3.4. Cathodic disbonding measurements
Cathodic delamination of the epoxy coatings applied on the
steel substrates without and with phosphate conversion coatings
was studied. The disbonded radiuses of different samples were
obtained after 100 h cathodic disbonding test and the results are
given in Fig. 7.
According to the results given in Fig. 7, the coatings applied on
the surface treated substrates showed lower disbonded radius than
bare steel substrate. Also, it can be seen that the lowest disbonding
radius was obtained for the coating applied on the sample treated
by Zn-PVA. This observation demonstrates that PVA could effectively
reduce the epoxy coating disbondment on the phosphated
steel substrate. These can be attributed to the stronger adhesion
bonds that the epoxy coating produced with the steel substrate
treated by Zn-PVA. Also, the decrease in cathodic activity of the
metal substrate after treatment with Zn-PVA cause the decrease
in cathodic activity of the metal substrate, leading to the decrease
in the rate of hydroxyl ions creation in the hole and beneath the