Solid Solution Decomposition of Aluminum-Rich Aluminum-Zinc-Silver Alloys

Abstract

AbstractSolid solution decomposition of several aluminumrich aluminum-zinc-silver alloys were investigated using x-ray small angle scattering, x-ray diffraction (Guinier and Dewolff camera) and transmission electron microscopy. A decomposition sequence was observed directly fay means of hot stage electron microscopy, to be:G. P. zone → ɛ' → ɛG.P. zones were observed to exist in all of the ternary Al-Zn-Ag alloys used in this investigation. Only one type of G.P. zone was detected and evidence is given which indicated that the G.P. zone formation was governed by the existence of a metastable miscibility gap. Experimental results also indicated that the lattice of the matrix is distorted by the presence of the G.P. zone.A transition phase, designated ɛ', was observed to nucleate on defects in the matrix and to have a hexagonal close-packed structure. The ɛ' phase is partially coherent and much more regular in spatial distribution than the equilibrium ɛ phase.