Electrodeposition of Zn-Ni/PTFE composite coating on 20 steel and its corrosion behavior in simulated sewage

Abstract

Zn-Ni alloy coating was electrodeposited on 20 steel, which was commonly used in the manufacture of pipes and connectors. Polytetrafluoroethylene (PTFE) is a kind of polymer chemical material. Although many researchers have prepared metal composite coatings with decent corrosion resistance by adding PTFE particles to the plating solution, a large number of PTFE particles are easy to agglomerate in aqueous solutions, which affects the compactness and properties of composite coatings. In this paper, by adding PTFE emulsion to Zn-Ni plating solution, the agglomeration phenomenon of PTFE particles can be effectively reduced to improve the content of PTFE particles in Zn-Ni/PTFE composite coating and enhance corrosion resistance, which has certain innovation and significance. The surface morphology, chemical composition and phase structure of Zn-Ni alloy coating and Zn-Ni/PTFE composite coatings were characterized and analyzed by scanning electron microscopy, energy dispersive spectrometer and X-ray diffraction. Moreover, the bonding strength and thickness of Zn-Ni alloy coating and Zn-Ni/PTFE composite coatings were tested by grid testing and step profiler. The results show that PTFE particles incorporate into the coating and play a role in increasing the corrosion resistance of the composite coating in simulated sewage. However, the incorporated PTFE particles have no obvious effect on the phase structure of the composite coating. When the addition amount of PTFE emulsion is 30 mL/L, the electrodeposited Zn-Ni/PTFE composite coating has the highest content of PTFE particles (4.24 %), and the corrosion current density is only 0.90 μA/cm2, which is nearly two orders of magnitude lower than that of 20 steel. The Zn-Ni/PTFE composite coating electrodeposited from the plating solution containing 30 mL/L PTFE emulsion has the lightest corrosion degree in simulated sewage and shows excellent corrosion resistance, which can effectively delay the corrosion of 20 steel.