Fabrication and microstructure characterization of fly ash containing aluminyum matrix composites

ABSTRACT In recent years there has been a great deal of interest in particulate-reinforced metal-matrix composites (MMCs), and in particular those based on existing aluminium alloys. This is because the addition of ceramic particles to duminium alloys, as a function of volume fraction (Vf) can lead to improvements in elastic modulus, yield stress, tensile strength, wear resistance and hardness, although invariably accompanied by reductions in ductility and fracture toughness. Also controlled, low thermal expansivity and thermal conductivity meet engineering requirements. Despite these attractive properties, fabrication of composites having high mechanical and physical properties, requires advanced technology, regarding to the fabrication process and reinforcing chosen. To eliminate these restrictions on composite fabrication, application of low cost reinforcements and uncomplicated production process should be encouraged. Cost saving in composite fabrication process, reinforcement, and utilisation of coal combustion by-products (fly ash) aimed in this research work. AMC's fabricated from ETÎAL 171 (A360) and ETÎAL 120 (443) aluminium alloys and Tunçbilek, Yatağan fly ashes were used as reinforcement with volume fractions %5, %10, %15, %20. Stir mixing and casting process were used for the fabrication of fly ash containing aluminium-matrix composites (AMC's). Specially designed and ceramic covered mixer were used for string of melted aluminium alloy at 750, 850, 950 °C elevated temperatures and 400, 560, 750 rpm rotation rates. Variation of limited parameters such as, string and casting temperatures, string rate, mixer geometry, oxidation tendency, difficulties in homogeneity of particle distribution can be classified as a limitation of a fly ash containing AMC fabrication. Proposals for the elimination of these restrictions were presented in relevant sections. It has been observed that, with the applied fabrication process, maximum %20 (volume) fly ash can be added to aluminium alloy matrix. Addition of fly ash, over volume fractions (Vfmax) %20 tend to effect wetting ability and fluidity of aluminium alloy melt were also observed. Tensile, hardness, wear, elastic modulus, density, bend, impact tests applied to investigate mechanical and physical properties of fabricated AMK specimens and optical, scanning electron microscope micro graph were taken for microstructure characterisation. Referring to the experimental data, optimum properties were achieved at 850 °C string temperature and 560 rpm mixer rotation rates. From the test results, up to % 15 reinforcement volume fractions, increase in wear resistance, hardness, tensile strength, elastic modulus and decrease in elongation and impact strength were observed as a function of reinforcement volume fraction (Vf). With this application, utilising low cost fly ash as a filler material, significant amount of aluminium alloy can be saved, in commercial fabrication of reinforced aluminium alloy tools. XI