Life and failure of oriented carbon nanotubes composite electrode for resistance spot welding

In view of the poor weldability of electrodes in resistance spot welding (RSW) of galvanized steel sheets, the life of oriented multi-walled carbon nanotubes reinforced Cu matrix composites (Cu@MWCNTs/Cu) electrodes was studied, in which Cu coated multi-walled carbon nanotubes (MWCNTs) are arranged along the flow direction of working electric/force. By analyzing the macro/microscopic morphology, microstructure, hardness, texture and composition of the failed composite electrodes and the commercially CuCrZr electrode, the mechanism of the weldability enhancement and failure of electrodes was discussed. The results show that the life of Cu@ MWCNTs/Cu electrodes (2150 welds) is 3 times longer than that of CuCrZr electrode (600 welds), and the degradation rate is much slower. The hardness of Cu@MWCNTs/Cu electrodes is 30–40Hv higher. The content of recrystallized and recovery grains of Cu@MWCNTs/Cu electrodes is less. This is due to the pinning effect of MWCNTs, and straight and long MWCNTs are arranged along the electrical/force direction. These improve the hardness, mechanical properties, conductivity, and resistance to thermal deformation, cracking, and pitting of Cu@MWCNTs/Cu electrodes, which effectively slows down the failure rate and makes the spot welding life of Cu@MWCNTs/Cu electrodes longer. This work provides a new idea for the application of CNTs/Cu composites.