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研究了定向凝固时冷却条件和镁元素对Ａｌ－Ｓｉ１１．０合金树枝晶结构和共晶组织的影响。试验结果表明，随着冷却速度的增加，Ａｌ－Ｓｉ１１．０合金的一次枝晶和二次分枝间距都显著减小；在较小的冷却速度时，加入镁元素后合金的二次分枝间距明显增大，而在冷却速度大于１６０Ｋ／ｍｉｎ时，则没有影响。试验还发现，加入镁元素后，冷却速度对共晶成分的影响显著减小。提高冷却速度使得合金的共晶组织变细。在试验范围内，Ａｌ－Ｓｉ１１．０合金中加入０．１５％镁时，共晶组织变得较粗；而当镁的加入量增加到０．３％时，其共晶组织比Ａｌ－Ｓｉ１１．０合金细得多，分析了出现这一结果的原因。
The effects of cooling conditions and magnesium on dendritic structure and eutectic structure of Al-Si11.0 alloy were investigated. The experimental results show that the primary dendrite and secondary branch spacing of Al-Si11.0 alloy decreases with the increase of cooling rate. At the lower cooling rate, secondary branching of the alloy after addition of magnesium Pitch significantly increased, while the cooling rate is greater than 160K / min, it has no effect. The test also found that the addition of magnesium, the cooling rate of eutectic composition significantly reduced. Increasing the cooling rate causes the alloy’s eutectic structure to become thinner. In the experimental range, the eutectic microstructure becomes coarse when 0.15% magnesium is added into the Al-Si11.0 alloy, whereas the eutectic microstructure becomes larger than that of the Al-Si11 alloy when the addition amount of magnesium increases to 0.3% .0 alloy much thinner, analyzed the reasons for this result.