Frequency-dependent material properties of copper and aluminum alloys

In this paper, the dynamic behavior of copper and aluminum alloys as used in electric drive units is investigated. Isothermal frequency sweeps are performed from 0.1 up to 50Hz at temperatures of up to 400 degrees C. An evaluation of the test results at a constant frequency of 1Hz shows a decrease in the storage modulus and an increase in the material damping. Considering all frequencies, a supplementary frequency dependency related to the material composition is detected. The lower the volume fraction of the alloying elements, the higher the impact of temperature and frequency on the material properties. The variations of the material parameters allow applying the time temperature superposition principle to estimate the dynamic behavior beyond the limited tested frequency range and temperatures by fitting the Williams-Landel-Ferry equation. Additional thermal aging of CU-ETP specimens does not affect the storage modulus, but diminishes the material damping. The findings show that each material has to be tested with regard to its respective application, material composition and manufacturing process. Furthermore, they demonstrate the relevance of considering the frequency-dependent material properties of low-alloyed copper and aluminum, especially in case of temperatures above 100 degrees C.