Microstructural evolution and Wear properties of In-situ Al-4.5Cu-5TiB 2 Composite Processed in Mushy State Mervin A. Herbert 1,a , R. Maiti 2,b , R. Mitra 1,c and M. Chakraborty 1,d 1 Department of Metallurgical & Materials Engineering 2 Central Research Facility, Indian Institute of Technology, Kharagpur-721302, West Bengal, India , mer@nitk.ac.in, b rabin_maiti@hotmail.com, c rahul@metal.iitkgp.ernet.in, d madhu@metal.iitkgp.ernet.in Keywords: In-situ Composite, Mushy-state Rolling, Alligatoring, Microstructure, Hardness, Wear. Abstract. In-situ Al-4.5Cu-5TiB 2 composite plates were stir cast with TiB 2 particles formed through mixed salt route. The as-cast samples with 30 volume percent liquid content were rolled in mushy state down to 2.5 and 5 percent reduction in thickness per pass. The rolled products found to be defect-free after the first pass were subjected to multiple roll passes in mushy state with identical experimental conditions, adding up to seven. The wear properties of as-cast and mushy state rolled composites were also investigated, and correlated with microstructure. Introduction In recent years, considerable attention has been given to mushy state processing of commercial alloys and metal-matrix composites as the power required for deformation is reduced because of the lower flow stress compared to that in solid state [1]. The mechanism of plastic deformation is altered by the presence of liquid such that strain accommodation occurs through flow of liquid metal at grain boundaries and intragranular slip inside the unmelted grains, with the contribution of the former increasing with liquid content [2]. The process is particularly relevant for working of materials, which are difficult to form through conventional methods. It is difficult to near-net shape Al-matrix composites by machining or forming, and thus mushy state rolling provides a viable alternative forming method. Thixo-forging and thixo-extrusion of composites have been studied earlier [3, 4]. However, little information exists on rolling of composites in mushy state. The present study on Al-4.5 wt.% Cu-5 wt.% TiB 2 particulate composites is an attempt to understand the evolution of microstructure after each roll pass and its effect on hardness and wear properties. Experimental Procedure Processing: An Al-33 wt% Cu master alloy with suitable amount of aluminium was melted in an induction furnace in order to obtain Al-4.5 wt. % Cu alloy. Subsequently TiB 2 particle were formed in-situ by mixed salt process [5] involving reaction of K 2 TiF 6 and KBF 4 with molten Al: K 2 TiF 6 + KBF 4 + Al TiB 2 + K 2 AlF 4 (1) A graphite crucible housed inside a pit furnace was used to melt-process the composite, which was subsequently stir-cast into plate-shaped cast iron moulds. Mushy state rolling: Fig. 1 presents a schematic illustration of mushy state rolling. A two-high mill with rolls of 120 mm diameter and 125 mm barrel width was used for the experiments. In order to promote instantaneous solidification during mushy state rolling, the surface temperature of the roll was kept at ambient temperature. The specimens with dimensions of Solid State Phenomena Vols. 116-117 (2006) pp. 217-220 online at http://www.scientific.net © (2006) Trans Tech Publications, Switzerland 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 the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net . (ID: 202.63.233.11-10/10/06,08:08:58)