钢/铝搭接激光深熔焊接头中脆性Fe-Al化合物的调控及机理研究

This project originating from the great demands for steel/aluminum structure parts in fields of modern transportation tools in order to realize the lightweight vehicle structure, considering such the problems as the generation of brittle Fe-Al compounds need be solved urgently for steel and aluminum dissimilar metal welding quality, puts forward deep penetration laser welding technology by adding power coating to steel/aluminum interfacial layer with lap joint applied with steel sheet on the top and aluminum sheet at the bottom, then, the selection design of coating powder element is carried out by the use of the first-principle calculations,thus phase composition of Fe-Al compounds in the steel/aluminum interface is regulated with the addition of powder coating, meanwhile, the diffusion of aluminum into the molten pool is limited due to the faster cooling rate in deep penetration laser welding, thus layer thickness of the Fe-Al compounds is reduced, in addition, morphology and distribution of Fe-Al compounds are improved by controlling heat transfer from steel to aluminum and flow behavior of molten pool composed of the mixing of liquid steel and aluminum.The design criterion of coating powder element will be explored, the change rules of temperature field distribution and dynamic behavior of the molten pool will be studied, and the growth mechanism of Fe-Al compounds will also be studied. Finally the qualitative relationship between phase composition, morphology, distribution, layer thickness of Fe-Al compounds and mechanical property of the joint will be established, thus brittle Fe-Al compounds in steel/aluminum lap joint for deep penetration laser welding can be regulated. Through the research, the project results will enrich dissimilar metal welding forming theory and provide new idea and theoretical basis for the development of steel/aluminum dissimilar metal structure parts laser welding application.

本项目面向现代交通运输领域为实现车辆减重对钢/铝结构件的迫切需求，针对钢/铝优质高效焊接易生成脆性Fe-Al化合物的难题，提出钢上铝下搭接、钢/铝层间添加粉末涂层的激光深熔焊技术，采用第一性原理计算方法，选择设计涂层粉末元素；利用粉末涂层，调控钢/铝界面Fe-Al化合物的相组成；利用激光深熔焊冷却速度快的特点，限制铝向钢熔池扩散，减少Fe-Al化合物的层厚度；通过控制钢/铝层间热量传递及钢、铝液混合熔池流动，改善Fe-Al化合物的形态与分布。项目探索涂层粉末元素设计准则，研究焊接接头温度场分布与熔池动态行为变化规律，以及Fe-Al化合物的生长机理，建立Fe-Al化合物相组成、形态、分布、层厚度与接头性能的定性关系，实现激光深熔焊钢/铝搭接接头中脆性Fe-Al化合物的可调控。通过本项目的研究，其成果将丰富和完善异种金属焊接成形理论，并为发展钢/铝结构件激光焊接的推广应用提供新思路和理论依据。

本项目面向现代交通运输领域为实现车辆减重对钢/铝结构件的迫切需求，针对钢/铝优质高效焊接易生成脆性Fe-Al化合物的难题，探索了钢上铝下搭接、钢/铝层间添加粉末的激光深熔焊技术，从第一性原理计算粉末元素设计出发，建立粉末原子择优占位与体系延/脆性之间的关系，探索粉末原子对Fe-Al化合物脆性影响规律，发现脆性Fe-Al化合物限制钢/铝接头力学性能，其脆性的电子结构根源在于Al(s)，Al(p)和Fe(d)之间的轨道杂化，而添加粉末元素改变金属间化合物(IMCs)的电子结构，接头性能改善与其形成IMCs的延/脆性密切相关；研究焊接接头温度场分布与熔池动态行为变化规律，以及Fe-Al化合物生长机理，发现合理控制钢/铝界面元素扩散反应过程，保证钢/铝界面均匀反应，是调控钢/铝激光深熔焊接头脆性Fe-Al化合物层厚度的关键，而激光热源对脆性Fe-Al化合物的形态与分布产生重要影响；通过添加粉末元素种类、中间层厚度及激光焊工艺等参量对钢/铝焊缝形貌、焊接缺陷及接头性能影响规律，及钢/铝界面及其附近熔池区Fe-Al化合物影响规律等研究，建立接头性能与界面IMCs相组成、形状、分布、层厚度的定性关系，基于脆性IMCs调控，改善钢/铝接头性能。运用研究获得的成果为指导，拓展了不局限于钢/铝异种金属添加金属箔片和激光热源摆动焊接等研究。通过本项目的研究，其成果丰富和完善异种金属焊接成形理论，并为发展钢/铝结构件激光焊接的推广应用提供新思路和理论依据。