Infiltration of Al-Mg Alloy into SiC Preform in the Production of Metal Matrix Composites by Pressureless Infiltration

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Department of Metallurgy, The University of Indonesia, Kampus Baru UI, Depok 16424, Indonesia. Department of Engineering Materials, The University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK.

ABSTRACT Molten Al-Mg alloys has been infiltrated into SiC to produce Al matrix composites at 900oC for different infiltration times under N2. The wettability of the ceramic reinforcement by the Al-Mg alloy is crucial in determining whether Al can be infiltrated into ceramic preform. Sessile drop results showed that Al alloys with Mg contents greater than 8wt-% had a contact angle lower than 90o, after 5 minutes contact time, this was associated with the infiltration of Al-Mg alloys into SiC preform occurred after 30 minutes. Sessile drop experiments also show that SiC is similarly wetted by Al-Mg alloys under N2. It is concluded that the infiltration process does not involve the intermediate nitride phase suggested by other authors. These materials were also charaterised both mechanical properties and microstructure. 1. INTRODUCTION Metal matrix composites (MMCs) reinforced with ceramic reinforcements offer high strength and modulus, as well as good high-temperature properties, when compared to corresponding monolithic alloys and are promising materials for automotive and aerospace applications. MMC production via liquid metal infiltration has the potential to be an economic process, however the non wetting nature of many ceramics by molten aluminium, which result in poor ceramic metal interfaces and incomplete infiltration, are obstacles. Attempts to overcome these obstacles have usually involved the use of pressure or vacuum to assist the infiltration process [1,2]. However a more recent development in the production of aluminium matrix MMCs has been a pressureless infiltration process. The process involves the infiltration of a liquid Al-Mg alloy into a porous preform under N2 at atmospheric pressure, which means that the process can be carried out using simpler equipment than that required for vacuum or pressure assisted infiltration [3,4]. This infiltration process is related to the Lanxide or directed melt oxidation process for ceramic matrix composite production and has, in fact, been patented under the Primex™ name by the Lanxide Corporation. The relationship between infiltration pressure and wetting has been reported by Mortensen and Cornie [5]. For non-wetting systems they report that the pressure necessary for infiltration becomes infinitely large as the contact angle between touching reinforcements approaches 0. This necessitates the formation of voids at regions of filler (preform) contact. They argue that infiltration into these regions is actually preferred since the metal will be drawn into regions U8.6.1 1

Figure 4 : (a) SEM micrographs of Al10Mg alloy/SiC MMCs after pressureless infiltration at 900oC for 8 hours. (b) EDS o