JOURNAL OF MATERIALS SCIENCE 36 (2 0 0 1 ) 419 – 428 Interfacial reactions in an Al-Cu-Mg (2009)/SiCw composite during liquid processing Part I Casting A. UREI ˜ NA ∗ , P. RODRIGO, L. GIL Dept. Ciencias Experimentales e Ingenier´ ıa. Escuela Superior de Ciencias Experimentales y Tecnolog´ıa, Universidad Rey Juan Carlos, 28933 M´ ostoles, Madrid, Spain E-mail: a.urena@escet.urjc.es M. D. ESCALERA Dept. Ciencia de los Materiales e Ingenier´ ıa Metal ´ urgica, Facultad de Ciencias Qu´ ımicas. Universidad Complutense de Madrid, 28040 Madrid, Spain J. L. BALDONEDO Centro de Microscop´ ıa Electr ´ onica “Luis Bru”, Universidad Complutense de Madrid, 28040 Madrid, Spain The interfacial reactions in an aluminium alloy composite (AA2009) reinforced with 15% volume of SiC whiskers were studied. The composite was subjected to a simulated casting process to analyse its response under different melting conditions. The different reaction mechanisms between the SiC whiskers and both the molten aluminium and their alloying elements (Cu, Mg, and Fe) are discussed. The high aspect ratio (l /d ) of the reinforcement is the main microstructural factor, which controls both reactivity and wettability between the molten matrix and the SiC. Tested specimens showed very great Si-enrichment of the matrix around SiCw which produced an isothermal solidification and stopped the interfacial reactions. Formation of binary aluminium carbide (Al 4 C 3 ) during the melting cycles was also detected, especially for temperatures higher than 800 ◦ C, produced by a dissolution-precipitation mechanism. Nucleation of the Al 4 C 3 crystal was favoured both on the lateral whisker surfaces and on oxide particles (Al 2 O 3 , MgO) present in the aluminium matrix. Transmission Electron Microscopy and Electron Diffraction (TEM-ED) studies made it possible to identify both the nature and the structure of the different interfacial products generated during casting. C  2001 Kluwer Academic Publishers 1. Introduction Aluminium matrix composites (AMC) reinforced with ceramics have some greatly improved mechanical prop- erties, such as wear resistance, hardness, specific stiff- ness and strength, etc. as compared to unreinforced al- loys [1]. Of particular interest among these AMCs are those reinforced with ceramic whiskers in that this is a special kind of defect-free monocrystalline reinforce- ment with the highest strengths. They have a smaller diameter than continuous ceramic fibres, being a dis- continuous phase (with a finite l /d ratio). SiC whiskers (SiCw) are among those most widely used to rein- force aluminium alloys because of their advantages over other possible candidates (B, graphite, Al 2 O 3 , K 2 Ti 6 O 13 or Al 18 B 4 O 33 ). Their main characteristics include higher thermal conductivity, excellent corro- sion resistance, great machinability and formability, and above all low fabrication costs (from rice hull py- ∗ Author to whom all correspondence should be addressed. rolysis or vapour-liquid solid synthesis from coconut hull) [2, 3]. One of the main problems presented by Al-SiC com- posites, and particularity whisker reinforced compos- ites, is the difficulty of applying liquid phase procedures for their manufacture or joining. Most SiCw-AMCs are made by powder metallurgy (PM). Only the pressure in- filtration of whisker preforms as a cast fabrication route has been applied with acceptable results [4–6]. The in- terfacial reactions occurring during contact between the molten matrix and the reinforcement is one of the prob- lems that limits the processability of these composites. These problems not only affect the interface strength but also other aspects relating to the mechanical be- haviour of the matrix, such as age-hardening mecha- nisms, or wettability between the two components. The reaction between molten aluminium and SiC in the temperature range 650–900 ◦ C has been studied 0022–2461 C  2001 Kluwer Academic Publishers 419