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A review of the origin of equiaxed grains during solidification under mechanical stirring,vibration,electromagnetic,electric-current,and ultrasonic treatments

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Journal of Materials Science & Technology 2023年第13期144卷 243-265页

作者： Nagasivamuni Balasubramani Jeffrey Venezuela David StJohn Gui Wang Matthew Dargusch Centre for Advanced Materials Processing and Manufacturing(AMPAM) School of Mechanical and Mining EngineeringUniversity of QueenslandSt.LuciaQLD 4072Australia

Refinement of grains and intermetallic phases in the as-solidified alloy structure offers uniform struc-tural properties,eliminates or minimizes common solidification defects,including segregation and hot cracking,and improves thermomechanical processing of wrought *** processing by an external field is an efficient process for achieving refinement of the solidification structure of Al and Mg alloys without altering the alloy composition.A wide range of melt processing methods and solidification stud-ies(conventional,directional,and in-situ approaches)have been reported in the literature that explore the mechanism of *** the dominant grain refinement mechanism has been a focus of most investigations because significant variations exist according to the casting conditions and the type of applied external *** origin of fine grains occurs through either one or a combination of heterogenous nucleation,fragmentation of dendrites and grains formed and then separated from the surface of the melt and mould wall under vibration or *** first part of this review describes the prominent external field techniques and the mechanisms proposed for the origin of fine *** second part critically compares the current understanding of these grain refinement mechanisms to de-termine differences and commonalities to identify the factors that promote the formation of equiaxed zones occupying a large volume fraction of the casting.

关键词： Grain refinement Solidification Melt processing equiaxed grains Intermetallic refinement

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Current understanding of the origin of equiaxed grains in pure metals during ultrasonic solidification and a comparison of grain formation processes with low frequency vibration,pulsed magnetic and electric-current pulse techniques

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Journal of Materials Science & Technology 2021年第6期65卷 38-53页

作者： Nagasivamuni Balasubramani Gui Wang David H.St John Matthew S.Dargusch Centre for Advanced Materials Processing and Manufacturing(AMPAM) School of Mechanical and Mining EngineeringUniversity of QueenslandSt Lucia

The formation of fine,non-dendritic equiaxed grains throughout a casting without the addition of refiners(*** of alloy chemistry),is made possible by using ultrasonic,magnetic or pulsed magnetic and electric current pulse *** dominant mechanisms proposed for the grain refinement produced during the application of an external field are cavitation phenomena assisted nucleation or fragmentation of dendrites(ultrasonic field),wall crystals arising from the cold surface of the mould(electric current pulse,magnetic and pulsed magnetic fields).In all these cases fluid flow provides an additional contribution(*** temperature gradients,growth rate and remelting of dendrites)to maintaining an equiaxed grain *** origin of equiaxed grains under an external field also depends on the casting conditions(volume and shape of casting)and the type of alloy other than the mechanisms specific to a particular *** current work aims to provide a detailed understanding of the various factors and mechanisms that influence the grain refinement achieved during the solidification of pure metals(magnesium and zinc)subjected to Ultra Sonic Treatment(UST).The role of the temperature range of UST application,time duration and an unpreheated sonotrode are examined with respect to the origin,evolution of equiaxed grain structure,morphology and the columnar to equiaxed *** origin of grains was analysed from three fundamental aspects that contribute to refinement(i)heterogeneous nucleation(ii)fragmentation of existing dendrites and(iii)grains produced from the colder surfaces(arising from mould walls or vibrating surfaces as wall crystals).A comparison of UST refinement with mechanical,low-frequency vibration,electric current pulse and magnetic field solidification of pure metals has also been provided to highlight the importance of the cold surfaces(sonotrode and mould wall)in influencing grain refinement.

关键词： Ultrasonic treatment Grain refinement equiaxed grains Magnesium Zinc Solidification

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Effect of low-frequency rotary electromagnetic-field on solidification structure of continuous casting austenitic stainless steel

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Journal of Central South University 2009年第3期16卷 360-364页

作者：周书才白晨光雷亚任正德曹鹏军杨治立 College of Material Science and Engineering Chongqing University College of Metallurgy and Material Engineering Chongqing University of Science and Technology

To understand the solidification behavior of austenitic stainless steel in rotary electromagnetic-field, the influence of low-frequency rotary electromagnetic-field on solidification structure of austenitic stainless steel in horizontal continuous casting was investigated based on industrial experiments. The results show that the solidification structure of austenitic stainless steel can be remarkably refined, the central porosity and shrinkage cavity can be remarkably decreased, and the equiaxed grains zone are enlarged by means of application of appropriate low-frequency electromagnetic-field parameters. The industrial trials verify that the stirring intensity of austenitic stainless steel should be higher compared with that of plain carbon steel. Electromagnetic stirring affects the macrostructure even if the average magnetic flux density of the electromagnetic stirring reaches 90 mT (amplitude reaches 141 mT) with the frequency of 3-4 Hz. Due to a higher viscosity, rotating speed of molten stainless steel is 20%-30% lower than that of molten carbon steel in the same magnetic flux density.

关键词： horizontal continuous casting austenitic stainless steel electromagnetic stirring equiaxed grains central porosity

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Effect of Longitudinal Magnetic Field on Microstructures of Directionally Solidified Ni-Based Superalloy

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Journal of Iron and Steel Research International 2012年第S1期19卷 390-393页

作者： XUAN Wei-dong REN Zhong-ming LI Chuan-jun School of Material Science and Engineering Shanghai University

The effect of a longitudinal static magnetic field on the microstructures of the superalloy DZ417G during directional solidification at the low withdrawal velocity was investigated *** experimental results showed that the application of a high static magnetic field significantly changed the interface shapes and microstructures of the *** practice,when the magnetic filed is applied,the well-ordered columnar dendrite structures still existed in the entire sample as the increase of magnetic field from 0 to 0.3 *** the increase of magnetic field,the columnar to equiaxed transition(CET)occurred and reaches a maximum under a 0.5 T magnetic filed,and then decrease with the magnetic filed still *** the magnetic field is higher than 1.2 T,equiaxed grains zone on the edge of sample increased again and gradually extended from the edge to the center of the ***,the macrosegregation may occur along with the appearance of the equiaxed *** phenomena should be contributed to interaction of the EMD and TEMC in liquid phase and TEMF in solid phase.

关键词： magnetic field directional solidification superalloy dendrite spacing equiaxed grains freckles

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