Application of Matthiessen's rule to resistivity measurement and behaviors of Fe and Si in A1050 rolled sheets

Application of Matthiessen's rule to resistivity measurement was examined. An induced empirical relation between resistivity and resistance ratio is accurate enough for measurement of the resistivity of A1050 rolled sheets. The resistivity change with various heat treatments leads to the following facts. Some parts of Si in the alloy precipitate during cold rolling as elemental Si and the amount of the precipitates increases by annealing below 250°C. Dissolution of precipitated Si completes at 400°C. Most parts of Fe in the alloy have precipitated. Fe further precipitates by annealing below 400°C after cold rolling. The precipitates dissolve by annealing above 400°C up to the equilibrium solubility in Al-Fe binary diagram. Precipitation of Fe and Si is accelerated by cold rolling, The equilibrium solubility of Fe lowers with increasing Si content. Activation energy for a resistivity decrease with isothermal aging above 400°C agrees with that of diffusion of Fe in Al. Impurities other than Fe and Si are always in solution comparing chemical compositions and solid solubilities of the impurities.