Microstructure and corrosion behaviour of arc sprayed Zn–Al–Mg–RE cathodic protection coatings on steel substrates

Cored wires and high velocity arc spraying technologies have been used to produce Zn–Al–Mg and Zn–Al–Mg–RE (where RE is rare earth) coatings on A3 steel. The durability of coatings in terms of corrosion resistance is the focus of this paper. To study the effect of RE, Zn–Al–Mg coatings also have been produced as a comparison. The microstructures of original coatings and corroded coatings have been investigated after corrosion tests by SEM and XRD. The potentiodynamic polarisation and electrochemical impedance spectroscopy techniques were carried out to determine the corrosion behaviour of the two coatings in 5% NaCl solution. Metallographic as well as electrochemical corrosion results illustrate that the coatings possess a self-sealing capacity, and that the corrosion products can refine the microstructure and enhance the corrosion resistance. Compared to the Zn–Al–Mg coating, the Zn–Al–Mg–RE coating presents a more obvious and stable self-sealing process.