Evolution of particle morphology in semisolid processing

Abstract

Experimental results are summarized of the formation of spheroidal grain structures in an Al-4.5 wt pct Cu alloy by (1) isothermally holding very fine equiaxed dendrites in the liquid-solid region and (2) direct spheroidal solidification from the melt. The fine-grained dendritic structure was obtained by very rapid solidification in a thin-section (0.8 mm) permanent-mold plate casting under conditions such that solidification took place during the filling process and, hence, during rapid fluid flow. Grains of approximately 30 m in diameter (representing a grain density of about 3 ϫ 10 4 mm Ϫ3 ) were obtained; these ripened to a spheroidal morphology in the liquid-solid region in less than 5 seconds. A similarly high grain count was then obtained in the bulk melt by vigorous agitation and rapid cooling near the liquidus temperature; the melt was thereafter cooled more slowly. Under these conditions, a spherical morphology formed early in solidification and grew in that form. The evolution of particle size with time in the liquid-solid region is shown to be essentially identical in the initially dendritic and spherical-growth experiments.

Puddling: A New Look at an Old Process

“…From this work it is known that vigorous stirring in the initial stages of solidification causes dendrites to "break up" into fine grains which then grow more-or-less spherically, their size depending only on ripening kinetics and hence on time in the liquid-solid zone. 11,12) Hence in our example of a 30 min boiling time with, say 20 min of that during the solidification stage, the average size of these spheroids would be about 60 microns.…”

Modélisation de l'écoulement de l'aluminium semi-solide dans le moulage sous pression /

“…Le procédé SEED, breveté par Alcan Inc., a été utilisé pour produire l'aluminium semi-solide. figure 1 : Limite élastique vs allongement à la rupture pour diverses méthodes de production, AlSi7Mg0.3 [8] 2-3 figure 2 : Schématisation de la fabrication de lopins de A1SS SEED [17] 2-6 figure 3 : Microstructure typique obtenue par SEED [17] 2-7 figure 4 : Schématisation du procédé du MIT [18] 2-8 figure 5 : Microstructure typique obtenue par MIT [13] 2-9 figure 6 : Schématisation du procédé UBE [19] 2-10 figure 7 : Microstructure typique obtenue par UBE [16] 2-10 figure 8 : Microstructure typique obtenue par MHD [16] 2-11 figure 9 : a) Remplissage partiel de A356 à 7.8 m/s, b) simulation correspondante [23] 2-12 figure 10 : a) Remplissage partiel de A356 à 2.0 m/s, b) simulation correspondante [23] 2-12 figure 11 : Seuil de cisaillement en fonction de la fraction solide pour l'alliage A356 [24] 2-13 figure 12 : Résultats expérimentaux utilisant divers fluides analogues (droite); et simulations correspondantes (gauche) [32] 2-15 figure 13 [40] 3-6 figure 20 : Thixotropie de A356, fs=0.30. Au temps 0, le taux de cisaillement est passé de A) 105 à 1.7 s-1 et B) 1.7 à 105 s-1 [41] 3-7 figure 21 : Viscosité de A356 tel qu'observée par différents expérimentateurs [20,22,40] 3-12 figure 22 : Fraction solide de l'AlSS en fonction de la température (Scheil) Plusieurs de ceux-ci étaient causés par la géométrie du moule et auraient dû être perçus lors des simulations numériques.…”

Secondary Solidification Behavior of A356 Aluminum Alloy Prepared by the Self-Inoculation Method

“…Therefore, the semisolid forming technology can obtain products without the hole-class defects in theory [3][4][5]. After half a century of exploration and research, domestic and foreign scholars have proposed the preparation process of forming semisolid slurry such as SSR (Semi-solid Rheocasting) [6], CRP (Continuous Rheoconversion Process) [7], NRC (New Rheocasting) [8], SEED (Swirled Enthalpy Equilibration device) [9], etc. Based on the characteristics of low superheat pouring, liquid-liquid mixed casting, solid-liquid mixed casting, suspension casting, and the inclined cooling method, a new type of solidification structure control method is proposed, which is called Self-inoculation Method (SIM) [10].…”