Electrical resistivity measured by millisecond pulse-heating in comparison to thermal conductivity of the aluminium alloy Al-7Si-0.3Mg at elevated temperature
E. Kaschnitz, W. Funk and Th. Pabel
Electrical resistivity of two grades of aluminium alloy Al-7Si-0.3Mg was measured by millisecond pulse-heating in the temperature range from room temperature to 450 °C. The first grade is an industrial standard material; the second is high purity grade with a low content of Ti and Zr. The measurement of electrical resistivity as a function of specific enthalpy was combined with specific heat capacity measurements by differential scanning calorimetry to obtain the relation between resistivity and temperature. This is necessary, since a contactless temperature measurement was not possible due to the low sensitivity of our pyrometers of the millisecond pulse-heating system. Additionally to electrical resistivity and specific heat capacity, density at room temperature, thermal diffusivity, and thermal expansion was measured. From these results, thermal conductivity was calculated. Comparing thermal conductivity to electrical resistivity, the Lorenz number can be computed for the entire temperature range.
The higher purity alloy shows a significant lower electrical resistivity and an equivalent increase in thermal conductivity. Different forms of the Wiedemann-Franz law found in the literature were compared using the results of the measured thermophysical properties, showing that the use of the simplest form gives the best match for this highly conducting aluminium alloy.
Keywords: aluminium alloy Al-7Si-Mg, electrical resistivity, elevated temperature, Lorenz number, millisecond pulse-heating, specific heat capacity, thermal conductivity, thermal expansion