Application of phosphonic acids on plasma activated zinc alloys surfaces for improved corrosion and adhesion properties

摘要

Alloy coated steel is one of the main raw materials of automobile, appliance and construction industries. Binary or ternary mixtures of zinc, aluminium and magnesium are the most frequently used alloy coatings to increase the corrosion resistance of steel. In most cases the steel sheets are additionally coated with polymeric layers like paints or adhesives. To realise the ultimate aim, the design of high corrosion resistance and adhesion strength materials, it is necessary to understand the chemistry of the alloy surface and the fundamental processes occurring at the organic coating - alloy interface in presence of corrosive electrolytes. In this paper we are presenting investigastions of the adsorption and water resistance of organic phosphonic acids on plasma modified Zn-Mg-AI alloy surfaces based on complementary microscopic and spectroscopic measurements, plasma modifications were carried out by means of the strip hollow cathode (SHC) method with specific regard to a high modification intensity. The influence of different plasma modifications on corrosion resistance was shown in electrochemical investigations. The parameters of plasma modifications were correlated to the properties of treated surfaces by means of optical and electronic spectroscopy. Phosphonic acid has been deposited on the Zn-Mg-AI alloy surfaces before and after plasma modification. By means of polarization modulation infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy (PM-IRRAS and XPS) the adsorption and self-organization of monofunctional monolayers were analysed. Both the plasma modification and the SAM adsorption cause an improved corrosion resistance of the Zn-Mg-AI alloys. The best corrosion protection was observed after Ar/H2 with subsequent O_2 plasma treatment.