Microstructure and tensile properties of ZnO-coated magnesium borate whisker reinforced AZ31B composite

ZnO-coated Mg2B2O5 whisker was prepared by a sol–gel method and subsequently calcined at 450 °C in the air. AZ31B magnesium matrix composite reinforced by ZnO-coated Mg2B2O5 whiskers was fabricated via vacuum-gas pressure infiltration process. The effects of ZnO coating on the microstructure and mechanical properties of the composite were investigated and tensile tests were conducted at room temperature. The results indicate that the tensile strength of the ZnO-coated Mg2B2O5 whisker reinforced AZ31B composite increased from 181 MPa to 305 MPa and the elongation to fracture can reach 2.5% from 1.4%, compared with that of the uncoated Mg2B2O5 whisker reinforced AZ31B composite, respectively. Mg3B2O6 phase formed in the ZnO-coated Mg2B2O5 whisker calcinated 2 h at 450 °C and then sintered 2 h at 800 °C. During vacuum-gas pressure infiltration process, the MgO, Mg0.85Zn0.15O and MgZn2 phases formed at the matrix–whisker interface as a result of the interfacial reaction. The orientation relationship between MgZn2 and Mg2B2O5 is indexed to be [ 5 1 ¯ 4 ¯ 3 ] MgZn 2 / / [ 0   1   0 ] Mg 2 B 2 O 5 and ( 0   1 ¯   1   1 ) MgZn 2 / / ( 0   0   2 ) Mg 2 B 2 O 5 in a specific position. The mechanism of the effect of the ZnO coating on the interfacial microstructure and the tensile properties of the composite was discussed.