Al-Bi偏晶点成分合金定向凝固过程研究  

DIRECTIONAL SOLIDIFICATION OF MONOTECTIC COMPOSITION Al-Bi ALLOY

作　　者：杨志增[1] 孙倩[1] 赵九洲[1] 

机构地区：[1]中国科学院金属研究所

出　　处：《金属学报》2014年第1期25-31,共7页Acta Metallurgica Sinica

基　　金：国家自然科学基金项目51071159;51271185和51031003;中国载人航天工程项目资助~~

摘　　要：对Al-Bi偏晶点成分合金(Al-3.4%Bi,质量分数)开展了逆重力方向的定向凝固实验,考察了凝固速度对合金凝固组织的影响,分析了试样凝固组织形成过程.结果表明:Al-Bi偏晶点成分合金定向凝固时在固-液界面前沿液相内形成溶质Bi富集层,并发生液-液相变,少量相液滴在Marangoni迁移、Stokes沉积和试样自身下拉运动共同作用下进行空间迁移,当凝固速度较快时,凝固界面前沿所有尺寸的少量相液滴均向凝固界面迁移,合金凝固后少量相粒子尺寸呈现单峰分布;当试样凝固速度较慢时,部分少量相液滴在长大过程中其合速度方向按:指向凝固界面-背离凝固界面-再指向凝固界面顺序随液滴尺寸变化,合金凝固后少量相粒子尺寸分布呈现2个峰;当凝固速度较快时,少量相粒子平均尺寸<R>随凝固速度V_0近似呈<R>∝V_0^(-1/2)指数关系变化,随着凝固速度的下降,<R>与V_0间的关系向<R>∝V_0^(-1/3)指数关系趋近.Monotectic systems are a kind of extensive alloys. Many of them have great potentials for practical industry application. A lot of work has been carried out to study the solidification of monotectic alloys. But most of them focused on the microstructure formation during cooling a hyper-monotectic alloy through the miscibility gap in the liquid. Little work was done on the solidification behaviors of an alloy of monotectic composition. Directional solidification experiments were carried out with A1-Bi alloy of the monotectic composition （A1-3.4%Bi, mass fraction）. The influences of the solidification velocity on the microstructure were investigated. The microstructure evolution during solidification was analyzed. The results indicate that a solute-rich layer forms in front of the solidification interface and the liquid-liquid decomposition occurs there. When the alloy is solidified at such a high velocity so that the minority phase droplets of all sizes in front of the solidification interface are migrating to the solidification interface, the size distribution of the minority phase particles shows only one peak. When the alloy is solidified at a relatively low velocity, the minority phase droplets within a certain size range may move away from the solidification interface under the concurrent actions of the Marangoni migration, Stokes motion of the droplets as well as the movement of the sample. A1-3.4%Bi alloy solidified under such conditions shows a size distribution of the minority phase particles with two peaks. The average radius of the minority phase particles 〈R〉 depends on the solidification velocity V0 exponentially according to 〈R 〉∝V0-1/2 With the decrease of the solidification velocity, the dependence of the average radius of the minority phase particles varies towards to 〈 R 〉∝V0-1/3.

关 键 词：偏晶点成分合金 难混溶合金 定向凝固 

分 类 号：TG113.12[金属学及工艺—物理冶金]