Rheology of partially solidified hypoeutectic aluminum copper alloys

This study presents oscillatory and rotational viscosity measurement results on Al-Cu alloys with the goal of achieving effective viscosity data of partially solidified alloys from fully liquid to nearly fully solid state. Rotational viscosity measurements indicate fragmentation of dendrites and a concomitant sudden drop in viscosity of the solid–liquid two-phase mixture upon cooling and increase in solid fraction. This measurement artifact is avoided with oscillatory measurements. The viscosity of partially solid Al-Cu over the hypoeutectic range is nearly composition independent when evaluated as a function of solid fraction. The oscillatory measurements yield a complex viscosity with the real part reflecting the elastic behavior and the imaginary part indicating the viscous part of the viscosity behavior. The measurements of the phase angle in this study reveal that the rheological behavior of the solid phase in the liquid–solid two-phase region resembles that of a liquid more than that of a solid phase. Highlights Oscillatory rheology is shown to be better suited to characterize partially solidified metal alloys than rotational rheology. The viscosity of the liquid phase does not change measurably during solidification despite an increase in the solute content. The solid phase in the liquid–solid two-phase region behaves rheologically more like a liquid than a solid.