Microstructure and interface characterization of a cast Mg_2B_2O_5 whisker reinforced AZ91D magnesium alloy composite

摘要

In this study, the microstructure and interface of a Mg_2B_2O_5 whisker-reinforced magnesium composite were characterized using optical microscopy, transmission electron microscopy and X-ray diffraction. It was found that the Mg_2B_2O_5 whiskers have a twinned structure with the (2 0 2) as the twin plane and growth direction along [0 1 0). The MgB_4O_7 particles and the globular Mg_2Si particles were observed within the Mg_2B_2O_5 whisker, and at the interface between the Mg_2B_2O_5 whiskers and Mg matrix, respectively. The MgO and MgB_2 phase formed at the matrix-whisker interface during vacuum-gas pressure infiltration process due to the interfacial reaction. The crystallographic orientation relationships between the Mg_2B_2O_5 whisker and the interfacial reaction products were found to be [010]_(Mg_2B_2O_5)//[1 1 0]_(Mgo) and [1 1 0]_(Mgo)//[2110]_(MgB_2), and (202)_(Mg_2B_2O_5)//(0 0 2)_(Mgo) and (00 2)_(Mgo)//(0001)_(MgB_2), respectively.The factors that influence the microstructure of the Mg_2B_2O_5 whiskers and the formation of the interfacial reaction products of Mg_2Si, MgO and MgB_2 phases were discussed.