Corrosion behaviors in physiological solution of cerium conversion coatings on AZ31 magnesium alloy

In this paper, a non-toxic Ce-based conversion coating was obtained on the surface of bio-medical AZ31 magnesium alloys. The micro-morphology of the coating prepared with optimal technical parameters and immersed in physiological solution (Hank's solution) in different time was observed by scanning electron microscopy (SEM), composition of the cerium conversion coating and corrosion products in Hank's solution were characterized by X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS), respectively. In addition, the corrosion property in Hank's solution was studied by electrochemical experiment and immersion test. The results show that the dense Ce-based conversion coating is obtained on the surface of AZ31 magnesium alloys in optimal technical parameters and the conversion coating consists of a mass of trivalent and tetravalent cerium oxides. The cerium conversion coating can provide obvious protection of magnesium alloys and can effectively reduce the degradation speed in Hank's solution. Also the degradation products have little influence on human body.     

A corrosion resistant cerium oxide based coating on aluminum alloy 2024 prepared by brush plating

Cerium oxide based coatings were prepared on AA2024 Al alloy by brush plating. The characteristic of this technology is that hydrogen peroxide, which usually causes the plating solution to be unstable, is not necessary in the plating electrolyte. The coating showed laminated structures and good adhesive strength with the substrate. X-ray diffraction and X-ray photoelectron spectroscopy analysis showed that the coatings were composed of Ce(III) and Ce(IV) oxides. The brush plated coatings on Al alloys improved corrosion resistance. The influence of plating parameters on structure and corrosion resistance of the cerium oxide based coating was studied.     

Corrosion resistance of cerium-based conversion coatings on alumina borate whisker reinforced AA6061 composite

Cerium-based conversion coatings on Al₁₈B₄O₃₃w/6061Al composite surface were obtained by immersing the composite into a solution containing various concentrations of CeCl₃. Results indicate that the susceptibility to pitting for the conversion-coated composites was much lower than that of the untreated composite, and the corrosion resistance of the coated composites was improved markedly; moreover, the concentration of CeCl₃ in the cerium solution affects significantly the corrosion behaviors of the coated composites. The coating obtained from a solution containing 7.5 g CeCl₃ into 1000 ml produced better corrosion resistance on the composite due to the surface being almost covered by conversion coating. EDX and XPS experimental results indicated that the coatings were made up of oxygen, cerium, and aluminum.     

The effect of chromic sulfate concentration and immersion time on the structures and anticorrosive performance of the Cr(III) conversion coatings on aluminum alloys

The main purpose of this study is to develop trivalent chromium, Cr(III), conversion coatings on aluminum alloys. The influence of Cr(III) concentration and immersion time on structures and anticorrosive performance of the coatings has been investigated. Corrosion behaviors of the coatings were evaluated in a 0.5 M H₂SO₄ aqueous solution at room temperature using potentiodynamic polarization. The structure and valence state of the coatings were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The addition of Cr(III) ions to the conversion bath considerably changes structures and compositions of the coatings. The coatings with Cr oxides possess a denser and thinner structure. Moreover, the corrosion resistance of Cr(III) coatings tends to decline with increasing immersion time due to the dissolution of coatings in the dipping period. According to XPS analysis, the Cr(III) conversion coatings are composed of Cr₂O₃, Cr(OH)₃, Al₂O₃, Al(OH)₃, ZrO₂, Zr(OH)₄, AlF₃, and ZrF₄, but no hexavalent chromium component in the coatings. The result indicates that the coatings prepared in the solution with 0.01 M Cr(III) for 5 min have the smoothest and densest structure and the best anticorrosive performance among all of conversion coatings in this work.