The Preparation And Properties Of Rare Earth Elements Modified Anodic Films On Aluminum

In this paper,three methods(pre-treatment by precursor method, anodic oxidation solution containing rare earth(RE) salt and rare earth sealing) to the preparation of rare earth modified anodized aluminum alloy.Potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) were used to study the corrosion behavior of rare earth modified anodic oxide film.The anodic film surface was observed by scanning electron microscopy(SEM),the composition of the oxide film was analized by energy dispersive X-ray analysis(EDXA) and X-ray diffraction(XRD).By the precursor method in MgCl₂ solution containing rare earth salts,rare earth was introduced into AlMg-LDHs hydrotalcite on the high purity aluminum surface,which was then anodized,Al-Mg-RE complex anodic oxide films were got.The influences of rare earth concentration, processing time,processing temperature and pH value on rare earth content in hydrotalcite were studied.Highest content of RE was found in the AlMg-LDHs hydrotalcite on the aluminum surface,which was treated in 1 mol/L MgCl₂ solution(80℃and pH=9) with 50g/L Ce(NO₃)₃ and 50g/Lçš„Nd(NO₃)₃ for 1 hour.Using the same method,highest content of RE was found in the AlNi-LDHs hydrotalcite on the high purity aluminum surface,which was treated in 1mol/L Ni(NO₃)₂ solution(90℃and pH=8) containing 75g/L Ce(NO₃)₃ and 85g/L Nd(NO₃)₃,for 1 hour. RE complex anodic oxide films display better performance in chemical properties and mechanical properties.It was found that the rare earth modified oxide film were more compact with much smaller pores and increased hardness,hole diameter reduced from 80～90 nm to 40 nm.The film thickness analysis result showed that average growth rate of modified anodic films raised up to 110%.XPS analysis showed that Ce is present in the film as CeO₂ and Ce₂O₃,and Nd is present as Nd₂O₃. Modified oxide films were still typically amorphous the same as that of usual anodic aluminum.In neutral,acidic and basic NaCl solutions,the rare earth modified films showed obviously improved corrosion resistance.The effect of element Ce on increasing corrosion resistance of the film is better than that of Nd.The rare earth salt modified anodic films showed higher R_p value and lower C_p than those of the anodic film on pure aluminum in neutral NaCl solution.The semiconductor function of rare earth modified anodic films is changed from n-type to p-type.The properties of anodic films on purity aluminum formed in sulfuric acid electrolyte containing rare earth salt were studied.The role of rare earth element in the process of anodizing was analyzed by component test,microstructure observation and electrochemical test.The results showed that rare earth elements can accelerate the growth rate of aluminum oxide film about 5%,and also decreased porosity and increased hardness.Compared with anodic films modified by single rare earth salt,electrochemical test showed that the anodic film modified by compound rare earth salts has better corrosion resistance.The element Ce showed better effect on increasing corrosion resistance of the film than Nd.This research studied the no-toxic materials in sealing methods for anodic films on ZL201 aluminum alloy,and Ce and Nd were introduced in aluminum anodic film.Using compound sealing with Ce salt and Nd salt,the corrosion resistance of the anodic film was great improved.The sealed anodic film has been developed to improve the corrosion resistance of anodic films without the use of chromates and nickelates.