SUNConferences, COMA '13

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Combined Laser Beam Braze-Welding Process for Fluxless Al-Cu Connections
Peter Plapper, Tobias Solchenbach

Last modified: 2013-08-20

Abstract


The paper describes an innovative, laser based joining method for dissimilar Al-Cu connections. The main objective is the improvement of the mechanical and electrical properties of the joints.


Storing electrical energy plays the key role in the E-Mobility. Li-Ion batteries (LIB) provide high energy and power density as well as excellent cycle durability.A battery stack consists of multiple LIB cells in parallel and serial connection. Therefore, the electrical connection tabs, which are made of aluminum and copper, have to be joined. Hence, beside the Al-Al and Cu-Cu, also the Al-Cu connection is important.Due to the small thickness of the tabs (0.4 to 0.1 mm) conventional mechanical fastening, e.g. bolting, known from prismatic LIB cells, would destroy the tabs. Therefore, a non-contact thermal joining method is desirable.The challenges for thermal joining of dissimilar Al-Cu connections are evident:Brittle intermetallic compounds (IMC) occur. Due to their complex atomic structure, dislocating is hindered and, thus, stresses cannot be relieved. Above a critical seam width of 10 ┬Ám, IMC strongly reduce the mechanical properties of the joint.Compared to pure Cu and Al, the electrical resistance diminishes for alloys between the two. Periodical formation of intermetallic superlattice structures has positive influence on the electrical conductivity.
The present paper introduces a joining method which addresses the above mentioned challenges. On the one hand, the objective is to reduce the IMC phase width, on the other hand to form a homogenous but thinIMC phase in the joining area. Therefore, a combined laser welding and brazing process is applied, where the melted Al layer wets the solid state cu layer in overlap configuration.The paper shows the latest experimental results of these investigations.

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