Effect of High Rotating Magnetic Field on the Solidified Structure of Al–7wt.%Si–1wt.%Fe Alloy

Abstract

Al–7wt.-% Si–1wt.-% Fe alloy was solidified unidirectionally in the Crystallizer with High Rotating Magnetic Field (CHRMF). The diameter of sample was 8 mm and its length was 120 mm. The parameters of solidification were as follows: solid/liquid interface velocity ~0.082 mm/s, temperature gradient 7+/-1 K/mm, magnetic induction 0 and 150 mT, frequency of magnetic field 0 and 50 Hz. The structure solidified without rotating magnetic field (RMF) showed a homogeneous, columnar dendritic one. The structure solidified by using magnetic stirring showed a dual periodicity. On the one hand, the branches of the “Christmas tree”-like structure known from the earlier experiments contained Al+Si binary eutectic. On the other hand, bands with higher Fe- and Si-content formed in the sample, which were at a larger distance from each other than the branches of the “Christmas tree” structure. The developed microstructure was analyzed by SEM with EDS. The average Si- and Fe-concentrations were measured on the longitudinal section at given places along the length of sample. Furthermore the Si- and the Fe-concentrations close to the bands and among the bands as well as the composition of the compound phases were determined.

Mushy Zone Morphology Calculation with Application of CALPHAD Technique

“…However, during solidification, the composition may change due to fluid flow evolution or due to the segregation in the remaining liquid. The earlier EDS measurements [29] for AlSi7Fe1.0 alloy on similar specimens (with 8 mm diameter and 120 mm long), showed almost constant Si and Fe concentration along samples solidified without melt stirring. However, for solidification with high rotating magnetic field (HRMF) of 150 mT and temperature gradient 7 K/mm, segregation was found to occur both along and across sample.…”

“…Such a composition shift would also result in a slightly wider liquid channel. Considering that the segregation measurements [29] by HRMF were made with 150 mT and current studies by RMF only 6 mT, it can be safely estimated that any change to the values presented here resulting from segregation along the sample length would be much less than a 10% reduction in mushy zone length and similarly scaled change to the liquid channel width.…”

Thermo-Calc Prediction of Mushy Zone in AlSiFeMn Alloys

“…However, fluid flow may change composition due to segregation. The almost constant chemical composition along sample length in similar studies [40] was presented for AlSi7Fe1.0 alloy (120 mm long and 8 mm diameter specimens) solidified directionally without stirring. The segregation was found both across and along the sample for experiments with temperature gradient 7 K/mm and high rotating magnetic field (HRMF) of 150 mT.…”

“…Such changes might move the composition on the Al-Si-Fe (Figure 3a) or on the Al-Si-Mn (Figure 3b) phase diagram (Figure 3) to the right, and the 7 • C decrease of liquidus and might cause dendrites to be about 2.3 mm shorter and the liquid channel to be slightly wider. Because solidification by HRMF [40] were carried out with 150 mT and current studies by RMF only 6 mT, it can be stated that results presented here would be much less than a 10% reduction, as an effect of segregation across the sample diameter.…”