MORPHOLOGICAL CHARACTERIZATION OF Al-2.0wt%Si-2.5wt%Cu ALLOY PRODUCED BY DIRECT CHILL CASTING AND ELECTROMAGNETIC STIRRING FOR THIXOFORMING PROCESS L.V. Torres 1,a , D.M. Benati 1,b , E.J. Zoqui 1,c 1 Manufacturing Department, Faculty of Mechanical Engineering, University of Campinas – UNICAMP, P.O. Box 6122, CEP 13083-860, Campinas, SP, Brazil a torres@fem.unicamp.br; b dmbenati@fem.unicamp.br; c zoqui@fem.unicamp.br Key-words: semi-solid materials, thixoforming, electromagnetic stirring. Abstract:This work evaluates, by means of its morphological characterization, a new Al-2.0wt%Si- 2.5wt%Cu alloy produced by direct casting under electromagnetic stirring for thixoforming process. The alloy was submitted to re-heating treatment in two conditions of solid fractions, 45% and 60%, for 0, 30, 90 and 210 s. Re-heating treatment times promote solid phase particles globularization, presenting average grain sizes of approximately 90 µm for both solid fraction. These results show that the alloy is viable for thixoforming process, especially in the condition of 90 s of treatment time at 45% and 60% of solid fraction, that presents grain size about 90 µm and shape factor higher than 0.60. Another important fact about the small grain/primary particle size is related to the use of electromagnetic stirring in its production, that promotes the breakdown of the material structure and consequently stimulates globularization. INTRODUCTION Al-Si rheocast alloys have been used widely for thixoforming processes. A356 and A357 are the most common alloys used to obtain near net shape products [1,2]. However, all these alloys are casting alloys, fitted to the thixoforming purpose. Thus, there is a lack of specific alloys for semi- solid processing that present good fluidity, low viscosity and small grain size, i.e. vital metallurgical characteristics that lead to the best semi-solid behavior [3,4]. In the last decade, the automotive industry has played a leading role in the development of new processes for manufacturing parts using semi-solid materials. The use of aluminum in automobiles, primarily in the form of castings, has increased significantly due to the need to produce parts with high mechanical strength, low weight and high reliability [5,6] and for casting near net shape products offers benefits such as energy savings, fewer production steps, greater productivity and higher overall quality [7]. The aim of this work is to contribute to the body of knowledge about thixoforming through an in-depth analysis of the Al-2.0wt%Si-2.5wt%Cu alloy produced by direct chill casting under intense electromagnetic stirring. EXPERIMENTAL PROCEDURE The thixotropic raw material used in this experiment was the Al-2.0wt%Si-2.5wt%Cu alloy produced by electromagnetic stirring combined with grain refinement. After the material reached the desired casting temperature, it was poured into a sealed mold coupled to an electromagnetic stirring system, consisting of a series of coils wrapped around the chilled mold; approximately 8 kW of power was used to produce a magnetic field. Prior to casting, a grain refiner was added to the material to enhance the effect of electromagnetic stirring. Table 1 describes the chemical composition of the alloy characterized by optical emission spectroscopy. Materials Science Forum Vols. 775-776 (2014) pp 118-123 Online available since 2014/Jan/03 at www.scientific.net © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/MSF.775-776.118 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: 143.106.21.40, University of Campinas, Campinas, Brazil-05/02/14,14:03:08)