互作用研究

The spreading/wetting behavior of liquid filler metal droplet was conducted in strong convection condition under high external heat flux input and pressure. There is some difference between arc brazing processes between traditional brazing processes in which the spreading/wetting behavior was only controlled by interfacial surface tension of solid-gas, liquid-gas, and liquid-solid. In addition, the joint mechanical properties were decided by the wetting phenomenon and interfacial transportation behavior during joining process. In this project, the study method of the combination of fusion brazing test and arc sessile drop test was used to learn the influence factor and law of filler metal wetting property, spreading kinetics, interfacial microstructure during arc brazing process. The spreading/wetting experiments of same brazing filler are also conducted and used to comparison. The interfacial reaction wetting theory and the mathematic model of fluid flow and thermal conduction in welded pool was also used as references. The project focuses on discussing the arc heat flux and arc pressure on the fluid flow and dynamic spreading behavior of filler metal droplet and establishing the theory model of dynamic spreading kinetics. The correlation between the dynamic wetting angle, solid-liquid-gas frontier moving speed and the interfacial transport phenomenon and chemical structure evolution happened in the frontier should be learned. Finally, the controlling factor (heat flux controlling or interfacial reaction controlling) of the wetting and spreading during arc brazing process could be obtained. Finally, the difference of spreading/wetting behavior and generation mechanisms between arc brazing and tradition brazing processes will be given. The results of the project can provide foundation data for the development of new materials and new technology of fusion brazing process, and to promote the development of spreading/wetting theory of brazing process.

熔钎焊过程中，钎料液滴的润湿铺展是在外部热流及压力作用下的强对流条件进行的，和传统钎焊中仅由固-气、液-气、液-固等界面张力的力学平衡决定其润湿铺展过程存在一定差异，而钎料液滴的润湿铺展及界面传质行为之间的交互作用又决定了熔钎焊接头的成形与力学性能。本项目试图采用熔钎焊试验与电弧座滴法相结合的方式，并对比传统钎焊条件下液态钎料润湿铺展试验结果，借鉴传统钎焊界面润湿理论以及传统熔化焊熔池流动及传热过程的数学模型，考察钎料液滴的润湿性，铺展动力学，界面传质行为、微结构及其影响因素和规律。重点探讨电弧热流和电弧压力的施加对钎料液滴内部流场及其动态铺展行为的影响，建立能够正确描述强对流条件下液态钎料铺展动力学的理论模型，研究宏观上测定的液态钎料动态润湿角、三相线移动速度和微观上发生在固-液-气三相线附近的传质行为与物相结构演变之间的联系，从而精确掌握熔钎焊过程铺展润湿的主控因素（热对流控制或界面传质行为控制），最终获得熔钎焊和普通钎焊两种状态下液态钎料润湿铺展行为的差异及其产生机制。研究结果一方面可为熔钎焊新材料新工艺的开发提供基础数据和理论指导，也可促进钎焊润湿铺展这一基础理论的发展。

采用熔钎焊工艺对镀层薄钢板或铝/钢异种金属材料接头进行连接受到广泛的重视，在熔钎焊连接过程中易形成液态钎料填缝性能下降，冶金反应不充分现象，使得焊缝存在轮廓尺寸异常，结构不致密，成形不美观，接头存在应力集中，力学性能下降等诸多冶金和力学质量问题。本项目采用熔钎焊试验与电弧座滴法相结合的方式，并借鉴传统钎焊界面润湿理论以及传统熔化焊熔池流动及传热过程的数学模型，考察了CuSi3Mn1、AlSi5和AlSi12等钎料液滴的润湿性，铺展动力学，界面传质行为、微结构及其影响因素和规律，发现随熔钎焊热输入（电弧电流、电压、送丝速度和激光功率等）的增加，钎料润湿铺展性能提高，并且相比传统真空钎焊工艺，其传热传质行为更加剧烈，界面可能生成不同形态、大小及厚度的Fe5Si3(Cu)、FeAl3及Fe2Al5等化合物，从而影响接头显微硬度、拉伸和弯曲等力学性能。重点探讨了电弧热流和电弧压力的施加对钎料液滴内部流场及其动态铺展行为的影响，建立了能够正确描述强对流条件下液态钎料铺展动力学的理论模型，计算结果表明，控制钎料液滴铺展的主要因素除了电弧压力以外，还有钎料液滴单位体积受到的重力及表面张力等。并且其流动在电弧轴线下方呈现由上至下，而在液/固界面处向左右两侧流动的趋势，与常规TIG熔化焊接熔池内部的环流流场呈现不同的规律，有利于钎料液滴的横向铺展。发现电弧的强对流作用有利于钎料内部成分的均匀分布，导致界面化合物产生断裂行为。获得了宏观上测定的液态钎料动态润湿角、三相线移动速度和微观上发生在固-液-气三相线附近的传质行为与物相结构演变之间的联系。同时，针对TIG钎焊、CMT钎焊和激光钎焊试验对上述研究成果进行了验证，并且所得研究成果成功在液力变矩器高强铝合金/钢异种材料连接中实现工业化应用。