Effect of fly ash addition on the magnesium content of casting aluminum alloy A535

Abstract

In the past few decades development efforts in the area of particle-reinforced metal matrix composites (MMCs) have focused mainly on age-hardenable aluminum alloy MMCs [1–14]. Particle-reinforced aluminum matrix MMCs are attractive for automobile, electronic packaging, and aerospace applications due to their low density, high specific strength and modulus, superior wear resistance and low coefficient of thermal expansion (CTE) [15, 16]. Most conventional particulate aluminum matrix MMCs are expensive and, as such, efforts are being made to produce aluminum alloy MMCs at lower costs and with similar, or possibly better, engineering application bases. Recent research into developing inexpensive aluminum alloy MMCs shows that fly ash can be used in forming inexpensive aluminum MMCs with improved mechanical properties that can compete favorably with other available particulate MMCs [16–28]. Fly ash is a lightweight coal combustion by-product (CCB) produced in upwards of 5 million tonnes annually in Canada by thermal generating utilities. It is separated from the exhaust gases of power plants with a suspension-fired furnace in which pulverized coal is used as fuel. It is generally finer than Portland cement and consists of small glassy spheres with varying sizes (ranging from less than 1 μm to more than 100 μm). Two major classes of fly ash are recognized, Classes C and F, which are related to the type of coal burnt [29, 30]. Class F fly ash, which is more suitable for the synthesis of MMCs because of its low CaO content, is generally obtained by burning anthracite or bituminous coal. The physical and chemical properties of fly ash make it useful for construction and industrial materials, especially in cement manufacturing, concrete, liquid waste stabilization, and hydraulic mine backfill. Using fly ash to reinforce aluminum alloy MMCs offers advantages of reducing disposal volumes for coal-powered utilities plants, providing a high value-added use of fly ash and producing composites with improved material properties (e.g., wear resistance