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

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. (C) 2019 Elsevier B.V. All rights reserved.