Microstructure and Corrosion Resistance of Molybdenum and Aluminum Coatings Thermally Sprayed on 7075-T6 Aluminum Alloy

摘要

Pitting corrosion upon 7075-T6 high strength aluminum alloy, often associated with cathodic intermetallic particles decreases its fatigue life by a factor of about 6 to 8. In order to improve the corrosion resistance of this alloy, arc spray coatings of molybdenum and aluminum are applied. The open circuit potential and potentiodynamic polarization measurements made in 3.5% NaCl naturally aerated solution reveal that the molybdenum coating, which has an excellent hardness, shifts the 7075-T6 corrosion potent ial (E_(corr)) to noble values and increases slightly the corrosion current density (i_(COrr)). On the contrary, when the aluminum coating alloy is applied, both E_(con) and i_(corr) are shifted to better values. The increaseof i_(corr) of the alloy when molybdenum coating is applied can be attributed to the high porosity present into the coating. On the other hand, microstructure observations of the aluminum coating reveal a small porosity, which helps the formation of passive oxide film that protects the coating against a further corrosion.