Unidirectional solidification of Sn- Pb alloys under forced melt flow

• Published in: IOP conference series. Materials Science and Engineering 2012-01, Vol.27 (1), p.012041-6
• Main Authors: Kovacs, J, Rogozsan, B, Ronafoldi, A, Roosz, A
• Format: Article
• Language: English
• Subjects: Alloys; Dendritic structure; Electromagnetic fields; Electromagnetic induction; Fluid dynamics; Fluid flow; Lead; Macrostructure; Magnetic fields; Magnetic induction; Melts; Microstructure; Rotating; Rotation; Solidification; Tin; Tin base alloys
• ISSN: 1757-899X; 1757-8981; 1757-899X
• DOI: 10.1088/1757-899X/27/1/012041

Cylindrical Sn-Pb alloy samples of different compositions (10, 20 and 30 wt.-% Pb) were prepared from high purity (4N) components. After metals have been melted, a rotating magnetic field (RMF) with an induction of 150 mT and a frequency of 50 Hz was switched on in order to homogenize the liquid. The electromagnetic field was generated by a 3-phase, 2-pole inductor. Just before the start of the solidification process, the magnetic field was switched off to achieve a microstructure free of melt flow influence. The sample translation velocity was constant (0.05 mm/s), and the temperature gradient changed from 7 to 3 K/mm during the solidification process. The first half part of each sample solidified without influence of rotating magnetic field while solidification of the second half part proceeded under the action of the RMF. The columnar microstructure formed in the absence of RMF induced fluid flow was replaced after switching on the RMF by a characteristic "Christmas tree"- like macro-segregated structure with equiaxed dendrites. The secondary dendrite arm spacing and the volume fraction of primary tin phase (dendrite) were measured by an automatic image analyzer on the longitudinal polished sections along the whole length of the samples. The effect of the forced melt flow and alloy composition on its micro- and macrostructure development was investigated.