Surface Resistance Changes Due to Heat Aging of Copper and Coated Copper Alloys in Transmission and Brake Fluids

The susceptibility of electrical terminals, exposed to transmission and brake fluids for long periods to changes in surface resistance is unknown. A research project was undertaken to establish the changes in surface resistance caused by these fluids. Heat aging of selected copper alloys and coated copper alloys immersed in transmission and brake fluids was used to simulate these effects over an extended period.

Sixteen different metal samples were used in this study. Seven of the samples were bare copper alloys. Nine of the samples were coated with a commonly used electrical terminal coating. Before immersing the test samples in the fluids, surface resistance data was collected and recorded. Then the samples were placed in an oven set to 85 °C. Surface resistance data was collected at 250, 500, 750 and 1008 hours.

Of the two fluids, the brake fluid caused the greatest change in surface resistance. During the first 250 hours, the surface resistance decreased on the samples immersed in transmission fluid and increased for the samples placed in the brake fluid. A white powder that formed in the brake fluid, during the heat aging process, had an effect on surface resistance. At 1008 hours the uncoated copper alloys had unacceptable contact resistance data. The sample with a 95% tin 5% silver coating had the most acceptable results under all the conditions described in this paper.