Microstructure and corrosion behaviour of aluminium fly ash composites

The microstructural characteristics of aluminium matrix MM composites containing of fly ash particles (precipitator), obtained by gravity and squeeze costing techniques, pitting corrosion behaviour and corrosion kinetics are presented and discussed. It was found that: (1) in comparison with gravity casting, squeeze casting technology is advantageous for obtaining higher structural homogeneity with minimum possible porosity levels, good interfacial bonding and quite a uniform distribution of reinforcement, (2) fly ash particles lead to an enhanced pitting corrosion of the AK12/9.0% fly ash (75-100 mum fraction) composite in comparison. with unreinforced matrix (AK12 alloy), and (3) the presence of nobler second phase of fly ash particles, cast defects like pores, and higher silicon content formed as a result of reaction between aluminium and silica in AK12 alloy and aluminium fly ash composite determine the pitting corrosion behaviour and the properties of oxide film forming on the corroding surface.