Microstructure and interface characterization of a cast Mg2B2O5 whisker reinforced AZ91D magnesium alloy composite

In this study, the microstructure and interface of a Mg2B2O5 whisker-reinforced magnesium composite were characterized using optical microscopy, transmission electron microscopy and X-ray diffraction. It was found that the Mg2B2O5 whiskers have a twinned structure with the (2 0 2) as the twin plane and growth direction along [0 1 0]. The MgB4O7 particles and the globular Mg2Si particles were observed within the Mg2B2O5 whisker, and at the interface between the Mg2B2O5 whiskers and Mg matrix, respectively. The MgO and MgB2 phase formed at the matrix–whisker interface during vacuum-gas pressure infiltration process due to the interfacial reaction. The crystallographic orientation relationships between the Mg2B2O5 whisker and the interfacial reaction products were found to be [010]Mg2B2O5//[1 1 0]MgO and [1 1 0]MgO//[21¯1¯0]MgB2, and (202)Mg2B2O5//(0 0 2)MgO and (0 0 2)MgO//(0001)MgB2, respectively. The factors that influence the microstructure of the Mg2B2O5 whiskers and the formation of the interfacial reaction products of Mg2Si, MgO and MgB2 phases were discussed.