Influencing the electrical properties of laser beam vacuum-welded Cu-Al mixed joints

Abstract

A great potential for lightweight construction, above all in the field of electromobility, lies in the substitution of copper by aluminum. It is, moreover, possible to apply aluminum as a conductor and copper as a contact material (firmly bonded joining). During the fusion welding of this joint, brittle intermetallic phases occur which negatively affect the mechanical and technological properties of the joint. The high hardness of the intermetallic phases exerts a great influence on the load-bearing capability. Also, the electrical resistance of most intermetallic phases is one order of magnitude higher than that of the pure materials. The state of the art, so far, has put the focus only on the identification of the crack-sensitive intermetallic phase. External influential factors, such as temperature, current-feed, and time, bring about the change of the joining zone structure by diffusion and electromigration. Moreover, a temporal change of the technological properties (further increase of the electric resistance and reduction of strength) of the dissimilar material joint will occur. Findings about this behavior will allow one to draw conclusions about the expected lifetime of the joints. The research shows that the mixing during the welding process shows a great influence on the formation of intermetallic phases and thereby on the properties of the joint.