The Role of Electric Current-Associated Free Energy and Forced Convection on Grain Refinement in Pure Aluminum under Electropulsing

Ning Li,Limin Zhang,Rong Zhang,Kaikai Song,Hongjing Wu,Hui Xing,Pengfei Yin

doi:10.3390/ma12233846

Abstract

An experimental study with respect to the effect of an alternating electropulsing on grain refinement in pure aluminum was reported. The macrostructural observation with the mold preheated to different temperature and embedded the metal mesh indicated that the change of electric current-associated free energy related with the position of crystal nuclei (ΔGem) and forced convection dominated the generation of fine equiaxed grains (FEG). Under electropulsing with 480 A, ΔGem induced the dissociation of crystal nuclei from the upper interface of the electrode and the melt, leading to the generation of FEG. For a larger current intensity, FEG originated from the dissociation of crystal nuclei on the side wall besides the upper interface due to ΔGem and the forced convection. Furthermore, the model coupling the dissociation of crystal nuclei and dendrite fragmentation due to the forced convection and the dissociation of crystal nuclei due to ΔGem was presented to explain the formation mechanism of FEG in pure aluminum under electropulsing.

Highlights

It is well known that replacing the large grains in castings by the fine equiaxed grains (FEG)can significantly enhance the mechanical properties of cast alloys
With regard to the complicated mechanism of grain refinement with electropulsing, we suggest that the dissociation of heterogeneous nuclei driven by ∆Ge and forced convection are two important factors, and it has important fundamental significance for the development of this technique in practice
The effect of an alternating electropulsing on grain refinement in pure

Summary

Introduction

It is well known that replacing the large grains in castings by the fine equiaxed grains (FEG). Can significantly enhance the mechanical properties of cast alloys. Electromagnetic field [13,14,15,16], have been successfully applied during solidification process of alloys for the improvement of the solidification structure. The application of electropulsing during solidification, as a promising technique for achieving fine grains, has attracted considerable attention. Extensive experimental and theoretical studies have been performed to explain the formation mechanism of FEG with electropulsing treatment [17,18,19]. It is generally accepted that FEG is mainly achieved during the nucleation stage [3]

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Conclusion