Effects of Cooling Rate and Grain Refiner on Semi-solid Rheocasting Slurries of Al-Zn-Mg Alloy

Swirled Equilibrium Enthalpy Device (SEED) process was used to make Al-4.8Zn-1Mg semi-solid slurries. The effects, about cooling rate and Al-5Ti-1B on semi-solid slurry microstructure and temperature field, were studied in detail. It was found that slow cooling rate was helpful to decrease slurry temperature gradient. The temperature difference between slurry centre and edge decreased from 8.3 to 4.1 degrees C when the cooling rate decreased from 1.63 to 0.69 degrees C/min. But low cooling rate also resulted in coarser grain. Grain morphology and size was modified by grain refiner. Trace amount of Al-5Ti-1B changed the grain morphology and size greatly, and improved the homogeneity of slurry microstructure. When the content of Ti increased from 0, 0.01 to 0.12%, the grain size was decreased from about 800 to 115 and 75 mu m respectively. These results suggested that low cooling rate and grain refiner were necessary for making Al-4.8Zn-1Mg semisolid slurry.