A356合金细化处理效果的孕育和衰退

通过考察A356合金在静置过程中细化效果的变化，研究了亚共晶铝硅合金细化处理的孕育期和衰退期。细化处理的孕育期的形成是由于细化初期的溶质过冷度小造成的，随着溶质Ti含量的增加，溶质过冷度增大，从而激活更多的形核质点，限制枝晶生长；长时间静置后，尽管细化元素Ti含量基本不变，但是成分偏析倾向加剧，形核质点粗化并沉淀，有效核心减少，出现细化效果衰退；采用预细化合金锭可以缩短甚至消除细化处理的孕育期。

Incubation and Fading of Refining Effects on Hypoeutectic Al-Si Alloy

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.