Modeling of the reactive immersion of ceramic particles into molten aluminium alloys

In this work, the chemically assisted immersion of SIG, Si3N4 and Mg3N2 particles into a molten aluminum alloy was experimentally investigated for different processing times and temperatures. Prior to the introduction of SiC particles into the melt, their surface chemical composition was changed in various ways in order to promote exergonic interfacial reactions between the applied surfactants and the melt. In this way, the activation energy of the overall process of immersion was calculated for each interfacial reaction applied. Si3N4 and Mg3N2 were introduced into the melt in the as-received condition. The investigation showed that the volume fraction of particles successfully immersed increases linearly with time of immersion and exponentially with the temperature of the molten aluminum alloy. It was also evident that the volume fraction of ceramic reinforcement increases with the lowering of the activation energy of the interfacial chemical reaction. In this way, use of an interfacial reaction with a low activation energy routinely resulted in a composite with more than 20 vol.% of ceramic particles dispersed into the melt. The calculated activation energy for chemically assisted immersion corresponds to the activation energy of the interfacial reaction applied. On this basis, it is likely that the rate-limiting step in the overall process of chemically assisted immersion is probably determined by the kinetics of the applied interfacial reaction. A theoretical explanation of these findings is offered on the basis of the general assumption that there is a contribution from the free energy released by the applied interfacial reaction to wetting behaviour between the ceramic particles and the melt. (C) 1999 Elsevier Science Ltd. All rights reserved.