Use of Laser Irradiation to Form Anti-Corrosive Surface Oxide Layer on Mg Metal

Abstract

Laser irradiation was used to improve the poor corrosion resistance of commercial grade pure magnesium (99.9 mass%) metal. The magnesium metal plates were immersed in a saturated Mg(OH)₂ aqueous solution and the hydroxide layer formed on the plates was decomposed by laser-irradiation in air to form a uniform anti-corrosive oxide layer. Light scanning confocal microscopy (LSCM) was used to measure the thickness of the oxide layer and characterize the surface morphology of the laser-irradiated specimens. Corrosion resistance of the laser-irradiated specimens was evaluated by the method of hydrogen evolution during immersion using a 1 mass% NaCl aqueous solution. This study revealed that low speed-scanning with a low heat-input laser formed a thick, uniform MgO layer by decomposition of the Mg(OH)₂ formed by primary immersion. The MgO layer prevented filiform corrosion and improved corrosion resistance of Mg metal.