Identification of β phase particles in an isothermally aged Al-10 mass%Mg-0.5 mass%Ag alloy

The structure and morphology of coarse-scale globular and smaller spheroidal particles in an isothermally aged Al-10Mg-0.5Ag (mass%) alloy have been charcterised by means of transmission electron microscopy. Coarse-scale globular and smaller spheroidal particles were commonly observed in an over-aged sample aged for 72 h at 240 degrees C. The coarse-scale globular and smaller spheroidal particles were identified by electron microdiffraction to have the face-centered cubic structure of equilibrium beta phase (Al3Mg2) (lattice parameter a = 2.824nm). The orientation relationship between the beta phase and alpha-Al matrix was such that: (100)(beta)//(100)(alpha) and [001](beta)//[001]. This orientation relationship differs from those reported previously for the beta phase formed in binary Al-Mg alloys. The coarse-scale globular beta particles had invariably internal faulted structures.