RIASSUNTO
Abstract
The multifunctional composite coatings having practically important properties (anticorrosive, antifriction, hydrophobic, superhydrophobic etc.) were obtained on the aluminum and magnesium alloys using plasma electrolytic oxidation (PEO) and fluoropolymer materials (superdispersed polytetrafluoroethylene powder, tetrafluoroethylene telomeric dispersions) and compounds on the base of hydrophobic agent as well. The embedding of nanosized polymer compounds into the coatings compositions allows increasing their stability in corrosive media. Furthermore, the composite coating is characterized by practically important antifriction properties due to low friction coefficient. Polymer-containing coatings decrease the corrosion current density and wear by 6 and 4 orders of magnitude, respectively, as compared to unprotected alloys. The formation methods of hydrophobic (HP) and superhydrophobic (SHP) nanocomposite coatings on the surface of alloys pretreated using PEO were developed also.
Introduction
Today aluminum and magnesium alloys are used increasingly in industries such as aviation, automotive, production of high-tech devices and in the associated components. But low corrosion and wear resistance substantially restrict the application of these promising materials in marine applications. One of possible ways to protect aluminum and magnesium alloys from the negative impact of corrosion media and friction is the fabrication of coatings by plasma electrolytic oxidation (PEO) (Nĕmcová et al. 2014; Dunleavy et al. 2013; Gnedenkov et al., 2013). Coatings formed by PEO have a number of useful characteristics, such as corrosion and wear resistance, thermal stability, high adhesion to the substrate, etc. (Hussein et al. 2013; Gnedenkov et al. 2001). PEO-method allows forming on the magnesium alloy protective layers, which have a convolute, rough surface also (Cheng et al. 2013; Sinebryukhov et al. 2010; Lee et al. 2014). Such structure can be used as a base for application on the PEO pretreated surface with the polymeric materials in order to provide the additional protection for the processed alloys and metals. Thereupon fluoropolymers present the particular interest due to their chemical and thermal stability. A composite coatings obtained by using superdispersed polytetrafluoroethylene were formed (Zhang et al. 2013; Wang et al. 2010; Gnedenkov et al. 2014). These coatings showed higher protective properties as compared to the base PEO-layers. This article presents the results of investigation of protective properties of composite coatings (CC) obtained on magnesium and aluminum alloys with using of various organofluorine materials: superdispersed polytetrafluoroethylene (SPTFE), tetrafluoroethylene telomers and on the base of hydrophobic agent.