The microstructure changes and the phase constitution within the layers close to the bonding interface strongly influence the properties of bimetallic strips. In this work, the layers near the interface of explosively welded aluminum and copper plates were investigated by means of microscopic observations, mostly with the use of transmission electron microscopy (TEM) equipped with energy dispersive spectrometry (EDX). The study was focused on the identification of the intermetallic phases, the possible interdiffusion between the copper and the aluminum, and the changes in the dislocation structure of the parent plates. In macro-/mesoscale, the interfaces were outlined by a characteristic sharp transition indicating that there was no mechanical mixing between the welded metals in the solid state. In micro-/nanoscale, the layers adhering to the interface show typical deformed microstructure features, i.e., structure refinement, elongated dislocation cells, slip bands, and microtwins (in copper plate). The internal microstructure of the intermetallic inclusion is composed mostly of dendrites. The electron diffractions and TEM/EDX chemical composition measurements revealed three crystalline equilibrium phases of the γ-Al₄Cu₉, η-AlCu, and Θ-Al₂Cu type (the last one was dominant). However, most of the observed phases of the general Cu _m Al _n type (also crystalline) do not appear in the equilibrium Al-Cu phase diagram. Inside the intermetallic inclusions, no significant regularity in the phase distribution with respect to the parent sheets was observed. Therefore, it was concluded that the processes occurring in the melt determined their local chemical composition.