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Modern automotive transmissions contain copper and copper alloys in the form of washers, bushings, brazes and electrical components. Corrosion that occurs with any of these components especially with electrical contacts can result in a malfunction of the vehicle control systems and loss of vehicle drivability. The compatibility of transmission lubricants with copper and copper alloys is an increasingly important consideration in the design of new additive technology. Traditional methods for monitoring corrosion processes and mechanisms in real time can be both time consuming and challenging to interpret, especially when evaluations at multiple temperatures are required. This work challenges some of the industry-held beliefs around lubricant additive corrosion processes, especially at elevated temperature (>130 °C).

In this study, the copper corrosion rates of commercially available lubricants used in electrified and conventional transmissions are measured in both vapor and solution phases simultaneously using an updated version of our previously reported wire resistance test [1]. Unlike the commonly used copper strip tests (versions of the ASTM D130) that generally require high temperatures and long times to differentiate the corrosivity of fluids, the wire resistance test is sufficiently sensitive as to allow real time assessment, thus enabling an efficient and cost-effective way to screen lubricant chemistries over a range of potential operating temperatures. The results of even our small study underscores the importance of understanding both the vapor and solution corrosion across a wide range of temperatures.