Effect of frequency and intensity of rotating magnetic field on the microstructures of Pb-Sn alloys

• 来源期刊: 科学通报（英文版）
• 年，卷（期）: 2008,（17）
• 页码范围: 2575-2581
• 页数: 7页
• 语种: 英文
• DOI: 10.1007/s11434-008-0368-4

摘要

The solidification microstructures of Pb-45% Sn hypoeutectic and Pb-85%Sn hypereutectic alloys were studied in rotating magnetic field (RMF). A transition of primary phase from dendrite to spherical growth was caused by the RMF, which simultaneously fractured and fined grains. The fracture and re-finement increased first and then decreased with the increase in RMF intensity. When magnetic inten-sity exceeded a critical value, the size of the primary phase became bigger on the contrary. Therefore, there existed an optimum value of magnetic intensity in fracture and refinement of grain. Moreover, the rotating frequency determined the skin depth of magnetic field, and further affected the homogeniza-tion of temperature and solute. The rotating frequency and magnetic intensity were key factors affect-ing refinement and uniformity of solidification microstructures. The introduction of RMF not only changed the solidification thermodynamics, but also led to a reduction in Gibbs free energy associated with the formation of critical crystal nucleus and atom diffusion activation energy, thus enhancing the rate of nucleation.