Study On The Preparation Of Arc Sprayed Al-Zn-Si Alloy Coatings And Their Corrosion Resistance In Marine Environment

Zn-Al coatings are replacing the traditional pure Zn or Al coatings in the field of long life anti-corrosion for large steel constructions. Therefore, it is very important to study the preparation and corrosion resistance of Zn-Al coatings with high corrosion performance.In this paper, arc spraying technology was used to prepare Al-Zn-Si alloy coating and Al-Zn pseudo-alloy coating with the same Al content. The parameters were optimized through the Orthogonal test. The specimens with scratch route were used to accelerate the corrosion tests. Comparative studies on the corrosion products and electrochemical measurements were investigated to evaluate the corrosion resistance of the two coatings exposed in three kinds of simulated marine environments, including salt water immersion test and neutral salt spray test. X-ray diffraction technique(XRD), optical microscope(OM) and scanning electron microscope(SEM) were employed to study the microstructure and the composition of the corrosion products. Electrochemical measurement techniques were carried out by Tafel and EIS. Hole sealing treatment was also used to evaluate the change of the corrosion resistance. Furthermore, the corrosion mechanisms of Al-Zn-Si alloy coating in different environments were discussed.The results showed that the best arc spraying parameters on the performance of the Al-Zn-Si alloy coating is spraying voltage 28 V, spraying current 180 A, spraying distance 150 mm, spraying pressure 0.6 MPa. The components of Al-Zn-Si alloy coating were more uniform than that of Al-Zn pseudo-alloy coating. Al-Zn pseudo-alloy coating was corroded more seriously than Al-Zn-Si alloy coating after immersed in salt water for 150 d and exposed to neutral salt spray testing for 60 d.The scratches on the coatings were self-repairing well. Hole sealing treatment relieved the corrosion damage. The corrosion current densities of Al-Zn-Si alloy coating and Al-Zn pseudo-alloy coating were 2.482 ×10-5 A·cm-2 and 5.901×10-5 A·cm-2. The corrosion current densities of the two coatings after hole sealing treatment were 1.3×10-5 A·cm-2 and 1.35×10-5 A·cm-2 respectively. The impedance value of Al-Zn-Si alloy coating after hole sealing treatment increased. The corrosion products of Al-Zn-Si alloy coating were mainly Basic Zinc Chloride, Zinc aluminum carbonate hydroxide hydrates and Hydroxy aluminium chloride hydrate.