The structural relation between precipitates in Al-Mg-Si alloys, the Al-matrix and diamond silicon, with emphasis on the trigonal phase U1-MgAl2Si2

Atomic structures of the precipitates in Al-Mg-Si alloys have important similarities. The trigonal precipitate U1-MgAl2Si2 has super-cells in both Al and diamond Si. U1 is related to the precipitates beta', U2, and beta' via silicon. The Si-content of the four precipitates can be described as triangular planes parallel to Al {100} or Al {310} planes. Large Si-particles frequently align two of their {111} planes in a similar way. In the Al-Mg-Si alloy system this correspondence explains most coherency relations between precipitates, and between precipitates and matrix. The connection with Si gives a unified view of the precipitate structures. A model is given for a reflection twin boundary in U1. (c) 2006 Elsevier B.V. All rights reserved.