Numerical Simulation Under Shear And Dynamics Study On Morphological Stabilities Of The Solid-liquid Interface Of Globular Particle

In semisolid metal processing, the interaction between melt flow and solidificationmicrostructure is one of the fundamental research fields in materials science. It plays animportant role in how to get the spherical semi-solid microstructure under certain conditionand technology. Recent study showed that globular crystals could form through directnucleation. However, to date, the formation mechanism of this kind of globular microstructurehas not yet been much studied.Based on the computational fluid dynamics theory and the forming mechanism ofsemi-solid organization, we studied the flow field of molten metal during shear by usingFLUENT software. It was concluded that, as rotation velocity increased, melt flow state wasdifferent from traditional simple laminar flow, and velocity changed dramatically along theaxial direction. At the same time, the fluid particle’s vector was not simply along thecircumferential direction, but tended to present ramified regular distribution between laminarflow and turbulent flow. Maximum vorticity mainly dispersed near the rotation cylinder wallon which particle possessed the largest value, and the phenomena was consistent with theexperimental result which was that the spherical particle firstly occurred around the rotationcylinder wall. It preliminarily accounted for why spherical particles directly occurred aroundthe rotation cylinder wall.Based on the effect of particle’s rotation movement, morphological stabilities of thespherical solid-liquid interface in supercooling melt in semisolid metal processing was furtherstudied in this article. Firstly, vorticity and shear rate value was obtained by numericalsimulation, then spherulite rotation angular velocity was derived from the above values. Thedynamics equation of spherical solid-liquid interface morphological stabilities under globularparticle rotation was first derived, and then the expression of criterion for sphericalsolid-liquid interface morphological stabilities was also defined, finally the crystal growth rateand crystal critical radius within which the spherical solid-liquid interface in supercoolingmelt was steady were obtained. The results showed that increasing the particle rotationangular rate and supercooling in melt can decreased the globular particle critical radius whichdecreased dramatically and then slowly. For SCN-5%water alloy and Sn-15%Pb alloy, theresults of the theoretically calculated analysis about the globular particle critical radius andparticle growth rate agreed approximately with the experimental results. The research revealedthe mechanism of spherical grains directly occuring in the melt under shear mixing, inaddition, it can instruct the preparation of semi-solid materials in a new way.