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.

The layers near the interface of explosively welded plates were investigated by means of microscopic observations with the use of transmission electron microscopy (TEM) equipped with energy dispersive spectrometry and scanning electron microscopy equipped with electron backscattered diffraction facility (SEM/EBSD). The metal compositions based on carbon or stainless steels (base plate) and Ti, Zr and Ta (flyer plate) were analyzed. The study was focused on the possible interdiffusion across the interface and the changes in the dislocation structure of bonded plates in the layers near-the-interface.It was found that the extremely rapid temperature increase followed by high cooling rates in the areas near the interface favour the formation of metastable phases. The crystalline or glassy nature of the phases formed inside melted zones strongly depends on the chemical composition of bonded metals. The amorphous phases dominates the melted zone of the (carbon or stainless steel)/Zr whereas the mixture of amorphous phases and nano- grains were identified in (carbon steel)/Ti and (stainless steel)/Ta clads. The elongated shape of the (sub)grains and the randomly distributed dislocations inside them as well as the shear bands and twins observed in the layers near-the-interface of all investigated clads, clearly indicated that during explosive welding, the deformation processes were prevailing over the softening ones.

The effect of interfacial microstructure on the electro-mechanical properties of explosively welded titanium and copper plates is discussed. Mechanical testing proved that using detonation velocities ranging from 2000 to 3000 m s⁻¹and stand-off distances from 1.5 to 9.0 mm, joints that satisfy the strength criteria for a good quality clad were produced. Scanning electron microscopy images show that all interfaces exhibit a wave character. It was noticed that as the stand-off distances and detonation velocities increase, the amplitude and period of the waves, as well as the quantity of the melt zones, increase as well. Also, as the interface waviness and volume fraction of the melt zones increase, the resistivity increases substantially. The experimental data demonstrate that the bonding between both metals is always achieved by surface melting of several tenths of a nanometer, which can be detected only by transmission electron microscopy. Most of the phases that form within the melt zones do not appear in the equilibrium phase diagram and show an amorphous/nano-grained structure. Only a very small amount of equilibrium phases such as CuTi₃, Cu₃Ti, Cu₄Ti₃was revealed employing synchrotron X-ray diffraction.