Aimed to control the interfacial reaction in Al18B4O33/Al composites, the artificial nitridation process is proposed based on thermodynamic calculations, which leads to a 50-nm thick artificial nitrided coating surrounding a Al18B4O33 whisker. Aluminum (AC8A) matrix composites reinforced with different Al18B4O33 whiskers were processed and Al18B4O33 whiskers were used in their as-received form and after artificial nitridation. The interface region between the aluminum matrix and Al18B4O33 was charactered using transmission electron microscopy. Results show that extensive reaction takes place during the incorporation process between the as-received Al18B4O33 whiskers and the aluminum matrix and Mg in the base alloy forms MgAl2O4 spinel phases. Such interfacial reaction is enhanced after T6 heat treatment. In the case of artificially nitrided Al18B4O33 whiskers, even though the artificial nitrided coating surrounds the Al18B4O33 whisker, it can react with the AC8A alloy to produce MgAl2O4, but the degree of the interfacial reaction is reduced. The interfacial reaction only consumes the artificial nitrided coating instead of the reinforcement whiskers and the integrity of the whisker is preserved. (C) 2004 Kluwer Academic Publishers.