In–situ synthesis of an Al–based composite reinforced with nanometric γ–Al₂O₃ and submicron AlB₂ particles

In this study, an Al–based composite reinforced with nanometric γ–Al₂O₃ and submicron AlB₂ particles was fabricated via chemical reactions between Al and boron oxide, followed by hot extrusion. The volume fraction of in–situ formed γ–Al₂O₃ and AlB₂ is 11.2 vol% and 6.3 vol%, respectively. The average size of γ–Al₂O₃ and AlB₂ is around 50 nm and 500 nm, respectively, and the α–Al grain is 1.26 µm in the longitudinal section. The γ–Al₂O₃ particles either distribute inside of α–Al grains or exhibit particle chains or networks locating along grain boundaries, while AlB₂ particles are uniformly distributed among the matrix grains. The Young's modulus is averaged at 91 GPa, and the ultimate tensile strength and elongation of the composite at room temperature are averaged to be 426 MPa and 8.1 %, respectively. The yield strength at 350 °C is as high as 217 MPa. It is regarded that the relatively fine α–Al grains along with the γ–Al₂O₃ particles inside of α–Al grains and AlB₂ particles are mainly responsible for room temperature strengthening, while the γ–Al₂O₃ particle chains or networks along grain boundaries play the key role in grain boundary strengthening at 350 °C. This work may provide new insights for designing and fabricating Al–based composite for elevated–temperature application.