Abstract Electrical-assisted forming (EAF), where current is directly applied to the workpiece during deformation, has been shown to dramatically reduce the flow stress of the material. In this paper, the effect of altering the Zn content in Cu specimens during EAF is investigated. Varying results were observed depending on if the threshold density, which produces significant reductions in flow stress, was surpassed. Thus, temperature increases due to resistive heating alone are not the cause of the observed effects. Once the threshold current is exceeded, the flow stress reductions increased with increasing Zn content. These results support theories regarding the physical mechanism of EAF as dislocations are able to move past alloying elements more effectively.