Orientation Relationships and Interface Structure in MgAl2O4 and MgAlB4 Co-Reinforced Al Matrix Composites.

Ceramic phase reinforced aluminum matrix composites (CAMCs) are widely used in high-tech fields represented by aerospace industry due to their advantages of high specific strength, high specific modulus, high thermal stability, and light weight. Strong interface bonding is a prerequisite for high performance of multiphase materials. Herein, a novel CAMC in situ reinforced by MgAl2O4 particles and MgAlB4 nanorods was prepared by vacuum hot-pressing combined with hot-extrusion process. A high-resolution transmission electron microscope was used to characterize the orientation relationship and interface structure between the ceramic phases and the aluminum matrix. Two orientation relationships (OR1 and OR2) of MgAl2O4/Al and one (OR3) of MgAlB4/Al are determined: OR1-[011]p//[011]Al, (11̅1)p//(11̅1)Al; OR2-[211]p//[011]Al, (113̅)p//(022̅)Al; OR3-[101̅0]R//[001]Al, (0002)R//(2̅20)Al. The MgAl2O4 in OR1 forms a coherent interface with the aluminum matrix at (111) surface, while they form a 4 × 5 near coincidence site lattice (CSL) interface structure for OR2. In OR3, the MgAlB4 forms an approximate coherent interface with Al matrix at its (0002) surface and a 2 × 5 CSL interface structure at its (011̅0) surface. First-principles calculations suggest that MgAl2O4 combines to aluminum at (111) plane through covalent bonds, which means high interfacial bonding strength. The hot-extrusion process makes the ceramic phase evenly distributed in the matrix. The mechanical properties of the composites are greatly improved compared with pure aluminum.