Date of Award


Publication Type


Degree Name



Mechanical, Automotive, and Materials Engineering


bimetallic conductors;co-extrusion;copper clad aluminum;electric motors;electrical conductivity;severe plastic deformation


Afsaneh Edrisy



Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.


Reduction of greenhouse gas emissions can be sought after through the adoption of electric vehicles while its market demand can be improved through reducing cost and weight. This study seeks to improve efficiency through lightweighting of traction motors for electric drive systems by fabricating a bimetallic conductor denoted as copper clad aluminum (CCA). The unique composite system extends the use of aluminum within motor windings as the cladding retains the well-established surface properties of copper while its locality coincides with the concentration of current experienced within conductors operating at high frequencies. Due to the inclusion of aluminum, CCA conductors lends itself to a cost effective and low-density approach. In this research, square CCA conductors were formed through a direct cold co-extrusion process where extrusion dies were designed and manufactured. Various copper volume percentages were produced; a thinner cladding realized a poor surface quality whereas the thicker cladding exhibited seamless and uniform surfaces. Standardized testing was performed which characterized the conductor’s proportionality, resistivity, cohesion, and adhesion. A highly proportional and congruent flow of materials existed with a copper volume variance of ±1% throughout the conductor’s length. A decrease in electrical conductivity of only 1.68% IACS after the severe plastic deformation process could be attributed to the dislocation cell formation. High frequency induction heating was found to restore electrical conductivity at high temperatures and low holding times, with electrical conductivity and temperature being directly proportional. An excellent level of cohesion existed between the copper cladding and aluminum core as no seams or splits came to fruition after severe twisting. Poor adhesion was observed at the Al/Cu interface of the hard co-extruded CCA conductor due to the absence of a diffusion layer resulting in a low level of bonding. Characterization of the interface’s microstructure was investigated through optical microscopy, scanning electron microscope equipped with energy dispersive spectroscopy and microhardness testing. Overall, this study provides a novel approach in producing and heat treating copper clad aluminum conductors for electric machines which provides significant cost and weight savings compared to traditional homogenous copper windings.

Available for download on Thursday, September 26, 2024