Al-Pb偏晶合金连续凝固过程模拟

来源期刊：金属学报2010年第6期

论文作者：李海丽 赵九洲

文章页码：695 - 700

关键词：偏晶合金； 液-液相变； 凝固； 模拟

Key words：monotectic alloy； liquid-liquid transformation； solidification； modeling and simulation

摘    要：建立了偏晶合金连续凝固过程的群体动力学模型,并将其与传热、传质和流场控制方程相耦合,对Al-Pb偏晶合金连续凝固过程进行了模拟,分析了凝固速率、合金成分和熔炼温度等对合金连续凝固组织形成过程的影响.结果表明:凝固速率越大,凝固界面前沿弥散相液滴的形核位置越靠近凝固界面,弥散相液滴的形核率和数量密度越大,平均半径越小.越有利于获得弥散凝固组织;合金Pb含量越高,凝固界面前沿弥散相液滴的形核位置越远离凝固界面,弥散相液滴的形核率越低,平均半径越大,越不利于获得弥散凝固组织.熔炼温度越高,弥散相液滴的数量密度越大,平均半径越小,有利于获得弥散组织;但随熔炼温度提高,液滴的综合运动速度逐渐降低,该速度降为负值时,合金不能实现稳态凝固,导致偏析组织的形成.

Abstract: When a single-phase liquid is cooled into the miscibility gap,it decomposes into two liquid phases.Generally the liquid-liquid phase transformation causes the formation of a solidification microstructure with serious phase segregation.Many efforts have been made to use the liquid-liquid demixing phenomenon for the production of the finely dispersed metal-metal composite materials. It is demonstrated that the only effective method of preventing the formation of the microstructure with heavy phase segregation in monotectic alloys is using the rapid solidification processing techniques. Strip casting may have great potentials in the manufacturing of the bulk materials of this kind of alloys. In this paper,a model was developed to describe the microstructure formation in a strip cast monotectic alloy based on the population dynamic method.The model takes into account the concurrent actions of the nucleation,diffusional growth and motions of the minority phase droplets.The model was numerically solved together with the controlling equations for the heat transfer,mass transport and momentum transfer to study the microstructure development in the strip cast Al-Pb alloys.The effects of alloy composition,solidification velocity and melting temperature on the microstructure formation were investigated.The results indicate that with the increase of the solidification velocity, the nucleation position of the minority phase droplets moves towards the solidification interface,the nucleation rate and number density of droplets increase and the average droplet size decreases.All these are favorable for the formation of a well dispersed microstructure.With the increase of the Pb content,the nucleation position of the minority phase droplets moves away form the solidification interface,the nucleation rate decreases,and the average droplet size increases.These are against the formation of a well dispersed microstructure.With the increase of the melting temperature, the nucleation rate and number density of droplets increase and the average droplet size decreases. These are favorable for the formation of a well dispersed microstructure.But the velocity of the minority phase droplets decreases with the increase of the melting temperature.When the velocity of droplets is negative,samples can not obtain steady state solidification and result in the formation of a microstructure with massive segregation.