Electro-magnetic melt pool displacement for joining dissimilar materials

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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.