The Study Of Preparation And Corrosion Resistance Of Rare Earth Modified ZnAl-LDHs Films

Aluminum alloys is one of the most used nonferrous metals in the industrial field,due to its characteristics of small density,high strength,excellent processing and forming and corrosion resistance.Since the beginning of the 21st century,when the development of Marine resources in China draws vast attention,aluminum alloy materials have been broadly applied in this field.However,the oxidation film of aluminum alloy would be corroded in the solution containing chloride ions,as a result,affect the workpieces' time and performance,especially in the Marine field.At present,chromate passivation film has widely used in corrosion protection of aluminum alloy due to its advantages of high corrosion resistance and low cost.However,Cr???and its derivatives are with high toxicity and carcinogenicity,and the liquid waste processing is comparatively difficult.Thus,finding a new type of surface treatment technology substituting chromate passivation film to improve the corrosion resistance of aluminum alloy is necessary.In the last decade,the Layer double hydroxides?LDHs?film has been applied as corrosion protection on aluminum alloys due to its excellent corrosion resistance and environmental friendlinessTo further improve the corrosion protection performance of aluminum alloy,the rare earth modified ZnAl-LDHs films were prepared on the surface of 6061 aluminum alloy by in situ growth method,electrodeposition method and the code position.Then we exploited XRD,XPS,SEM,EDS,EQCM,electrochemical workstation technology,etc.,to study the influence on growth behavior,structure and corrosion resistance of rare-earth modified ZnAl LDHs.And we used the same approach to study the influence of the hydrothermal pretreatment of aluminum alloy to prepared ZnAl-LDHs films by in-situ growth method on growth behavior,structure and corrosion resistance,and discussed the mechanism of the effects.?1?When ZnAl-LDHs were prepared by in situ growth method,the La could promote the crystallization nucleation rate of LDHs and inhibit their growth rate,thus refine LDHs nanosheets and making it more difficult for Cl^-to approach the aluminum alloy substrate through the LDHs film.Meanwhile,in the corrosion process,La3+would form a self-repairing La?OH?₃ film at the corrosion crack to provide second protection.?2?When ZnAl-LDHs was prepared by electrodeposition,rare-earth element Ce increased the growth rate of LDHs.The presence of Ce will enhance the cathode polarization and promote the cathodic reaction in the electrodeposition process,and enhance the thickness of LDHs film.?3?When preparing ZnAl-LDHs by co-deposition method,the rare-earth element La could also promote the crystallization nucleation rate of LDHs and inhibit its growth rate,thus retinene LDHs nanosheets and make the tiny of ZnLaAl-LDHs nanosheets more evenly distributed and of higher density in sol-gel solution,and more Cl^-was captured by LDHs during the process of Cl^-through the sol-gel coating.However,excessive content of La will excessively inhibits the growth of LDHs nanosheets,resulting in the decrease of LDHs content.?4?Al?OH?₃ and AlO?OH?formed on the surface of aluminum alloy after water heat treatment,which can be used as the precursor of LDHs formation process.This can improve the crystallization nucleation rate of LDHs and inhibit the growth space of it,thus refine LDHs nanometer sheet.