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Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy.

Wang J, Yue S, Fautrelle Y, Lee PD, Li X, Zhong Y, Ren Z - Sci Rep (2016)

Bottom Line: Understanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites.With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found.To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200072, China.

ABSTRACT
Understanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.%Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope.

No MeSH data available.


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(a) Al2Cu column obtained without magnetic field; (b) x component magnitude of computed thermoelectric magnetic forces (TEMF) in Al2Cu column; (c) y component magnitude of computed TEMF in Al2Cu column; (d) and (e) Longitudinal and transverse structure of Al–40 wt.%Cu alloys obtained without and with magnetic field at growth rate of 2 μm/s; (f) Distribution of computed total stress in a transverse (x−y) plane at the column top. (For both experiment and simulation, B = 12T and G = 6000 K/m, the unit of colour legend is N/m3).
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f3: (a) Al2Cu column obtained without magnetic field; (b) x component magnitude of computed thermoelectric magnetic forces (TEMF) in Al2Cu column; (c) y component magnitude of computed TEMF in Al2Cu column; (d) and (e) Longitudinal and transverse structure of Al–40 wt.%Cu alloys obtained without and with magnetic field at growth rate of 2 μm/s; (f) Distribution of computed total stress in a transverse (x−y) plane at the column top. (For both experiment and simulation, B = 12T and G = 6000 K/m, the unit of colour legend is N/m3).

Mentions: The refinement of Al2Cu column may attribute to its fragmentation21 caused by the TEMF because the present solidification conditions permit the interaction between thermoelectric currents and magnetic field. The thermal gradient along solid-liquid interface together with the dissimilar thermo-physical properties (e.g. thermoelectric power) between solid and the melt give rise to the occurring of Seebeck effect, which results in thermoelectric currents flowing through both solid and melt25. To confirm this and understand how TEMF fragment the Al2Cu column, a 3D simulation of TEMF was performed based on the real Al2Cu structure that got from the tomography data and shown in Fig. 3(a). The detailed description of simulation method can be found in ref. 26 and the related physical parameters of Al2Cu and the melt are listed in Table 1. The temperature field, electric current density and fluid flow field was coupled to simulate TEMF using a finite element method based commercial code COMSOL Multiphysics. Figure 3(b,c) respectively shows the x and y component magnitude of the computed TEMF in Al2Cu column under a 12T axial magnetic field. It can find that TEMF orientate anticlockwise at the top (hot region) and clockwise at the bottom (cool region), so that a torque as indicated by the black arrows in Fig. 3(a) forms on the column. As the Al2Cu always grows ahead the eutectic front, the excess part of Al2Cu column could be fractured by this torque. Considering so, the discontinuous growth of Al2Cu column in axial direction could form under magnetic field, and this is just the case indicated by Fig. 3(d) that the longitudinal structure of Al-40 wt.%Cu alloys fabricated without and with a 12T magnetic field. In fact, as reflected by Fig. 3(e), the decrease transverse section area of each column can be interpreted by the TEMF as well. Figure 3(f) is the distribution of computed total stress in Al2Cu column in a transverse (x−y) plane at the column top. Subjecting to such stresses this column should tend to rotate, as mentioned above this column may contact with another one at any point around its edge during the rotation. Assuming this column contacts with and is blocked by the other one at the point marked by the black circle, it would not be difficult to image that the upper left part of this column would depart away under the stresses orienting towards to negative x axis. It is worthy to point out that the transverse section area of each Al2Cu column decrease gradually with magnetic fields is because the TEMF is linearly proportional to the applied magnetic field flux intensity21.


Refinement and growth enhancement of Al2Cu phase during magnetic field assisting directional solidification of hypereutectic Al-Cu alloy.

