定向凝固Al-4%Cu合金微观组织和溶质浓度影响因素研究

Study on Factors Influencing Structure and Solute Concentration in Directionally Solidified Al-4%Cu Alloy

以Al-4%Cu亚共晶合金为研究对象,研究不同试样尺寸、初始变形量以及晶体取向条件下定向凝固单晶Al-4%Cu合金微观组织、固溶体中溶质浓度变化,以及凝固过程中溶质的分布规律和影响因素。结果表明,随着试样直径增大,Al-4%Cu合金内非平衡共晶相体积分数提高,Cu溶质成分曲线越平缓,α-Al固溶体Cu溶质分布更加均匀,晶内偏析减小,这主要是由于大尺寸试样熔体中自然对流更加充分,促进了溶质在液相中的扩散,减轻了固液界面前沿溶质的富集;施加一定塑性变形后,由于变形导致试样中位错密度增加,位错增殖和运动过程中形成的空位缺陷可以容纳更多溶质原子,因而凝固初期Cu成分曲线升高,α-Al固溶体中溶质浓度增大;对于不同取向的试样,随着晶体取向偏离[001]方向角度增大,微观偏析先降低后增大,而固溶体中溶质浓度先增大后降低。这是由于固/液界面能存在各项异性,溶质原子进入固/液界面的难易程度与晶体取向相关,不同晶面原子的吸附能力不一致,从而导致固液界面前沿溶质富集和固溶体中溶质浓度存在差异。

Taking Al-4% Cu hypoeutectic alloy as the research object,the microstructure,changes of solute concentration in solid solution,solute distribution and influencing factors of the directionally solidified single crystal Al-4% Cu alloy with different sample sizes,initial deformation and crystal orientation were studied.The results show that with the increase of the sample diameter,the volume fraction of non-equilibrium eutectic phase in Al-4% Cu alloy increases,the composition curve of Cu solute becomes more gentle,the distribution of Cu solute in α-Al solid solution solute becomes more uniform,and the ingrain segregation decreases,which is mainly due to the more sufficient natural convection in the melt of the large sample,promoting the diffusion of solute in the liquid phase.The solute enrichment at solid-liquid interface was reduced.After a certain plastic deformation,the dislocation density in the sample increases.The vacancy defects formed during dislocation proliferation and movement can accommodate more solute atoms.As a result,the Cu composition curve increases and solute concentration increases in α-Al solid solution at the initial solidification stage.For samples with different orientations,as the angle of crystal orientation deviating from[001]direction increases,the microscopic segregation first decreases and then increases,while the solute concentration in the solid solution first increases and then decreases.This is because of the anisotropy of the solute atom at the solid-liquid interface.The difficulty of solute atom entering the solid-liquid interface is related to the crystal orientation,and the adsorption capacity of atoms on different crystal planes is inconsistent,which leads to the solute enrichment at the front of the solid-liquid interface and the difference of solute concentration in the solid solution.