【作者】 唐玲；

【导师】 李双明；

【作者基本信息】 西北工业大学 ， 材料加工工程， 2007， 硕士

【摘要】 本文研究了Al-38.5％Cu过共晶合金在恒速和跃迁变速定向凝固下的组织演变，重点探讨了通过跃迁加速定向凝固过程来扩大共晶共生区的可行性，同时分析和研究了Al-38.5％Cu过共晶合金中Al₂Cu初生相的生长机理。 定向凝固恒速实验中，Al-38.5％Cu过共晶合金在250K／cm的温度梯度和凝固速度1μm／s下，获得的最终凝固组织为规则的层片共晶，与理论计算结果合金凝固速度低于3.55μm／s时可得到耦合生长的共晶组织相一致。实验中当定向凝固速度在5～490μm／s时，Al-38.5％Cu合金中Al₂Cu初生相领先于共晶组织生长，并随着凝固速度的提高，初生相的形态由工字形向圆弧花形转变。 考虑到恒速定向凝固下，Al-38.5％Cu过共晶合金中存在热溶质对流，结果合金凝固组织随凝固固相分数的增加由初生相+共晶组织向全耦合生长的共晶组织转变。采用Scheil方程分析和预测了该合余中不同凝固分数下的溶质分布，结果表明合金凝固速率在5μm／s和10μm／s下，凝固的固相分数分别大于0.62和0.7时，合金凝固组织就可转变为全耦合生长的共晶组织，而这与实验中凝固速率5μm／s和10μm／s时实测的固相分数大于0.49和0.66就可以得到全耦合生长的共晶组织相吻合。 通过跃迁加速定向凝固抑制了Al-38.5％Cu过共晶合金中0.Al₂Cu初生相的生长，使得在较高的凝固速度下仍然能获得耦合生长的共晶组织，这为提高共晶自生复合材料的生产效率和扩大共晶共生区提供了一个新的技术途径。 对比恒速和变速定向凝固下Al-38.5％Cu过共晶合金中层片问距的变化，可发现恒速定向凝固下，合金凝固组织中层片平均间距比跃迁变速定向凝固下相同速率获得的共晶层片间距要大，它们与JH模型的理论计算都比较接近。更多还原

【Abstract】 In this paper, directionally solidified microstructures of Al-38.5%Cu hypereutectic alloys were investigated both at constant growth rates and at the change growth rates. The solidification behaviors of Al-38.5%Cu hypereutectic alloys, including coupled growth zone and adjustment mechanisms of lamellar spacing of eutectic were researched by an abruptly changing growth rate in directional solidification. The formation mechanism of primary Al₂Cu phase and the effect of thermosolutal convection on directionally solidified microstructures of Al-Al₂Cu hypereutectic alloys were presented and discussed.At a given temperature gradient of 250K/cm and the growth rate of 1μm/s, coupled growth lamellar eutectic of Al-38.5%Cu alloy was obtained, which was in agreement with the theoretical analysis result that indicated the growth rate should be less than 3.55μm/s. As the growth rate ranged from 5μm/s to 490μm/s, the primary Al₂Cu phase grew ahead of the growth interface of coupled eutectic and its morphology was changed at various growth rates.Thermosolutal convection has a remarkable effect on the directionally solidified microstructures of Al-38.5%Cu hypereutectic alloys. The results show that with the increase of solid fraction, the quantity of primary Al₂Cu phase was decreased gradually. Using the Scheil equation to predict and analyze the solute segregation in the solidified sample both at V=5 and V=10μm/s, the coupled growth lamellar eutectic could be obtained at the solid fraction larger than 0.62 and 0.7 respectively, which fit in with the experimental results of 0.49 and 0.66 in directional solidification of Al-38.5%Cu hypereutectic alloy.When the growth rate increased abruptly, the growth of θ- Al₂Cu phase was suppressed in directionally solidified microstructures of Al-38.5%Cu hypereutectic alloy. The results show that at higher growth rate, the coupled growth eutectic can keep growth without any coarse primary phases that illustrates the production of in-situ composite improved effectively.The eutectic lamellar spacing of solidified microstructure in Al-38.5%Cu alloy was refined by the abrupt increases of the growth rate. Both at constant growth rates and the abrupt increase growth rates, the values of eutectic lamellar spacing are close to the JH model analysis results.更多还原