实验研究了微量元素Bi对Al-Pb合金凝固过程和显微组织的影响, 发现微量元素Bi能显著细化Al-Pb合金凝固组织中的富Pb相粒子, 细化效果随着Al-Pb合金Pb含量的增加而增强. 分析了微量元素Bi对Al-Pb合金液-液相变过程的影响机理, 模拟计算了微量元素Bi作用下Al-Pb合金凝固组织形成过程. 结果表明, 微量元素Bi减小Al-Pb合金液-液相变过程中液相间的界面能, 提升了富Pb相液滴的形核率, 促进富Pb相液滴的细化和Al-Pb合金弥散型凝固组织的形成.

Monotectic alloys are characterized by a miscibility gap in the liquid state. Many of them have great potentials to be used in industry. For example, alloys based on Cu-Pb and Al-Pb are good candidates to be used as advanced bearing materials if the soft Pb phase is dispersed in the Al or Cu matrix. Cu-Cr alloy is a high-strength, high conductivity material and Cu-Co alloy is an excellent magneto-resistive material, etc.. However, when a homogeneous monotectic alloy melt is cooled into the miscibility gap, it will transform into two liquids. The liquid-liquid decomposition generally causes the formation of a phase segregated microstructure. In recent years, considerable efforts have been made to investigate the solidification behavior of monotectic alloys. A lot of experiments have been carried out under microgravity conditions in space as well as under the gravitational conditions on the earth. The solidification behaviors of monotectic alloys under the conventional and rapid solidification conditions as well as the effect of external fields, such as electric current, magnetic field etc., are investigated. Models describing the solidification process have been built and the microstructure formations under different conditions have been calculated. It has been demonstrated that the microstructure evolution during cooling an alloy in the miscibility gap is a result of the concurrent actions of the nucleation, growth, Ostwald ripening and motions of the dispersed phase droplets. The nucleation of the dispersed phase droplets has a dominant influence on the solidification microstructure of monotectic alloys. In this work, solidification experiments were carried out to investigate the effect of micro-alloying element Bi on the solidification of Al-Pb alloys. The experimental results demonstrate that micro-alloying element Bi can cause an obvious refinement of the Pb-rich particles. The refining effect increases with the increase of the Pb content of Al-Pb alloys. The affecting mechanism of micro-alloying element Bi on the solidification process of Al-Pb alloys was analyzed. The microstructure formation process was calculated. The numerical results indicate that the addition of micro-alloying element Bi causes a reduction in the interfacial energy between the two liquid phases and, thus, enhances the nucleation rate of the Pb-rich droplets and promotes the formation of Al-Pb alloys with a well-dispersed microstructure.