Sol–gel alumina coatings for whisker reinforced metal matrix composites

There exist serious interfacial reactions in squeeze-casting aluminum borate whisker reinforced 6061Al composites. To control the spinel reactions a sol–gel coating method was used to deposit γ-Al2O3 and α-Al2O3 ceramic coatings on aluminum borate whiskers. TEM observations of coating morphology indicate that nanostructured alumina coatings are uniformly deposited on whisker surfaces, with a thickness of about 30–50 nm. Ball-milling has an important effect on final mechanical properties of the composites. γ-Al2O3 and α-Al2O3 coatings were found to be effective in controlling the interfacial reactions, by completely preventing the diffusion of magnesium from matrix/coating interface to coating/whisker interface.