UNIVERSITY OF QUEBEC AT CHICOUTIMI DISSERTATION PRESENTED TO THE UNIVERSITY OF QUEBEC AT CHICOUTIMI IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN ENGINEERING BY OMID LASHKARI THE RHEOLOGICAL BEHAVIOR OF SEMI-SOLID A356 ALLOY JULY 2006 Mise en garde/Advice Afin de rendre accessible au plus Motivated by a desire to make the grand nombre le résultat des results of its graduate students' travaux de recherche menés par ses research accessible to all, and in étudiants gradués et dans l'esprit des accordance with the rules règles qui régissent le dépôt et la governing the acceptation and diffusion des mémoires et thèses diffusion of dissertations and produits dans cette Institution, theses in this Institution, the l'Université du Québec à Université du Québec à Chicoutimi (UQAC) est fière de Chicoutimi (UQAC) is proud to rendre accessible une version make a complete version of this complète et gratuite de cette œuvre. work available at no cost to the reader. L'auteur conserve néanmoins la The author retains ownership of the propriété du droit d'auteur qui copyright of this dissertation or protège ce mémoire ou cette thèse. thesis. Neither the dissertation or Ni le mémoire ou la thèse ni des thesis, nor substantial extracts from extraits substantiels de ceux-ci ne it, may be printed or otherwise peuvent être imprimés ou autrement reproduced without the author's reproduits sans son autorisation. permission. II UNIVERSITE DU QUÉBEC Á CHICOUTIMI THESE PRÉSENTÉE Á L'UNIVERSITÉ DU QUÉBEC Á CHICOUTIMI COMME EXIGENCE PARTIELLE DU DOCTORAT EN INGÉNIERIE PAR OMID LASHKARI LE COMPORTEMENT RHEOLOGIQUE DE L'ALLIAGE A356 SEMI-SOLIDE JUILLET 2006 Ill (Dedicated to Mama for her emotionalandspiritualsupports IV ABSTRACT The semi-solid-metal, SSM, processing deals with semi solid slurries, in which non dendritic solid particles are dispersed in a liquid matrix with apparent viscosity values near to that of liquid. It is able to flow easily under pressure and fills complicated die cavities to manufacture sound as-cast products with high integrity. The SSM slurry is prepared through different methods. In the current study conventional casting and the SEED process were employed to produce SSM billets with different morphologies of primary a-Al phase in A356 Al-Si alloy. For conventional casting, a range of solid particle morphologies, microstructure, were realized through variation of pouring temperature while for the SEED billets, as a new patent of ALCAN international for semi solid casting, changes in the morphology were achieved by control of process parameters during solidification of the melt. In order to investigate the morphological evolution due to the effect of different process parameters, pouring temperature and swirling intensities, the SSM billets prepared by both methods were studied using quantitative metallography. The microstructure of SSM A356 alloy has also been characterized using an innovative method, parallel plate compression viscometry, where a correlation was made between the morphology and viscosity. The main objective of the current research was the implication of rheological principles to study the deformation behavior of A3 5 6 alloy at different morphologies and fraction of solid, while treating the SSM billets as Newtonian and Non-Newtonian fluids respectively. Furthermore, two empirical relationships were proposed to underline the correlation among the viscosity, and fraction solid and its morphology. In order to further confirm the reliability of the tests results in this research and to highlight that the sample size has no effect on the final deformation and viscosity values, a new series of tests were performed using two sets of specimens with aspect ratio (height/diameter) of 0.4 and 1.8. It was found that conventional billets cast at low pouring temperature of 615°C comprise fine and equiaxed grains while the billets cast at high pouring temperature of 695°C have dendritic structure. For SEED billets, swirling refined the primary a-Al dendrites and promoted the formation of rosette and/or globular a-Al particles with increasing swirling speed. The effectiveness of swirling speed may be due to reduction in segregation of alloying elements at the solidification front and better heat transfer between the mold and bulk of liquid to establish a shallow temperature gradient resulting in refining and formation of equiaxed as- cast structure. There was no evidence of entrapped eutectic within the primary a-Al particles as one of the advantages of SEED slurry-on-demand technology. The reduction of pouring temperature down to liquidus point, 615°C, improved the flow characteristics of the billets. The calculated viscosity for the billets with globular primary a-Al particles are almost