1 Mackay icosahedron explaining orientation relationship of dispersoids in Al alloys Astrid Marie F. Muggerud a* , Yanjun Li b , Randi Holmestad a and Sigmund J. Andersen c a Department of Physics, Norwegian University of Science and Technology, NTNU, N-7491 Trondheim, Norway. b Department of Materials Science and Engineering, University of Science and Technology, NTNU, N-7491 Trondheim, Norway. c SINTEF Materials and Chemistry, NO-7465 Trondheim, Norway. * Correspondig author. Tel. +47 73593435. E-mail adress: astrid.muggerud@ntnu.no. Keywords: Aluminum; Homogenization; Dispersoids; Orientation relationship; Transmission electron microscopy (TEM). Abstract The orientation relations (ORs) of the cubic icosahedral quasicrystal approximation phase α- Al(Fe,Mn)Si have been studied after low temperature annealing of a 3xxx wrought aluminum alloy by transmission electron microscopy. From diffraction studies it was verified that the most commonly observed OR for the α-Al(Fe,Mn)Si dispersoids is 1 11 [ ] α // 111 [ ] Al, 527 ( ) α // 011 ( ) Al. This orientation could be explained by assuming that the Mackay icosahedron (MI) internal in the α-phase has a fixed orientation in relation to Al, similar to that of the icosahedral quasi-crystals existing in this alloy system. It is shown that mirroring of the MI normal to high symmetry icosahedral directions explains alternative orientations, which are therefore likely to be caused by twinning of the fixed MI. Only one exception was found, which was related to the MI of the T-phase in Al-Mg-Zn. *Text only Click here to download Text only: Paper_OR_ready.doc Click here to view linked References