AZ91 magnesium matrix foam composites with fly ash cenospheres fabricated by negative pressure infiltration technique

The feasibility of fabricating magnesium matrix foam composites with fly ash cenospheres by the negative pressure infiltration technique has been demonstrated. An AZ91 commercial magnesium alloy was chosen as the matrix. Two kinds of hollow aluminosilicate cenospheres, as-received and NiP coated, were used in this study in order to determine the influence of the NiP coating on the composite microstructure. Analyses of the fabricated composite microstructures were carried out by light microscopy, the X-ray diffraction technique, scanning electron microscopy and the Raman spectroscopy method. Additionally, the theoretical and measured density of the fabricated composites was analysed. Composites fabricated by the negative pressure infiltration technique were characterised by uniform distribution of 60 vol% cenospheres. Both cenospheres filled and unfilled by the matrix alloy were observed in the composite with as-received fly ashes. Mg2Si and MgO compounds were revealed as products of reactions between the components in this material. In contrast, intact hollow cenospheres were present in the microstructure of the composite with NiP coated cenospheres. This composite had a minimum value of measured density equal to 1.1893 g/cm3, which was in agreement with the theoretical value calculated using the rule of mixtures.