Viscosity of molten Cu–M alloys (M = Ni, Al)

The viscosities of the molten Cu–Ni and Cu–Al alloys were measured using an oscillating crucible method over the entire composition range to obtain reliable data and examine composition dependence precisely. The measured viscosities of all alloys showed good consistency in heating and cooling processes, and the logarithmic viscosities showed good Arrhenius-type linearity, indicating that no considerable change in the liquid structure occurs in the temperature range studied. The composition dependence of the viscosity of Cu–Ni alloys was close to that defined by the additive law of logarithmic viscosities of pure components, whereas the composition dependence of the viscosity of Cu–Al alloys was far from that defined by the additive law, where the logarithmic viscosity increased with the addition of a small amount of Al and showed a peak. Over the peak concentration, the logarithmic viscosity monotonically decreased with further addition of Al. Deviations from the additive law of logarithmic viscosity of molten Cu–Al alloys at 1773 K were maximum at low Al concentrations; in contrast, the excess molar volumes of Cu–Al alloys showed minimum at low Al concentrations. The increase in viscosity in the low-Al-concentration region of the Cu–Al alloy is attributed to the decrease in the interatomic distance, which reduces the freedom of movement of atoms.