Zr对Sr变质近共晶Al-Si铸造合金组织的影响

Sr作为变质剂加入到Al-Si合金中能导致共晶硅的形态从粗在的片状（或针状）转变为细小的纤维状,但同时也促进长柱状枝晶的形成。为了抑制长柱状枝晶的形成,本研究采用金相显微镜和扫描电镜分析Zr对Sr变质近共晶Al-Si铸造合金组织的影响。结果表明,随着Zr加入量的增加,枝晶α（Al）有等轴化趋势,长柱状枝晶的主干长度缩短,且对共晶硅的形态、尺寸没有明显影响,当Zr加入量为0.5～0.6%时,枝晶α完全等轴化。这是由于熔体中形成了ZrAl3颗粒,在合金凝固过程中,起到了异质生核作用。

Influence of Zr on the Microstructure of Near-Eutectic Al-Si Casting Alloys Modified with Sr

The addition of Sr in Al-Si alloys as a modifier can result in transition of eutectic silicon from coarse plate-like or acicular to fine fibrous. However, it may also lead to the formation of long columnar dendrite α phase. The influence of Zr on microstructure of near-eutectic Al-Si alloys was studied using optical microscopy and SEM. Tne result indicated that increasing of Zr addition, α dendrite tends to change from long colunmar to equiaxed, and there were no noticeable changes of the eutectic silicon.When adding 0.5% -0.6%Zr, the dendrite α phase was equiaxed fairly. This is because, during solidification, ZrAl3 particles were formed in the melt playing a role of hetergeneous nucleation.