three orders of magnitude smaller than that for the fully dendritic structure. The difference reduces to one order of the magnitude in the case of rosette morphology compared to that of globular. Application of swirling during solidification has an obvious effect on the deformability and viscosity of the SEED prepared SSM billets. For the billets cast at 695°C, the results show superior deformation and lower viscosity at high swirling intensity due to the globular structure of the billet. Decreasing the swirling intensity brings some degree of resistance against deformation due to presence of rosette or dendritic morphology. For the V billets cast at 645°C, once the swirling is applied the engineering strain increases. In the case of 630°C, swirling is important to induce uniform temperature distribution across the bulk liquid where the resulting globular structure renders better deformability. The magnitude of applied pressure is also an important parameter in differentiating between the structures. The refinement of the grains has been identified as the main factor for better deformability of the billets. Modification also plays an important role on alloy deformability through reduction of the residual liquid surface tension which reduces the apparent viscosity of the billets. Two empirical equations were presented for rheological behavior of the SSM billets using viscosity as the principal parameter; Iog7 = 5.56-1.39/, -(1.56/,+0.14)logy Iog7 = -1-85 + 4.9AR - (0.255 AR + 0.03) log y The empirical relationships express the direct effect of fraction solid and morphology on the viscosity of semi solid billets. The validity of these equations was further confirmed with plotting log viscosity against shear rate for different fractions solid and morphology and a good agreement was found between the predicted values and the previously reported results in the literature. The irrelevance of sample size effect on the viscosity of SSM billets was also confirmed, where the same engineering strain and viscosity values were obtained for both large scale billets and small size disks. The current thesis reported that using large scale samples, the axial movement of the billets could be neglected against the radial flow during the steady state deformation stage, where the magnitude of viscosity values, are within the same range for both the sets of samples; (— > 1 ) and (h«d ) respectively. VI RESUME Le traitement du métal semi-solide, MSS, fait référence a des gelées semi-solides contenant des particules non dendritiques qui sont dispersées dans une matrice liquide, le tout ayant une viscosité apparente voisine de celle du liquide. Cette masse peut s'écouler facilement sous pression et remplir les cavités complexes d'un moule pour fabriquer des produits de qualité et de haute-intégrité. La gelée de MSS peut être préparée par différentes méthodes. Dans la présente étude la coulée conventionnelle et la procédure SEED ont été utilisées pour produire des billettes de MSS avec différentes morphologies de la phase primaire a-Al dans l'alliage Al-Si A356. Pour la coulée conventionnelle, une gamme de morphologies de particules solides et de microstructures, ont été obtenues en variant température d'alimentation. Pour les billettes SEED, nouveau brevet d'ALCAN international pour la coulée semi-solide, les changements de morphologies ont été réalisés en contrôlant les paramètres du procédé pendant la solidification de la masse. Afin d'étudier l'évolution morphologique due à l'effet des différents paramètres du procédé, la température d'alimentation et les intensités de brassage, les billettes MSS préparées par les deux méthodes ont été étudiées en utilisant la métallographie quantitative. La microstructure de l'alliage de MSS A356 a été également caractérisée en utilisant une méthode innovatrice, soit la viscométrie par la compression entre plaques parallèles, ce qui a permis d'obtenir une corrélation entre la morphologie et la viscosité. L'objectif principal de la présente recherche était de tirer partie de principes rhéologiques pour étudier le comportement à la déformation de l'alliage A3 56 pour différentes morphologies et fractions solides, en traitent des billettes de MSS comme des fluides newtoniens et non newtoniens, respectivement. En outre, deux relations empiriques ont été proposées pour mettre en évidence le lien entre la viscosité, la fraction solide et la morphologie. Afin de confirmer d'avantage la fiabilité des résultats des tests et de montrer que la dimension de l'échantillon n'a aucun effet sur les valeurs finales de la déformation et de la viscosité, une nouvelle série d'essais a été réalisée en utilisant deux types de spécimens ayant un rapport d'aspect (hauteur/diamètre) de 0.4 et de 1.8. On a constaté