OXIDE FILM FORMATION ON A MICROCRYSTALLINE AL-ALLOY AT VARIOUS TEMPERATURES IN NEUTRAL BORATE SOLUTION

FVS0812 is a rapidly solidified Al alloy consisting of an intermetalli c (dispersoid) phase, containing Al, Fe, V, and Si, surrounded by a pr edominately Al matrix. The electrochemical behavior and the oxide film structure of FVS0812 were compared to that of its two phases, as well as pure Al, in neutral berate solution at a range of temperatures. Wh ile in acidic solution, FVS0812 is unable to form an adherent, thick, porous oxide film, in 60 degrees C neutral solution, stable, although substantially thinner, porous oxides are formed on Al, FVS0812, and th e matrix. In contrast to its dissolution in acidic medium, the dispers oid phase is retained within the porous film formed on the alloy in ne utral solution. However, the dispersoid phase also causes the formatio n of a somewhat contorted porous oxide structure. Impedance measuremen ts suggest that solution penetration into fine flaws in the barrier ox ide at the barrier/porous oxide interface, a phenomenon exacerbated by increased temperature and time at applied potentials, is more prevale nt for FVS0812 than for Al and the matrix.