The mechanism and kinetics of Al3Li/Al3Sc composite particles formation during aging of triple AlLiSc alloys were studied. The particles of such type consist of two isomorphic phases, ordered by L12 type. Composite particles in AlLiSc are formed by epitaxial nucleation of δ (Al3Li) phase on pre-existing Al3Sc precipitates at low temperature aging in the area of existence of Al3Li phase, and form uniform shell around them. The motive force of such heterostructure formation is the minimization of total surface, elastic and chemical energy of the alloy. Dark-eld transmission electron microscopy images of such composite particles taken from superlattice reex 100 are composed of a dark core surrounded by a bright shell. The mutual diusion of Li and Sc during the aging of AlLiSc alloys is observed. The dark-eld transmission electron microscopy image of the composite particle obtained from superlattice reection became transparent after continuous natural aging of AlLiSc alloys. The presence of the particle in Al matrix can be only seen due to decoration by secondary precipitations of δ (Al3Li) phase. Composition analysis of such transparent particles was carried out using two-beam kinematical theory of electron diraction. Such composite particles with transparent cores remain in Al matrix even after severe plastic deformation of AlLiSc alloy.

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