Interfaces in Al₁₈B₄O₃₃/Al, Mg alloy composites

Al₁₈B₄O₃₃ whisker reinforced Al, Mg alloy composites were prepared by a squeeze casting process. The interaction among the interface structure, heat stability and strength of the composites was analyzed. In the pure Al matrix composite, the interfacial reaction occurred only at a temperature higher than 750°C and its reaction products are γ-Al₂O₃. Interfaces between the whisker and reaction products have a preferred orientation with little mismatch. In the AC8A matrix composite, MgAl₂O₄ with a spinel structure was produced at the interface at a temperature higher than 500°C. These reaction products were shaped rectangularly. These reactions lead to the corrosion and shortening of the whiskers. It causes the degradation of the bending strength of the composites. In the AZ91D matrix composites, the reaction products are MgAl₂O₄ layers with a uniform thickness. This layer prevents the direct reaction between the whisker and the matrix. Consequently the whiskers are scarcely damaged and the composites have a good bending strength at high temperature.