Achieving superior mechanical properties in friction lap joints of copper to carbon-fiber-reinforced plastic by tool offsetting

Abstract

It is a challenge to achieve a sound welded metal/carbon-fiber-reinforced thermoplastic (CFRTP) joint with high strength and few bubbles. In this study, sound lap joints of Cu and CFRTP were obtained by friction lap joining (FLJ) directly at rotation rates of 600–2000rpm, with the welding tool at the joint center and offsetting the tool 7mm away from the center toward the retreating side, respectively. Tool offsetting reduced the non-uniform temperature distribution in the lap joints resulting from the high conductivity of Cu, which not only enhanced the tensile shear force from 0.89–2.25kN to 1.71–3.54kN, with the maximum increasing rate of 135%, but also reduced the bubble area to only 19% of the original level of 2000rpm. It is the first time to report a high-quality Cu/CFRTP joint with a high strength and few bubbles. The large increase of the strength after tool offsetting was attributed to the increase of the joining area, the decrease of bubbles and the decrease of the CFRTP degradation. The details on the generation, quantitative distribution and expulsion of the bubbles in the FLJ joints were discussed.