RHEOLOGY OF SEMISOLID AL-4.5-PERCENT CU-1.5-PERCENT MG ALLOY

The rheological behavior of semisolid Al-4.5%Cu-1.5%Mg alloy slurry was investigated by using a slightly modified Couette viscometer to conduct three different types of experiments. In continuous cooling experiments the apparent viscosity of the sheared slurry increased with increasing volume fraction solid and increasing cooling rate, and decreased with increasing shear rate. The average particle size of the alpha phase decreased with increasing shear rate, increasing cooling rate, and increasing copper content in the alloy. The rate of decrease in particle size with increasing shear rate decreased with increasing cooling rate. In isothermal experiments at constant volume fraction solid and shear rate, the apparent viscosity decreased with increasing isothermal holding time, reaching a "steady state" value after about 1000 s. The normalized specific particle surface area also decreased with isothermal holding time, reaching "quasisteady state" values. In isothermal experiments at constant volume fraction solid and variable shear rate, the steady state apparent viscosity of a semisolid alloy slurry decreased with increasing shear rate and decreasing volume fraction solid, while the normalized steady state specific particle surface area decreased and the normalized steady state average particle size increased. A state equation is proposed which fits reasonably well the experimental points obtained in this third group of experiments.