On the thermal stability of coating in an Al18B4O33w/α-Al2O3/6061Al composite

A sol–gel α-Al2O3 coating was deposited on aluminum borate whiskers to restrain the interfacial reaction occurring in a 6061Al matrix composite. The fine structure of the interface in the coated composite was characterized by electron microscopy. Experimental results showed that, even after thermal exposure at temperatures up to 550 °C, the nanocrystalline α-Al2O3 coating was effective in hindering the interfacial reaction between the whisker and the matrix and preserving the tensile strength of the composite. But the coating dissolved and thus lost its protective role after thermal exposure at 800 °C. This may be due to extensive diffusion of elements at the whisker/liquidus matrix interface.