| New oxide coatings (UC-1 and UC-2) that are protective, adhesive and chromate-free have been developed for a particular Mg alloy (WE43) surface using a dc/ac current-voltage program. The UC-1 and UC-2 coatings differ in the anodization bath composition and the pre- and post-treatments employed. All coatings are porous, with higher anodizing currents and longer times yielding thicker films. However, the use of a constant anodizing current, followed by a period of time for current decay, produces pores sealed deeper into the coating. A barrier film exists in the UC-1, but not in the UC-2 coating. The coating corrosion behavior was characterized in 0.86 M NaCl using ac impedance, cyclic voltammetry (CV) and open circuit potential (OCP) measurements. The UC-1 coating exhibited a much higher resistance than did the UC-2 coating, and performs similarly to a standard anodized Al alloy in both the aqueous NaCl and jet fuel media. |
