Oxide Film Formation on a Microcrystalline Al Alloy in Sulfuric Acid

S. C. Thomas
1997 Journal of the Electrochemical Society  
The differences in the electrochemical behavior of a rapidly solidified, two-phase (matrix and dispersoid) Al-based alloy containing Fe, V, and Si (FVSO812 alloy) and the bulk form of its matrix and dispersoid phases were investigated in sulfuric acid. FVSO812 exhibited generally higher electrochemical activity than the matrix material due to the presence of the very active dispersoid phase in the alloy. Impedance studies indicated that the properties of thin films formed on the FVSO812 and
more » ... ix substrates during only 5 mm of anodization are similar, whereas the film formed on the alloy during 2.5 h of anodization was substantially less resistive and contained a thinner and/or damaged underlying barrier oxide compared to a comparable film formed on the matrix. Compared to the classical structure of porous Al oxide films with underlying barrier oxide, the oxide film on FV50812, as seen by TEM, was thinner; with an intermittent barrier oxide underlying a porous oxide of contorted morphology. Evidence is seen for the loss of dispersoids from the oxide film, leaving voids throughout its structure, perhaps the reason for its lack of physical adherence and its limiting thickness.
doi:10.1149/1.1837596 fatcat:c3qfkp3f2ra2rjb32lzwl4r2bm