Aging process of SiC particle dispersed Al–lmass%Mg2Si alloy composite materials was investigated by micro-Vickers hardness measurement and transmission electron microscope observation. In the SiC particle dispersed composite materials, preferential precipitates on dislocations which had been introduced during quenching after solid solution treatment are observed. The age hardenability slightly decreased as compared with that of the matrix alloy. At peak aged condition of composite materials, most of the precipitates have the structure that is characteristic by parallelogram shaped arrays of bright dots with the intervals of 0.77 and 0.67 nm. The arrays of bright dots of the precipitates also posses an adjacent interior angle of 75 degrees. At over aged conditions, one kind of intermediate precipitates, the type–C precipitate having the lattice parameter of a=1.04 nm and c=0.405 nm are observed at relatively higher frequencies corresponding to the tendency of the type–C precipitates to precipitate preferentially on the dislocation.