Wang J, Yue S, Fautrelle Y, Lee PD, Li X, Zhong Y, Ren Z - Sci Rep (2016)

(a) Al2Cu column obtained without magnetic field; (b) x component magnitude of computed thermoelectric magnetic forces (TEMF) in Al2Cu column; (c) y component magnitude of computed TEMF in Al2Cu column; (d) and (e) Longitudinal and transverse structure of Al–40 wt.%Cu alloys obtained without and with magnetic field at growth rate of 2 μm/s; (f) Distribution of computed total stress in a transverse (x−y) plane at the column top. (For both experiment and simulation, B = 12T and G = 6000 K/m, the unit of colour legend is N/m3).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4835779&req=5

f3: (a) Al2Cu column obtained without magnetic field; (b) x component magnitude of computed thermoelectric magnetic forces (TEMF) in Al2Cu column; (c) y component magnitude of computed TEMF in Al2Cu column; (d) and (e) Longitudinal and transverse structure of Al–40 wt.%Cu alloys obtained without and with magnetic field at growth rate of 2 μm/s; (f) Distribution of computed total stress in a transverse (x−y) plane at the column top. (For both experiment and simulation, B = 12T and G = 6000 K/m, the unit of colour legend is N/m3).
Mentions: The refinement of Al2Cu column may attribute to its fragmentation21 caused by the TEMF because the present solidification conditions permit the interaction between thermoelectric currents and magnetic field. The thermal gradient along solid-liquid interface together with the dissimilar thermo-physical properties (e.g. thermoelectric power) between solid and the melt give rise to the occurring of Seebeck effect, which results in thermoelectric currents flowing through both solid and melt25. To confirm this and understand how TEMF fragment the Al2Cu column, a 3D simulation of TEMF was performed based on the real Al2Cu structure that got from the tomography data and shown in Fig. 3(a). The detailed description of simulation method can be found in ref. 26 and the related physical parameters of Al2Cu and the melt are listed in Table 1. The temperature field, electric current density and fluid flow field was coupled to simulate TEMF using a finite element method based commercial code COMSOL Multiphysics. Figure 3(b,c) respectively shows the x and y component magnitude of the computed TEMF in Al2Cu column under a 12T axial magnetic field. It can find that TEMF orientate anticlockwise at the top (hot region) and clockwise at the bottom (cool region), so that a torque as indicated by the black arrows in Fig. 3(a) forms on the column. As the Al2Cu always grows ahead the eutectic front, the excess part of Al2Cu column could be fractured by this torque. Considering so, the discontinuous growth of Al2Cu column in axial direction could form under magnetic field, and this is just the case indicated by Fig. 3(d) that the longitudinal structure of Al-40 wt.%Cu alloys fabricated without and with a 12T magnetic field. In fact, as reflected by Fig. 3(e), the decrease transverse section area of each column can be interpreted by the TEMF as well. Figure 3(f) is the distribution of computed total stress in Al2Cu column in a transverse (x−y) plane at the column top. Subjecting to such stresses this column should tend to rotate, as mentioned above this column may contact with another one at any point around its edge during the rotation. Assuming this column contacts with and is blocked by the other one at the point marked by the black circle, it would not be difficult to image that the upper left part of this column would depart away under the stresses orienting towards to negative x axis. It is worthy to point out that the transverse section area of each Al2Cu column decrease gradually with magnetic fields is because the TEMF is linearly proportional to the applied magnetic field flux intensity21.

Bottom Line: Understanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites.With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found.To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Advanced Special Steel, Shanghai University, Shanghai 200072, China.

ABSTRACT
Understanding how the magnetic fields affect the formation of reinforced phase during solidification is crucial to tailor the structure and therefor the performance of metal matrix in situ composites. In this study, a hypereutectic Al-40 wt.%Cu alloy has been directionally solidified under various axial magnetic fields and the morphology of Al2Cu phase was quantified in 3D by means of high resolution synchrotron X-ray tomography. With rising magnetic fields, both increase of Al2Cu phase's total volume and decrease of each column's transverse section area were found. These results respectively indicate the growth enhancement and refinement of the primary Al2Cu phase in the magnetic field assisting directional solidification. The thermoelectric magnetic forces (TEMF) causing torque and dislocation multiplication in the faceted primary phases were thought dedicate to respectively the refinement and growth enhancement. To verify this, a real structure based 3D simulation of TEMF in Al2Cu column was carried out, and the dislocations in the Al2Cu phase obtained without and with a 10T high magnetic field were analysed by the transmission electron microscope.

No MeSH data available.


Related in: MedlinePlus