Copper Electrode Degradation Due to the Resistance Welding of Aluminum. A Trident Scholar Project Report, No. 267

摘要

This Trident research project focuses on increasing the life of copper electrodes used in the resistance welding of aluminum work pieces employed in the automotive and aerospace industries. When the copper and aluminum make contact at the interface, there is some undesirable mixing which results in the formation of a copper-aluminum eutectic phase. The welding temperature is high enough to melt the aluminum, but the eutectic phase has a lower melting temperature than either pure copper or pure aluminum. During subsequent welds the eutectic melts away, causing the copper to degrade rapidly and the electrode lifetime to be shortened. As an alternative, electrodes made from copper alloys with very high melting temperature refractory metals, such as molybdenum, niobium, and chromium, have been fabricated. Since the refractory metals are not readily soluble in copper, it was necessary to use unconventional processing techniques to produce electrodes of uniform composition. These techniques included spray forming, rapid solidification, ion implantation, laser cladding, and mechanical alloying. The new processing techniques allow for a higher concentration and a more uniform distribution of the refractory metal, as confirmed by metallurgical analysis involving optical and electron microscopy. The electrodes were tested for homogeneity, conductivity and welding lifetime. Recommendations are provided concerning alloy selection for improved electrode performance.