Apparent Viscosity and Structure in Partially Solidified Al-Cu Alloys

Abstract

The apparent viscosity was measured as the value of torque by stirring continuously by a rotor from the molten state to the desired temperatures partial solidified at constant cooling rate in Al-Cu alloys.
By the stirring, primary α solid particles or dendrites were broken to a mushy state and the structure was observed by water quenching from the stirring temperature.
The results obtained were as follows.
(1) With increasing Cu concentration, the increase in the value of torque shifted to lower temperatures below the liquidus line and became retarded.
(2) With increasing Cu concentration, the value of torque showed increase at a small volume fraction of the solid phase.
(3) As the solid particles became finer with increase in Cu concentration, the value of torque showed a marked increase against the volume fraction solid.
(4) Regardless of the Cu concentration, solid particles became finer and spherical with the progress of stirring.
(5) Solid particles in the mushy state were not only crushed but also aggregated by mechanical stirring.