Mechanical and chemical properties of organic coatings applied to metallic sheet substrates

Abstract

The mechanical properties of organic coatings of epoxy resin (DGEBA DER 332) and two diamine co-monomers (IPD and 3DCM) were measured and compared to bulk values. The coatings were deposited on aluminium and titanium alloy substrates. Differential scanning calorimetry (DSC) and near infrared spectroscopy (NIRS) were used to study the extent of reactions as a function of coating thickness for the two substrate alloys and compared to the bulk extent of reactions. Residual stress and Young’s modulus of the coatings were calculated using a one-dimensional analysis based on beam theory where the bi-axial modulus for isotropic stress was introduced (thin plate theory). As the strain in the coating causes strain in the substrate, which in turn produces in-plane deformation, the stiffness ratio was introduced. The Young's modulus and internal residual stress of the coatings were found to be dependent on the coating thickness, the extent of reaction and the substrate material. Curing agent loss was observed during the polymerisation thermal cycle and thus coating the extent of reaction evolution. The results showed that properties such as Young's modulus and stress are quite different between bulk and thin coatings.