Study on Thixotropic Property of A356 Alloy in Semi-Solid State Sudip Simlandi 1, a , Nilkanta Barman* 1,b and Himadri Chattopadhyay 1,c 1 Department of Mechanical Engineering, Jadavpur University, Kolkata- 700032, India a sudip.simlandi@gmail.com, b nilkantajdvu@yahoo.com, c chimadri@gmail.com Keywords: Thixotropic behavior, Modelling, Apparent viscosity Abstract. In the present work, the thixotropic property of a semisolid aluminium alloy (A356) under deformation is investigated numerically where the flow between two parallel plates is considered. The flow field is represented by momentum conservation equations where the non- Newtonian behavior of the semisolid material is represented by the Herschel-Bulkley model. The agglomeration and the de-agglomeration phenomena of the suspended particles under shear are represented using a time dependent structural parameter influenced by the rate of strain and shear stress. The simulation predicts the flow field, rate of strain and apparent viscosity of the semisolid materials under transient and steady state conditions. It is found that the apparent viscosity shows a transient nature during sudden change in the shear rate, and its value decreases with increasing shear rate and vice-versa. It is also found that the present prediction shows a good agreement with prior work. Introduction The thixoforming is a developing manufacturing technique which produces near-net-shape components. This technique is much advantageous over the other conventional forming techniques such as it consumes less energy, and the final products have low porosity and good mechanical properties. In thixoforming, the alloys are deformed in semisolid state, which exhibits a complex non-Newtonian flow behavior. The flow behavior is influenced by numerous process factors, and depends on time and stress history. In literature, it is found that the theoretical models for such semisolid materials under deformation are less developed and the available constitutive models are mostly established from experiments. However, for successful implementation of the technique, proper knowledge on the properties of the semisolid materials under deformation is necessary. In the present work, therefore, the thixotropic property of a semisolid alloy under deformation is investigated numerically. For understanding the modelling of the thixotropic behavior of alloys in semisolid state, related research works are reviewed. Burgos et al. [1] reported that there exists a shear-dependent finite yield stress which is modeled using the Herschel-Bulkley fluid model and introducing a structural parameter to describe the kinetics of the agglomeration and de-agglomeration phenomena. Koke and Modigell [2] found that the yield stress is strongly depends on the microstructure and the degree of agglomeration of the solid phase and increases strongly with rest time because of the agglomeration of the suspended solid particles. They also found that the steady-state rheological behavior is shear thinning. Gautham and Kapur [3] presented a model for unsteady state shear stress of the semi-solid metal suspensions by introducing a structural parameter. Dullaert and Mewis [4] presented a general structural kinetics model to describe the flow behavior of thixotropic systems. A model proposed by Alexandrou [5] is able to predict the flow behavior of the semi-solid slurries. In that work, the variation of an apparent viscosity demonstrates the complexity of the flow behavior of slurry. Alexandrou et al. [5, 6] presented the rate of breakdown and rate of buildup in semi-solid slurry during shearing. They used the Herschel-Bulkey model as a standard thixotropic model for modeling of the semi-solid metal suspensions. However, the semisolid alloys show a complex and distinct flow behavior during semisolid processing. This complex flow behavior during processing changes the process variables and conditions continuously in a way that is very different than the convectional processing. Therefore, it is essential to generate concept and ideas of the alloy Solid State Phenomena Vols. 192-193 (2013) pp 335-340 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/SSP.192-193.335 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 203.197.118.111-21/09/12,13:39:32)