Viscosity and Solidification of the Al_100 – хCu_х (х = 5, 10, 17, 25 at %) Melts

Abstract—

The method of damped torsional vibrations in the temperature range from liquidus to 1200°C was used to study the temperature dependences of the viscosity of melts of the Al–Cu binary system containing 5, 10 (hypoeutectic), 17 (eutectic), and 25 (hypeutectic) at % of copper. For all compositions near a temperature of 800°C, a deviation of the viscosity polytherms from the Arrhenius dependence was found, which is associated with the features of the structural state of the melts. A comparative study of samples obtained by melt spinning with different structural states, depending on temperature (750 and 1200°C) and alloy composition, was carried out using X-ray diffraction analysis and electron microscopy. In a hypoeutectic alloy with a higher copper content, regardless of the melt quenching temperature, a more supersaturated Al(Cu) solid solution is formed. The temperature treatment of melts before quenching affects the structure and mechanical characteristics of solid samples formed during spinning. All samples are crystalline, represented by α-Al, Al₂Cu phases. The effect of heat treatment of melts on the morphology, size, and lattice periods of the structural constituents of alloys of all compositions is shown. The selected modes are reflected in the average value of the microhardness of the alloys. Hypoeutectic alloys with a higher copper content have higher microhardness values due to a more dispersed structure, a larger volume fraction of finely dispersed eutectics, and a more supersaturated Al(Cu) solid solution. In hypereutectic alloys, higher values of microhardness are in alloys with a higher concentration due to a larger amount of the hard component—Al₂Cu aluminides.