Precipitates formed by aging in deformed Al-Mg2Si alloys were classified using high resolution transmission electron microscopy (HRTEM) in order to understand the effect of excess silicon contents and deformation on precipitation. Two types of precipitates appeared on the dislocation in the deformed Al-Mg2Si alloy including 0.4mass% silicon in excess (excess Si alloy) at early stage during aging at 473K. First one is the string-like precipitate that consisted of a lot of small precipitates linked as a string-beads along the dislocation line. Second one is the elongated type precipitate that is the end-on of the needle- or rod-shaped precipitate having the elongated cross section. There were a lot of the TYPE-C precipitates on the dislocation after a peak aging. There were the random type precipitates and β" phase in the matrix which were independent on the existence of the dislocation. At the early stage during aging, a lot of the random type precipitates appeared in the matrix. Next, the β" phase appeared and the coarse TYPE-A precipitates finally appeared at the over aged condition. It has been clarified in our recent work that the β" phase, the TYPE-A and the TYPE-C precipitates are typical precipitates in the excess Si alloy. It was considered that the string-like precipitate grows to the elongated-type precipitate and then those transforms to the TYPE-C precipitate with progress of aging, because there is similarity of the arrangement of bright dots and orientation relationship in their HRTEM images between the string-like and elongated-type precipitates, and the TYPE-C precipitate. The β' phase increased and the TYPE-C precipitate decreased on the dislocation in the over aged alloy with decreasing of excess silicon contents. There were no TYPE-C precipitates and the β' phase predominantly appeared on the dislocation in the over aged alloy without excess silicon contents. It was found that the TYPE-C precipitate is a typical precipitate which appears inhomogeneously in the deformed excess Si alloy.
