A photon rupture technique was used to investigate abrupt destruction and repair of passive oxide films on A-9 mass% Si coated steels. Specimens covered by anodic oxide films were irradiated with a focused pulse of a pulsed Nd-YAG laser beam at a constant potential in 0.1kmol/m3 Na2B4O7, pH=9.2, with and without Cl-and SO42-ions while monitoring the current transients. Irradiation with a focused pulse of a pulsed laser beam in the solutions causes abrupt removal of the anodic oxide film at the irradiated area. Without aggressive anions and also with aggressive anions at low potential, oxide films were reformed after the laser irradiation. With increasing the potential, the current increased in the solutions with aggressive anions. This behavior can be explained by a preferential dissolution of the metal substrate, which is enhanced at higher potentials. It may be concluded that localized corrosion of Al-Si coated layers occurs at high potentials while film repair occurs at low potentials in solutions with aggressive anions.

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A photon rupture method, film removal by a focused pulse of pulsed Nd-YAG laser beam irradiation, has been developed as it enables oxide film stripping at extremely high rates without contamination from the film removal tools. In the present study, Zn and Zn-5mass%Al alloy coated steel specimens covered with protective nitrocellulose film were irradiated with a focused pulse of a pulsed Nd-YAG laser beam at a constant potential in 0.5 kmol m Ϫ3 H 3 BO 3 -0.05 kmol m Ϫ3 Na 2 B 4 O 7 (pHϭ7.4) with/without 0.05 kmol m Ϫ3 of chloride ions to investigate the initial stage of localized corrosion. At low potentials, both samples reformed oxide film after the nitrocellulose films were removed by this method. The oxide film formation kinetics of Zn-55mass%Al follow an inverse logarithmic law, in agreement with Cabrera-Mott theory. However, at high potentials, localized corrosion producing corrosion products occured at the area where nitrocellulose film was removed. The dissolution current of the Zn coated steel samples is higher than that of Zn-5mass%Al coated samples at the same applied potential.

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