铝/钢剪裁板电弧辅助激光熔钎焊工艺与机理研究

With the increasing applications of aluminum alloys in automobile manufacturing, the joining between aluminums and steels and other disimilar metals have become a hot area in welding research,Laser welding-brazing is a joining process of much development potential.In order to overcome the difficulties in butt weld of laser welding/brazing,an new process,namely the arc assisted laser welding-brazing process is put forward initiatively.In this process,the laser is assisted by a low power arc,but without hybrid of them, to realize the butt welding/brazing of tailored aluminum and steel blanks.By combination use of experimental measurements,numerical simulation and theoretical analysis,the following scientific problems are going to be investigated:(1) butt welding process and weld joint property for the arc assisted laser welding-brazing of aluminum/steel tailored blanks,wetting and spreading processes of liquid metal in welding,(2)thermal process,stress-strain fields,stress gradient of weld joint,residual stress and deformation characteristics and control methods，(3) the effects of addition of alloy powder and wire compositions on the interface welding metallurgy, understanding the intermetallic compound species at interface, the mechanism and control of grain growth. On these bases, the joining mechanisms and processes of the laser brazing-welding of aluminum/steel tailored sheet with the assistance of the arc are further understood, which offers a foundation for the promotion and application of this new welding technology.

随着铝合金在汽车等工业中的应用日益广泛，铝与钢等异种金属之间的连接成为焊接领域的研究热点，激光熔钎焊是很有发展潜力的方法之一。本项目创新地提出电弧辅助激光熔钎焊方法，即采用小功率电弧辅助激光（但不复合）对铝/钢异种金属剪裁板进行熔钎拼焊，从而解决对接焊缝成形难题。通过采用试验测试、理论和数值分析相结合的方法，主要研究：(1)铝/钢剪裁板电弧辅助CO2激光熔钎拼焊工艺与接头性能，焊接过程液态金属的浸润与铺展过程；(2)铝/钢异种金属熔钎焊热过程及应力、应变场，接头应力梯度，残余应力和变形特点及工艺控制措施；(3)合金粉末、焊丝成分对铝/钢熔钎焊接头界面焊接冶金的影响规律，明确界面金属间化合物种类、晶粒生长机制及其控制。综合以上研究，深入理解并进一步明确铝/钢剪裁板电弧辅助激光熔钎拼焊连接工艺与机理等基本科学问题，为推广应用提供依据。

本项目针对铝/钢薄板对接焊难题，提出了电弧辅助激光熔钎焊方法,实现了铝合金/镀锌钢板电弧辅助激光对接熔钎焊连接。系统地研究了焊接工艺参数对微观组织、接头成形及力学性能的影响；通过建模及数值分析方法，分析了铝/钢对接接头的液态金属润湿铺展行为、界面金属间化合物生长行为、焊后的残余应力及变形。.焊接工艺研究方面，电弧辅助激光方法可实现铝合金/镀锌钢对接接头的单面焊双面成形。通过多组正交试验获得优化的工艺参数，当激光热输入1.0~1.2kJ/cm，电弧电流13~16A，热源间距10~20mm，可获得良好的焊缝成形。铝/钢界面金属间化合物层由Fe2Al5和Fe4Al13两层化合物组成，厚度约6~16μm。金属间化合物厚度随热输入的增加呈线性增长，接头抗拉强度由焊接热输入、浸润铺展宽度及金属间化合物厚度所决定，接头的最高抗拉强度为163MPa，是相同激光功率单激光熔钎焊接头抗拉强度的1.3倍，接头断裂为韧脆混合断裂模式。.焊接物理建模与数值分析方面，进行了铝/钢电弧辅助激光对接熔钎焊的润湿铺展行为的试验研究和数值分析，并用 VOF方法追踪自由表面，发现引入辅助电弧后，母材表面温度场分布范围变大，金属熔化量增多，使得熔池中液态金属的流动性增强，改善了液态金属在钢表面的润湿铺展效果。在铝/钢对接熔钎焊连接机理及界面行为方面，采用蒙特卡罗方法（MC）结合元胞自动机（CA）方法，研究了非平衡条件下，界面处金属间化合物生长及取向并对焊接界面金属间化合物组织的演变机理进行分析，金属间化合物厚度由峰值温度、冷区时间及温度梯度共同决定。针对铝/钢对接薄板熔钎焊的应力-应变及热变形进行研究，辅助电弧的加入可以减小加热及冷却过程塑性应变的分布范围，有助于降低残余应力和焊接变形。通过正交试验分析，研究了焊接参数对接头纵向残余应力和变形影响的显著性和规律性,通过刚性固定拘束调控，确定了夹具拘束距离的优化范围。