| The corrosion of automobile metal parts will not only affect the performance and driving safety of the vehicle seriously,but also bring huge economic waste and environmental problems.Dacromet is mainly used in steel surface corrosion protection,it has a lot of characteristics including high corrosion resistance,high adhesion,and excellent weather resistance.Therefore,Dacormet has been applied in many areas such as automobiles,military industry.However,due to the hexavalent chromium existing in the Dacormet coating,the environment has been destroyed.Currently,there are regulations and restrictions on chromium in the world clearly,so chromium-free is a development trend of coating technology.It is imperative to research a new environmentally friendly,chromium-free Dacromet technology.Directed to several key technical issues of coating component design,from the perspective of coating component,coating synthesis and painting process,coating basic properties and corrosion resistance research,this thesis designs and syntheses a new type of chromium-free zinc aluminum-based preservative coating,and has been systematically studied for its coating process and electrochemical corrosion resistance.The results show that the surface coating of metal parts prepared using the coating has a good anti-corrosion resistance,and can replace chromium-free Dacromet coatings.The specific research content is as follows:(1)First,this paper has been studied on the formulation design,hydrolysis process and curing conditions.Chromium-free passivation fluid is the main component of this coating,wherein the hydrolysis process and stability of the silane directly affect the appearance,corrosion resistance and storage stability of the final coating.This study designs a five-factor-level orthogonal test,and systematically investigates the influence of hydrolyzed solvent,p H value,additive,temperature.Finally,determines the optimum chromium-free passivation liquid formulation.(2)Based on the chromate free passivation solution above,this paper optimizes multiple factors including composition of coating,specification and dosage of zinc powder and aluminum powder and coating assistant.Finally determines the formulation of chromium-free zinc aluminum anticorrosive coating.Then the experiment uses immersion centrifugation to coate the metal parts,research and analysis of specific process parameters,which including dip coating time,forward and reverse speed of the centrifuge,centrifugation time,besides the temperature and time of baking and curing.Finally,cool naturally and obtain zinc-aluminum of chromium-free coating.(3)Using SEM,EDS,XRD and other methods to study the microstructure and composition of the coating,then characterize and analyze the basic performance and anticorrosive properties of the coating systematically.The results show that the coating has good covering power,uniform paintability and excellent anti-corrosion performance.It can resist neutral salt spray for more than 900 h;the salt water immersion results show that the coating surface only changes in color after being immersed in salt water for 10 days,and no metal substrate is exposed and corroded,which proves the good anti-corrosion performance of the coating.The results of the electrochemical anti-corrosion performance study show that,compared with the blank sample,the Q235 steel sample coated with a chromium-free zinc-aluminum anti-corrosion coating exhibits excellent corrosion resistance.The self-corrosion potential,self-corrosion current,and corrosion resistance have all been greatly improved,which further proves that the chromium-free zinc-aluminum coating has very excellent anti-corrosion protection performance for the metal substrate. |
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