The thermal behaviour of metal Al and Al-(Mg,Si) alloys in N-2 has been examined by TG. Above 700 degrees C, the Al-(Mg,Si) alloys in N-2 can be directly converted to AlN/Al matrix composite. The reaction rate of the nitridation of Al-(Mg,Si) alloys is greatly influenced by the dopants Mg and Si, The reaction mechanism of nitridation established from the regression of g(alpha) under various conditions versus t seems to be one-dimensional diffusion.