Initial Stage of Localized Corrosion of Al-9 mass% Si Coated Steels after Removal with a Photon Rupture Method in Solutions

Abstract

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 SO₄^2- 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.