Aluminum/Fly Ash Syntactic Foams: Synthesis, Microstructure and Properties

Increasing demand to improve the fuel effi ciency and reduce pollution in the aerospace and automotive sectors, while retaining the integrity of structures, has resulted in the development of new advanced lightweight porous composites. Traditionally, porosity is considered to be an undesired microstructural feature in materials. However, an innovative method of using hollow particles to incorporate porosity in materials has shown great promise. Such composites, known as syntactic foams, have been widely studied in recent years. A number of engineered hollow particles are now available and are used as fi llers. Fly ash cenospheres, a waste by-product of coal-fi red power plants, are one such class of hollow particles that are commonly used in syntactic foams. Fly ash is generally inexpensive and is considered to be an environmental hazard, thus utilization of fl y ash in composites proves to be both economically and environmentally benefi cial. In this way, use of fl y ash in developing advanced composites is very encouraging for the next generation of advanced lightweight composites. The discussion in this chapter is focused on fl y ash fi lled aluminum matrix composites. Complex composition of fl y ash leads to several interfacial reactions and generation of reaction products, which can diffuse to short and long ranges depending on composite processing conditions (time and temperature). This discussion is focused on synthesis methods, microstructure, mechanical properties, and tribological properties of Al/fl y ash syntactic foams.