The Role of Ni-P Coating Structure on Fly Ash Cenospheres in the Formation of Magnesium Matrix Composites

Abstract

The role of the Ni-P coating structure on fly ash cenospheres in the fabrication of magnesium matrix composites has been investigated. Two composites based on AZ91 commercial magnesium alloys with hollow aluminosilicate cenospheres were fabricated by the negative pressure infiltration technique. Two kinds of cenospheres (i.e., as Ni-P coated and after heat treatment) were used in order to determine the influence of the Ni-P coating structure on creating interfaces between the components. Microstructure analyses were carried out by light microscopy, atomic force microscopy, XRD, scanning, and transmission electron microscopy. Al3Ni2 and Mg2Ni intermetallic phases at the component interfaces were formed in the composite with as-received Ni-P-coated cenospheres. After heat treatment of the Ni-P-coated cenospheres, NiO was created outside the external layer of the Ni-P coatings and this oxide remained stable at the component interfaces during composite fabrication. In both cases, the Ni-P coating prevented the reaction between the cenosphere walls and the magnesium matrix alloy, which contributed to obtaining intact cenospheres, unfilled by the matrix alloy.