Sr,B添加对Al-15.5%Si合金中共晶团尺寸的影响

EFFECTS OF ADDITION OF Sr AND B ON THE SIZE OF EUTECTIC CELLS IN Al-15.5%Si ALLOY

考察了Sr,B及Sr+B联合作用对Al-15.5%Si(质量分数)合金中共晶团尺寸大小的影响.实验结果表明,随合金中Sr量增加,共晶团尺寸呈减少的趋势,冷却速度对共晶团的影响也很显著;在Sr变质的合金中加入B,共晶团尺寸先显著下降,随B量增加降低幅度趋于平缓;在未变质的Al-15.5%Si合金中单独加B,共晶硅由粗大的片状变为细长的层片状,层片间距明显降低.分析认为,合金中加入Sr,导致共晶过冷度增大,因而共晶团形核驱动力增大促使共晶团细化;合金中加入B,增加了共晶团有效形核基底的数量促使共晶团显著细化.

Additions of Sr, B and combination of Sr and B in Al-l5.5%Si （mass fraction） alloy have obvious effects on the size of eutectic cells in the alloy. The size of eutectic cells decreases with increasing Sr content, and the cooling rate during solidification also has a considerable influence on it in the Sr-modified alloys. With increase in B amount in Sr-modified Al-15.5%Si alloy, the size of eutectic cells decreases sharply at first and tardily later. The addition of B in unmodified Al-15.5%Si alloy could result in a transition of the flake-like eutectic silicon from course to fine and the spacing between the silicon flakes also apparently decreased. The addition of Sr led to a depression of the eutectic temperature in Al-Si alloy, and hence, the nucleating driving force of the eutectic cells was increased, which resulted in the refinement of the eutectic cells. It was thought that the addition of B caused a considerable increase in the amount of the heterogeneously nucleated substrates of the eutectic cells in the melt.