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

作     者：Nagasivamuni Balasubramani Gui Wang David H.St John Matthew S.Dargusch Nagasivamuni Balasubramani;Gui Wang;David H.StJohn;Matthew S.Dargusch

作者机构：Centre for Advanced Materials Processing and Manufacturing(AMPAM)School of Mechanical and Mining EngineeringUniversity of QueenslandSt Lucia 

出 版 物：《Journal of Materials Science & Technology》 (材料科学技术（英文版）)

年 卷 期：2021年第65卷第6期

页      面：38-53页

核心收录：

学科分类：080503[工学-材料加工工程] 08[工学] 0805[工学-材料科学与工程（可授工学、理学学位）] 0802[工学-机械工程] 080201[工学-机械制造及其自动化] 

基　　金：funding support provided by the Australian Research Council Research Hub for Advanced Manufacturing of Medical Devices IH150100024 the ARC Discovery grant DP140100702 ARC linkage project LP150100950 

主　　题：Ultrasonic treatment Grain refinement Equiaxed grains Magnesium Zinc Solidification 

摘      要：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.