Effect of spraying distance and arc current on the corrosion behavior of arc-sprayed Zn–15Al coatings for rolling stock components

Arc sprayed Zn15Al coatings with different spraying parameters: arc current and spraying distance were investigated. The corrosion behavior of the coatings was studied using an electrochemical impedance spectroscopy (EIS), cyclic corrosion testing (CCT-4), and coastal railway exposure test. Corroded surfaces were characterized by scanning electron microscopy (SEM). The corrosion product formed on the coating was analyzed by X-ray diffraction (XRD) and scanning electron microscopy. From the potentiodynamic polarization test, the corrosion rate of the coating, using arc current of 100 A and a spraying distance of 100 mm, was 0.012 mm/year. The corrosion rate increased with increasing arc current and spraying distance. The corrosion mechanism of Zn15Al coating started with selective dissolution of Zn-rich phase leaving behind the passivated Al-rich phase and followed by stable corrosion product formation. From the surfaces analysis after the corrosion test, Simonkolleite (Zn 5 (OH) 8 Cl 2 •H 2 O) was found on the coating surfaces. Similarly, the samples exposed on the coastal railway line revealed Zn-rich phase dissolution and Al-rich phase passivation, but without protective corrosion product formations. Based on the corrosion rates, the results from the coastal railway exposure agreed well with electrochemical impedance measurement and cyclic corrosion test. Suggested spraying parameters for onsite repair was 100 A arc current and 100 mm spraying distance to achieve the optimal corrosion resistance of Zn15Al coating.