Chemical conversion of zinc–zinc phosphate composite coating on TC4 by galvanic coupling
Abstract
Galvanic coupling approach was introduced into chemical conversion of zinc–zinc phosphate composite coatings on Ti-6Al-4V (TC4) to overcome their surface inertness. The phase composition, morphology, electrochemical performance and adhesive strength of the coating were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), electrochemical workstation system and scratch tester, respectively. The results showed that the uniform and fine zinc–zinc phosphate (Zn3(PO4)2·4H2O) composite coatings were prepared on TC4 by galvanic coupling with AZ91D magnesium alloy (MA). The area ratio of TC4 to MA being 1 : 1 in coupling pair presented better corrosion resistance. The scratch test revealed that the coating formed by galvanic coupling at the area ratio of 1 : 2 presented better adhesive strength between coating and substrate.