| Traditional solvent-based epoxy zinc-rich coating has been widely used in industrial production because of its excellent corrosion resistance and sacrificial protection features. However, the zinc content of zinc-rich epoxy coating is too high, which could easily lead to the "Zinc fever" in production operations. In addition, as the social environmental consciousness gradually increased and the relevant regulations and standards introduced, the use of organic solvents has been given more and more restrictions. The waterborne epoxy coating becomes an inevitable trend for the development, but the corrosion resistance of water-based paint needs to be further improved.This paper substituted the zinc-aluminum alloy powder for traditional zinc powder to reduce the amount of metal powders and modified the epoxy resin to reduce the ues of organic solvents. The experiments in this paper were based on the study of epoxy zinc-rich coating and chrome-free zinc-aluminum coating. The roughly content of each component in waterborne epoxy Zn-Al coating was determined by single factor tests. Then factor 5 level 4 experiment was designed, and the ideal formula was determined accoding to the evaluation of the appearance, adhesion and corrosion resistance. Finally, the analysis of SEM, EDS, XRD and other testing methods were applied to study the morphology and composition of the coatings as well as the adhesion, hardness and corrosion resistance. The results showed that the ideal formula of the waterborne epoxy zinc-aluminum coating is(mass percentage), 30.5% zinc aluminum powder, 11% wates-borne epoxy resin, 19.5% curing agent, 4% dispersant, 7% organic solvents, 1-2% defoamers and other additives, and the balance was distilled water. The surface morphology of coating was layered structure consisted of Zn-Al alloy pigments. The thickness of the coating was about 25?m and the coating was well bonded to the substrate. The corrosion potential and corrosion current of the coating in 3.5% NaCl solution were-0.944 V and 1.829 × 10-7 A?cm-2 respectivelly. The coating remained no red rust for 45 days in 5% NaCl neutral salt spray test.In order to further improve the corrosion resistance of water-based epoxy zinc-aluminum coating, we modified ZrO2 nanoparticles by silane coupling agent KH550 and then prepared nanocomposite zinc-aluminum coating by adding the ZrO2 nanoparticles. The preferable conditions of the surface modification of ZrO2 nanoparticle were hydrolysis for 60 min under p H value 6 with 5% KH550. The optimal dosage of ZrO2 nanoparticles was 1.5%. The surface hardness of the coating increased by 16.9% and the friction coefficient decreased, which implied the wear resistance increased after adding ZrO2 nanoparticles. Besides, the water absorption decreased and the water resistance improved significantly as well as acid-base resistance property.In the 3.5% Na Cl solution, the corrosion current was 1.094 × 10-8 A ? cm-2, which reduced by oneorder of magnitude. The nanocomposite zinc-aluminum coating remained no red rust and generated only a small amount of white rust after 65 days neutral salt spray test. The impedance of the coating was 108 orders of magnitude, which implyed the good physical shielding property. |
PDF Full Text Request