Influence of Zn and Mg Alloying on the Corrosion Resistance Properties of Al Coating Applied by Arc Thermal Spray Process in Simulated Weather Solution

Abstract

In this study, Al-Zn and Al-Mg coatings were deposited on steel substrates by an arc thermal spray process. X-ray diffraction and scanning electron microscopy were used to characterize the deposited coatings and corrosion products. Open circuit potential (OCP), electrochemical impedance spectroscopy, and potentiodynamic studies were used to assess the corrosion characteristics of these coatings after exposure according to the Society of Automotive Engineers (SAE) J2334 solution of varying durations. This solution simulates an industrial environment and contains chloride and carbonate ions that induce corrosion of the deposited coatings. However, the Al-Mg alloy coating maintained an OCP of approximately -0.911 V versus Ag/AgCl in the SAE J2334 solution even after 792 h of exposure. This indicates that it protects the steel sacrificially, whereas the Al-Zn coating provides only barrier-type protection through the deposition of corrosion products. The Al-Mg coating acts as a self-healing coating and provides protection by forming Mg6Al2(OH)(16)CO3 (Al-Mg layered double hydroxides). Mg6Al2(OH)(16)CO3 has interlocking characteristics with a morphology of plate-like nanostructures and an ion-exchange ability that can improve the corrosion resistance properties of the coating. The presence of Zn in the corrosion products of the Al-Zn coating allows dissolution, but, at the same time, Zn-5(OH)(6)(CO3)(2) and Zn6Al2(OH)(16)CO3 are formed and act to reduce the corrosion rate.