Salt Spray Corrosion Resistance of Aluminized Coatings on X70 Pipeline Steel by Laser Thermal Radiation

Abstract

The surface of X70 pipeline steel was aluminized by laser thermal radiation, the surface and interface morphologies of aluminized coatings were observed by SEM (scanning electron microscope), and energy spectrum of chemical elements in the bonding interface were analyzed by EDS (energy dispersive spectrometer). The element-distributions in the bonding interface before and after salt spray corrosion (SSC) were studied with plane scanning analysis, the phases of aluminized coating surface before and after SSC were analyzed with XRD (X-ray Diffractomer), and the effects of the aluminized coating on the SSC resistance of X70 pipeline steel were researched. The results show that the oxide aluminum coating is formed on X70 pipeline steel surface by laser thermal radiation, and the distributions of chemical elements are uniform, which are inter-infiltrated between the aluminized coating and the substrate resulting in forming metallurgical bonding. The pitting corrosion is relatively serious on the surface of X70 pipeline steel after SSC, and then the general corrosion is formed. The compact protection film of Al2O3 is generated on the sample surface after laser thermal radiation, which prevents from the contacting between corrosive medium Cl− and active Fe atom of the substrate, so as to improve the ability of SSC resistance of X70 pipeline steel.