Electro-magnetic melt pool displacement for joining dissimilar materials

不同材料的连接是生产各种工业应用中功能和重量优化结构的关键挑战。特别是对于汽车行业的轻量化结构，铝与钢的连接是非常重要的，因为这些材料不能用现有的焊接工艺可靠地连接。目前使用的连接技术如机械连接或胶粘剂连接都存在一定的缺点，因此还需要开发新的连接技术。本申请项目旨在为开发一种新的连接技术获取基础知识，该技术将基于材料粘合和互锁产生不同材料的连接。该方法是基于脉冲激光辐射在第一个接合体上产生局部熔池，并通过电磁感应力将该熔池位移成第二个接合体的空心形状。到目前为止，这种电磁感应力仅用于连续焊接过程。因此，该项目的目标是获得关于电磁感应洛伦兹力对短期存在熔池（存在时间<0.5 s）的可控性的基本认识。通过使用激光束的瞬态脉冲形状，必须达到熔体中的温度水平，以避免熔体池过热和第二个接合伙伴的熔化，以限制众所周知的问题，如金属间相或开裂。为了调整时间瞬态能量输入，必须计算熔池内的热平衡。因此，现有的结合电磁力和熔池对流的有限元模型必须进一步发展并适应脉冲激光治疗。在项目结束时，对接头应使用进行金相和电子显微镜以及力学测试，以了解温度循环、所得材料性能和接头强度之间的相互依赖关系。

Joining of dissimilar materials is a key challenge in the production of functionally and weight optimized structures for a variety of industrial applications. Especially for lightweight constructions in the automotive sector, the connection of aluminum with steel is of high importance, since these materials cannot be joined reliably with established welding processes. Currently used joining techniques like mechanical joining or adhesive joining are associated with certain disadvantages, so that novel joining technologies are still needed to be developed.The applied project aims at obtaining basic knowledge for the development of a new joining technology, which will produce joints of dissimilar materials basing on material bonding and interlocking. The approach is based on the generation of a localized melt pool by pulsed laser radiation on a first joint partner and the displacement of this melt pool by electromagnetically induced forces into a hollow shape of a second joining partner. Up to now, such electromagnetically induced forces are only used for continuous welding processes. Objective of the project is therefore to gain a basic understanding about the controllability of a short-term existing melt pool (existence time <0.5 s) by electromagnetically induced Lorentz forces.By using a transient pulse shape of the laser beam, a temperature level in the melt must be achieved, which avoids overheating of the melt pool and a melting of the second joining partner in order to limit well-known problems such as intermetallic phases or cracking. For the adjustment of the time transient energy input, the heat balance within the melt pool must be calculated. For this reason, an existing FEM model combining the electromagnetic forces with the melt pool convection must be further developed and adapted for pulsed laser treatment. At the end of the project, metallographic and electron microscopy as well as mechanical testing of joints shall be used to gain an understanding of the interdependencies between the temperature-cycle, the resulting material properties and the strength of the joints.