Comparison of the failure mechanisms of silicone-epoxy hybrid coatings on type A3 mild steel and 2024 Al-alloy

Comparison of failure mechanisms of silicone-epoxy hybrid coatings on mild steel and Al-alloy immersed in 5 wt.% NaCl solution was studied by electrochemical impedance spectroscopy, pull-off tests, differential scanning calorimetry and ultra-depth three-dimensional microscope. The results show that there were the effects on diffusion behavior in middle immersion and oxide film formed on metals in final immersion for mild steel and Al-alloy substrates. The effect of coating thickness on the cross-linking density of silicone-epoxy polymer was obvious. The delaminated area and the roughness of coating/metal interfaces were discussed from their respective break-point frequency and fractal dimensions deduced from impedance measurements.