Effect of cooling rate on morphology of primary particles in Al-Sc-Zr master alloy

Al-1.0%Sc-1.0%Zr (mass fraction) master alloy was prepared at different cooling rates. The morphology and thermodynamics data of the primary particles of the master alloy were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). It shows that the primary particles are dendrite-shaped particles comprised of several attached small cubic, cusped-cubic or crucifer shape particles at slow cooling rate. However, the primary particles are separated with crucifer shape at intermediate cooling rate, and they are cubic with cusped-cubic shape at high cooling rate. Meanwhile, the separated and attached particles present Al3Sc/Al3Zr1-xScx core-shell structure. The formation mechanism of the structure was systematically investigated by a mathematical model.