Trans. Nonferrous Met. Soc. China 24(2014) 2482−2488 Effects of compocasting process parameters on microstructural characteristics and tensile properties of A356−SiC p composites Hamed KHOSRAVI, Hamed BAKHSHI, Erfan SALAHINEJAD Faculty of Materials Science and Engineering, K.N. Toosi University of Technology, Tehran, Iran Received 22 October 2013; accepted 21 March 2014 Abstract: The effects of compocasting process parameters on some structural and tensile characteristics of the A356−10% SiC p (volume fraction) composites were studied. Semisolid stirring was carried out at temperatures of 590, 600 and 610 °C with stirring speeds of 200, 400 and 600 r/min for 10, 20 and 30 min. The distribution of the SiC particles within the matrix, porosity content and tensile properties of the obtained samples were examined. The structural evaluations show that by increasing the stirring time and decreasing the stirring temperature, the uniformity in the particle distribution is improved; however, by increasing the stirring speed the homogeneity firstly increases and then declines. It is also found that by increasing all of the processing parameters, the porosity content is enhanced. From the tensile characteristics viewpoint, the optimum values of the speed, temperature and time are found to be 400 r/min, 590 °C and 30 min, respectively. The contribution of the reinforcement distribution uniformity prevails over that of the porosity level to the tensile properties. Key words: A356−SiC p composite; semisolid stirring; compocasting; porosity; reinforcement distribution; tensile properties 1 Introduction Metal-matrix composites (MMCs) are widely used in various industries, such as aerospace, aircraft, automotive, agriculture, mining and manufacturing. The impetus behind the development of MMCs is the ability to obtain a desired combination of properties which are not obtainable in monolithic materials. The addition of high strength and high-modulus particles to a ductile metal matrix produces a material whose mechanical properties are intermediate between the matrix alloy and the ceramic reinforcement. Recently, MMCs have received substantial attention because of their improved strength, high elastic modulus, low thermal expansion coefficient and increased wear resistance over conventional based alloys. For these materials, silicon carbide (SiC) particles have become the main type of reinforcement used due to their good compatibility with aluminum alloys together with their low cost as well as excellent thermal, physical and mechanical properties. However, the increase in strength and stiffness occurs at the expense of toughness [1−7]. MMCs are produced via different routes, mainly casting and powder metallurgy techniques. The fabrication of particulate reinforced MMCs by casting methods is commercially practiced over the past decades, due to its potential in terms of production capacity and cost efficiency. Among casting techniques, stir casting is the most frequently used route to produce particulate MMCs. However, it is associated with some inherent problems arising mainly from both the apparent non-wettability of ceramic reinforcing particles by liquid aluminum alloys and the density differences between the two phases [8,9]. In order to overcome some of these drawbacks that result in the non-uniform distribution of the reinforcement within the matrix alloy, extensive interfacial reactions and formation of brittle phases at the particle/matrix interface as well as a high level of porosity, new semi-solid processing techniques have been considered for manufacturing these MMCs [10−12]. Compocasting is a semi-solid processing route in which ceramic reinforcing particulates are added to a semi-solid matrix alloy via mechanical stirring. This technique has two different variations, namely semisolid−semisolid (SS) and semisolid−liquid (SL). In both of the variations, the matrix alloy during the mixing step is in the semi-solid state, while the matrix during the casting step is partially liquid or fully liquid for the SS Corresponding author: Hamed KHOSRAVI; Tel: +98-9151177285; E-mail: hkhosravi@mail.kntu.ac.ir DOI: 10.1016/S1003-6326(14)63374-4