Investigation of Aluminum Alloy Protective Coatings
Student: Alen Korjenic
Aluminum alloy 7075-T651 is commonly employed in aircraft airframes for commercial and military application but is susceptible to localized corrosion in the form of pitting and intergranular attack. Corrosion induced damage must be prevented with an actively protective coating system. For this reason, a Mg-rich primer (MgRP) coating was developed for the protection of similar aluminum alloy AA2024-T351. MgRP protects the AA2024-T351 substrate primarily via a sacrificial anode-based cathodic protection where AA2024-T351 is protected from corrosion via Mg oxidation.
Additional protection mechanisms may operate as well and are under investigation, as observations made in the field indicate that Mg(II) corrosion products can chemically deposit onto remote scribe exposing the substrate. Aluminum-based Al-rich primer (AlRP) and composite Magnesium/Aluminum based MgAl-rich primer is also being studied to assess the chemical protection effects (both in solution and as corrosion product) and to investigate its own merit as a reliable coating for corrosion protection of AA7075-T651.
The effect of Mg-based dissolution on solution chemistry is determined via chemical stability diagrams and the microconstituent phases of the alloy are isolated and tested in each Mg2+-affected solution chemistry to evaluate corrosion kinetics. Insights are provided on how coating design impacts corrosion protection performance. Newly considered corrosion protection mechanisms available for MRP sacrificial anode based cathodic protection on aluminum alloys via Mg2+ storage, release, and redeposition are considered.