By observing the change of grain size of A356 alloy during holing

the incubation and fading of refinement on hypoeutectic Al-Si alloy were researched.Incubation of refinement is resulted from low solute supercooling degree during early stage of refinement.With the argument of the melt supercooling degree caused by solute Ti increase

more nucleated particles are activated to restrain the growth of dendrite.After long holding time

although the content of refining element Ti isn’t changed

refinement effect is fade due to the serious composition segregation and coarsing and disposition of nucleated particle resulting in the reduction of the active nucleation site.The incubation can be shortened or eliminated by using pre-refined alloy ingot.