Numerical Study on the Impact of Cooling Rate on the Solidification of Al-Bi Hypermonotectic Alloys

Abstract

A numerical model describing the liquid-liquid phase transformation of the nucleation, the diffusional growth, Ostwald coarsening and macro-transport phenomena was established based on Euler-Euler method. The microstructure development of Al-Bi alloys in different solidification rate has been simulated by coupling the calculated temperature and velocity fields with the kinetic equation which controls the microstructure evolution. The results showed that average diameter difference of L2 phase droplets between top and bottom of samples in low cooling rate increased by 151 % than in high cooling speed and the maximum volume fraction of the droplets at the bottom of the sample in low cooling rate much higher than in high cooling rate. Analysis that the bigger cooling rate can shorten the action time which caused by gravity settling and collisions coagulation of the droplets, and then improves the macrosegregation of solidification structure in favor of uniform distribution of the solidification structure.