* Graduate Student at McGill University. JOURNAL OF MATERIALS SCIENCE 33 (1998) 4381 — 4387 Thermal expansion of isotropic Duralcan metal–matrix composites S. LEMIEUX * , S. ELOMARI Spacecraft Engineering, Canadian Space Agency, 6767 route de l’Aeroport, Saint-Hubert, J3Y 8Y9, Canada E-mail: elomari@colba.net J. A. NEMES Department of Mechanical Engineering, McGill University, Montreal, Canada M. D. SKIBO MC-21 Incorporated, San Diego, CA 92121, USA The thermal expansion behaviour of Duralcan composites having a matrix of hypoeutectic Al—Si alloy containing SiC reinforcements ranging from 10—40 vol% was investigated. The coefficient of thermal expansion (CTE) of the MMCs was measured between 25 and 350 °C by a high-precision thermomechanical analyser, and compared to the predictions of three theoretical models. At low temperature, the experimental CTEs show substantial deviation from the predictions of the elastic analysis derived by Schapery, while the Kerner model agrees relatively well at high temperature. The overall measured CTE, in the range of 25—350 °C, as a function of the volume fraction of SiC is well predicted using Schapery’s lower bound. We interpret these features as being an effect of reinforcement phase geometry and the modified microstructure derived from the Duralcan process and subsequent heat treatments.  1998 Kluwer Academic Publishers 1. Introduction Metal matrix composites (MMCs) have emerged as a class of materials capable of advanced structural, aerospace, automotive, electronic, thermal manage- ment, and wear applications. These alternatives to conventional materials provide the specific mechan- ical properties necessary for cryogenic and elevated temperature applications. In many cases, the perfor- mance of MMCs is superior in terms of improved physical, mechanical, and thermal properties. The per- formance advantage of aluminium alloys reinforced with various ceramics such as SiC and Al  O  is their tailored mechanical, physical, and thermal properties that include low density, high specific strength, high specific modulus, good fatigue response, control of thermal expansion, high abrasion and wear resistance [1, 2]. Tailorability for specific applications is one of the greatest attractions of MMCs. Thus, these com- posites are gaining rapid prominence in aerospace [3], automotive, electronic [4] and energy sectors. For instance, low coefficient of thermal expansion (CTE) and high thermal conductivity are desirable properties for applications such as heat sink and radiator panels for satellite structures and space shuttles [5]. Further- more, MMC material is being successfully used as diecast components, which include pistons [6, 7], cy- linder liners, connecting rods [8], brake drums and even engine blocks. The interest in this composite stems from its high specific strength and stiffness, low thermal expansion, high thermal conductivity and im- proved tribiological properties. The CTE of MMCs has been recognized as one of the important thermomechanical properties because the thermal stability can be a critical issue in the design of components subjected to temperature vari- ations. Tailoring the CTE is an important considera- tion in minimizing the expansion—contraction mismatch or to maintain specific dimensional toleran- ces between components subjected to various temper- ature gradients. In addition, a thermal expansion study of MMCs is required in order for thermal stres- ses to be investigated for particular applications such as electronic packaging. In recent years, extensive numerical and analytical research has been performed on thermomechanical properties, such as CTE, of Al/SiC composites and on the dependence of such properties on processing para- meters [9, 10]. For instance, it has been well estab- lished from numerical investigations that geometrical variables, such as the concentration, size, shape, and spatial distribution (architecture) of the ceramic particles in the aluminium matrix can substantially influence the thermal expansion behaviour of particle- reinforced MMCs. However, detailed experimental 0022—2461  1998 Kluwer Academic Publishers 4381