Deposition of Zn-G/Al composite coating with excellent cathodic protection on low-carbon steel by low-pressure cold spraying

Abstract Zn–Al composite coating has a limited cathodic protection for low-carbon steel in harsh environment. The aim of this work is to uniformly disperse graphene (G) into Zn–Al composite coating to improve the cathodic protective ability of Zn–Al composite coating. The graphene was coated on Al powders by in-situ reduction, and then the G coated Al powders (G/Al) were co-deposited with Zn powders on low-carbon steel by low pressure cold sprayed (LPCS) method. The morphology, phase compositions of G/Al powders and the as-deposited Zn-G/Al coatings were analyzed by using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. Besides, the cathodic protection property of the coatings was evaluated based on the electrochemical behavior of the intact coatings and the self-healing behavior of the scratched coatings. The results revealed that G was uniformly distributed among Zn–Al interface. Electrochemical behavior of the intact coatings suggested that the Zn-G/Al composite coatings showed a lower self-corrosion potential with higher corrosion current than that of Zn–Al, which means the cathodic protection ability of Zn-G/Al coating was enhanced by the addition of G. Self-healing behavior of the scratched coating demonstrated that corrosion products of Zn-0.2 wt% G/Al coating is quickly formed and filled into scratch. According to the EIS results, the scratched Zn-0.2 wt% G/Al coating displayed the largest polarization resistance after 72 h of immersion in 3.5 wt% NaCl solution. The improved cathodic protection ability of Zn-G/Al coating can be attributed to the severe galvanic corrosion from the high conductivity of graphene in the coating.