Structural and crystallographic study on 3004 aluminum alloy ingot by horizontal direct chill casting under combined ele
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fect of combined electromagnetic fields (EMFs) on the structures of a 3004 aluminum alloy ingot produced by horizontal direct chill casting was crystallographically investigated. The results showed that the structure was transformed from a mixture of equiaxed and fine columnar grains to coarse columnar grains with switching off the EMFs. With the EMFs the grain size is small and shows a uniform distribution, whereas without the EMFs it is increased and reveals inhomogeneous distribution on the cross section. Besides, a transition region composed of fine equiaxed grains appeared at the moment the EMFs were switched off (between the mixture and coarse columnar grains). Furthermore, the microstructure transformation is accompanied by a crystallographic orientation change from a preferred ,100. orientation to a random orientation, and then to an intense ,100. fiber texture. The structural and crystallographic transformations are mainly related to the forced convection in the melt due to the induced Lorentz force by the EMFs.
I. INTRODUCTION
Direct chill (DC) casting is a common process for industrial production of aluminum alloy billets and slabs. Just due to its importance for fabricating semifinished products, numerous studies have been carried out to develop this technique. Usually, DC casting process has two forms—vertical DC (VDC) and horizontal DC (HDC).1 Despite that VDC casting is the most preferred process used in industry at present, HDC process is attracting attention of aluminum industry in recent years.2 Compared to VDC, HDC has advantages of lower investment cost, higher flexibility, longer casting times, etc.3 Therefore, it is of practical significance to further develop HDC process. To improve the qualities of slabs and billets, many techniques referring to application of electromagnetic field (EMF) to the DC casting processes have been developed, such as electromagnetic casting (EMC),4,5 casting, refining, electromagnetic (CREM),6,7 and low frequency electromagnetic casting (LFEC).8–11 The EMC mainly aimed at improving surface quality of the ingots, whereas the CREM aimed at both surface quality and microstructure. For the LFEC, besides these advantages, it could also reduce macrosegregation and avoid hot tearing of large sized ingots. In these techniques, the EMF was usually applied individually. In reality, experiments of Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.29 J. Mater. Res., 2015
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combining the same or different EMFs and thus imposed to the DC casting processes were also conducted. A typical example was the electromagnetic vibration technique, in which alternating and direct current EMFs were applied simultaneously to the casting process of aluminum alloys.12 It was found that the microstructures became more homogeneous and refined than those with a single one. Other than this, combined out-phase EMFs were also imposed to the casting process of hollow aluminum
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