Thixoforming of Aluminium-silicon Alloys in a Mechanical Eccentric Press Eugênio J. Zoqui 1,a , Luciano A. Lourençato 2,b and Davi M. Benati 3,c 1,2,3 Dept. of Manufacturing, Faculty of Mechanical Engineering, UNICAMP C. Postal 6122, Campinas 13083-860, SP, Brazil a zoqui@fem.unicamp.br, b lalouren@fem.unicamp.br, c dmbenati@fem.unicamp.br Keywords: thixoforming; semisolid material; eccentric press; aluminium-silicon alloys Abstract. The semisolid processing technology is not widely used due to the high cost of raw material and the equipment it requires. New low-cost raw materials and processes could be the key to expand the use of this technology. This paper describes an initial effort to develop new Al-Si-Mg in terms of raw material production and processing. The morphological evolution of all the alloys produced was characterized during their reheating to the semisolid state at 45 and 60% solid fraction, as well as the semisolid behaviour in terms of viscosity versus shear rate. The adaptation of the semisolid technology to the thixoforming process via eccentric press was tested using an equipment up to 25 tons. This type of equipment is not commonly employed in this kind of processing. Results indicate that alloys with low silicon content, e.g., 2 or 4wt%Si, behave similarly to alloys with 7wt%Si, which are normally used in the thixoforming process, with a viscosity of about 2 * 10 5 Pa.s. The semisolid behaviour of low silicon alloys indicates the potential expansion of the range of raw materials for this application. Thixoforming of semisolid materials in an eccentric press appears to be a very promising technology, yielding parts that, despite their simplicity and restricted shape, display a very good final mechanical behaviour. Introduction Semisolid raw material (SSM), which is more expensive than the raw material normally used in the conventional process, typically costs 150% more than die casting material and 125% more than squeeze casting or permanent moulding material. A comparison of the overall costs of tooling, capital, labour, heat treatment, machining, finishing, etc. indicates that bottom-line casting costs are about 100% higher than those of die casting, but 10% lower than squeeze casting and 50% lower than permanent moulding. Hence, the SSM process offers economic advantages, although this technology is still expensive [1]. The development of new low-cost alloys and a new low-cost process could be the key factor for the dissemination of this technology. Previous papers described attempts to produce such raw materials using ultra-grain refining (UR) [2,3,4] and electromagnetic stirring (EMS) techniques [5,6]. They showed that the viscosity of the Al-Si alloys system varies very little as a function of the solid fraction, and that a low-silicon alloy can have almost the same viscosity as the A356 alloy [2,6,7]. This paper discusses the rheological behaviour of several alloys as a function of heat treatment at 45% and 60% solid fraction of aluminium-low silicon alloys produced by UR, and describes the thixoforming of those alloys in an eccentric press using an open die. Experimental Procedure Raw Material Production. Four alloys were produced by the ultra-grain refining method using Al-5wt%Ti-1wt%B in small crucibles: Al-1wt%Si-0.5wt%Mg, Al-2wt%Si-0.5wt%Mg, Al-4wt%Si-0.5wt%Mg, and Al-7wt%Si-0.5wt%Mg (A356 as comparison), with up to 0.2wt%Ti, which grain size have the Ti particles. The molten alloys were poured into a 30mm diameter, 250mm high metallic mould, resulting in twelve 470g billets of each alloy. An acceptable deviation range of Solid State Phenomena Vols. 141-143 (2008) pp 517-522 Online available since 2008/Jul/07 at www.scientific.net © (2008) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/SSP.141-143.517 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-12/08/14,14:43:31)