Pilot scale production of copper clad aluminum e-motor windings through combined extrusion-rolling

This study investigates the manufacturing of a copper clad aluminum (CCA) wire in the novel 3x2 mm rectangular profile required for hairpin windings: the next generation of conductors used in traction motors for electric vehicles. The focus of the article is on processing a CCA wire with the required rectangular profile that can be used for traction motor testing while its potential benefits are briefly detailed. To produce research quantities of CCA wire, a pilot-scale forming process consisting of co-extrusion and wire rolling was used to produce the bimetallic wire. The effect of various co-extrusion parameters such as semi-die angle, copper volume percentage, speed, billet length and design were investigated. Characterization of the copper, aluminum and Al/Cu interface microstructure was evaluated through optical microscope (OM) and scanning electron microscope (SEM). The large reduction in area from processing resulted in an excellent level of cohesion and adhesion between materials through severe testing with accordance to ASTM B566. No separation or gaps existed at the interface between materials observed through an OM in both tensile and compressive interface regimes; this could be attributed to the diffusion zone that developed after co-extrusion. The level of adhesion was also examined as the fracture surface showed no separation between the Cu and Al layers. As there is no debonding at the interface, power losses are not expected to occur after the short wires are bent to a coil and used in traction motor testing of the rectangular profile.