Examination of the stir-casting method to produce Al-SiC composites

摘要

This work examined the influence of processing parameters on the production of Al-SiC metal matrix composites (MMC) by batch compocasting process. Processing parameters investigated includes tirring speed, stirring time, stirrer geometry, stirrer position , metal fluid temperature (viscosity). Room temperature (25°C) visual simulations, computer simulations and validation Al-SiC MMC production tests were performed.ududIn the visual and computer simulations, water an d g ly c e ro l/water were used to represent liquid an d semi-solid a lum in ium respectively. The effects of viscosities of 1, 300, 500, 800 and 1000 mPas and stirrin g speeds of 50, 100, 150, 200, 250 and 300 rpm were investigated. A 10 vol. % reinforced SiC particulate , similar to that used in the aluminium MMC’s, was used in the visualisation and computational tests. The visualisation tests were carried out in a transparent glass beaker. The computational simulation was performed with Fluent(CFD software) an d an ad d on package MixSim. This consisted of a 2D axisym metric multip h a se time dependent simulation of the production routeusing an Eulerian (granular) model. The dependence of particle dispersion times, settling timesand vortex height on stirring geometry and stirrer speed was found. A blade angle of 60 degrees was found better for the flat blade stirrer, to obtain uniform particulate dispersions quickly. From the setestsas tirrin g speed of 150 rpm for water-SiC an d 300 rpm for the glycerol/water-S iC sy stem were found to be necessary in order to obtain a uniformd is tribution of the SiC. A viscosity increase from 1 mPas (for liquid metal) to 300 m Pas (for semi-solid metal) was found to have a tremendous effect on the SiC dispersion and settling times. However, a further increase from 300 mPas to 1000 mPashad negligible effect on this time. A significant part of the work consisted of the design, construction and validation of a specialised quick quench compocaster for this high temperature processing method. This machine consisted of a stirrer with four 60 degree angled flat blades and a cruciblein a resistance heated furnace chamber. An actuator was integrated to this rig to enable quick quenching of the processed mixture. This device was used to produce Al-SiC composites. Generally, good agreement was found between the visualisation, computational and validation experimental results.