Low shear rate behavior at high solid fractions of partially solidified Al–8 wt.% Cu alloys

The rheological behavior at high solid fractions of a partially solidified Al–8 wt.% Cu alloy is investigated using shear tests in a Couette viscometer. The effect of grain refinement on the rheological behavior is particularly addressed. Shear experiments have been conducted at three temperatures above the eutectic: 550, 575 and 587°C. Experimental data reveal a clear difference in the shear response of the refined and unrefined alloys. The grain-refined Al–Cu alloy exhibits a quite homogeneous deformation behavior that can be related to the rheology of the viscoplastic solid phase, which is investigated through simple compression tests. On the contrary, rapid strain localization characterizes the shear response of the non grain-refined alloy. The difference in rheological behavior is related to microstructure features that are pertinent to the rheology of partially solidified alloys, solid phase morphology and grain size.