电磁搅拌对过共晶Al—Si合金初生Si分布的影响

系统研究了电磁搅拌下过共晶Al-Si合金初生Si的偏析规律，实验表明，虽然电磁搅拌引起过共晶Al-Si合金中初生Si的显著细化和圆整化，但常会使坯料表面出现初生Si偏析层，合金中Si含量越大，初生Si偏析层越厚，提高电磁摘抄功率、降低合金熔体冷却速率都会减小或消除初生Si偏析层；在电磁摘抄条件下，坯料表面产生初生Si偏析层的主要原因是固－液界面处的温度梯度过大和存在一层流附面层。

EFFECT OF ELECTROMAGNETIC STIRRING ON THE DISTRIBUTION OF PRIMARY SILICON IN HYPEREUTECTIC Al-Si ALLOYS

The segregation of primary silicon crystals in solidifying hypereutectic Al-Si alloys stirred by electromagnetic field has been studied systematically. The primary silicon segregation layer often exists near by the billet inner surface, although electromagnetic stirring can fine primary silicon crystals and modify their shape, and the more the amount of silicon content in alloys, the thicker the segregation layer. If the electromagnetic stirring power is increased and the cooling rate of the melt is decreased, the primary silicon segregation layer can become thinner or disappear. The main reasons about emergence of the primary silicon segregation layer is that the temperature gradient between the liquid and solid surface is too large and a lamellar flow area exists near the mould wall.