Abstract
Interfacial layers have been detected in bonds formed between hot dip galvanised steel substrates and heat cured epoxy adhesive. The layers have a number of features which affect the impact performance of the bonds formed compared with the equivalent bonds with mild steel substrates. The mechanical properties of the interfacial layers have been found to be significantly different to that of the bulk adhesive. Analysis of the layers showed an absence of silicate filler particles within the layers. Bubbles were also found at the surface of the hot dip galvanised substrates as a byproduct of a chemical reaction, which may occur between the hardener in the adhesive and the substrate surface. Pyrolysis experiments showed that a gas was produced when zinc–dicyandiamide mixtures are heated at the adhesive cure temperature. The production of interfacial layers has also been found to be strongly dependent on subtle changes in the surface chemistry or structure of the substrates.
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