The relevance of forced melt flow to grain refinement in pure aluminum under a low-frequency alternating current pulse

Abstract

Abstract

Research on Grain Refinement in Hypoeutectic Al-Si Alloy during Solidification under an Alternating Electric Current Pulse

“…This device provided the frequency from 2-1600 Hz and the current amplitude from 0-10,000 A. Since our previous studies [22] demonstrated that effect of current effects such as Joule heating, melt flow arising from Lorentz force on grain refinement could be insignificant when the AECP with 990 A was applied, the lower effective value of current amplitude is required to clarify the role of ∆G e . In our study, the selected effective values of current amplitude were 0, 300, 400 and 600 A, respectively.…”

“…Based on the improved experiments, Zhang et al [21] additionally indicated that the forced melt flow promoted dendrite fragmentation rates. From experimental investigation of the relevance of forced melt flow to the solidification structure of pure Al in the mold for embedding the wire mesh under an alternating electric current pulse (AECP) with up-down electrodes, our prior work [22] concluded that melt flow could lead to the columnar fragmentation and make the crystal nuclei on the mold wall fall off and drift in the liquid. Furthermore, Zhang et al [23] pointed out that the columnar fragmentation resulted from a solutal remelting of dendrite side arms in pure Al with a low purity grade due to the remarkable melt flow.…”

“…In the present work, the experimental investigation of the effect of a low AECP on the directionally solidified macrostructure of Al-7 wt.% Si alloy was carried out. As indicated above, electromagnetically driven convection plays an important role in grain refinement of solidified alloys [20,22,23]. In order to clarify the role of other current effects on grain refinement, a low enough AECP was selected to lead to a weak forced melt flow which hardly affected the solidification structure of alloys.…”

Effect of Direct Current on Solid-Liquid Interfacial Tension and Wetting Behavior of Ga–In–Sn Alloy Melt on Cu Substrate

“…To date, the main reasonable hypotheses proposed to explain the modification of the solidification structure are the increase in the solid-liquid interfacial tension [8], the reduction in the nucleation activation energy [9], the suppression of grain growth due to Joule heating [10], current crowding due to the differing electrical conductivities of solid and liquid [11], electromigration [12], and melt flow caused by Lorentz force [13], but all these taken together do not provide a consistent picture of the solidification structure evolution under electric current. This is mainly due to the lack of conclusive evidence provided by theoretical and experimental studies in support of the proposed hypotheses, especially in the solid-liquid interfacial tension and its related wettability of solid phase by liquid phase which play an important role in determining the kinetics of crystal nucleation and growth [14].…”

Three orthogonal ultrasounds fabricate uniform ternary Al-Sn-Cu immiscible alloy

“…It is well known that applying external physical fields is an effective way to control alloy solidification process12131415, among which the power ultrasound is proved to refine the grain size and promote the mechanical properties1617181920. The most popular way for introducing ultrasound is to insert a vibrating ultrasonic horn into the solidifying liquid alloys.…”