Coating for aluminum alloy aerostructures

A method for manufacturing an airfoil element (20;

• 100), the airfoil element comprising:
• an airfoil (102) having a pressure side and a suction side;
• an aluminum alloy substrate (22);
• and
• a coating system (23) atop the substrate and comprising in at least one location:
• an anodize layer (24) having a thickness (TA) of 1.0 micrometer to 5.0 micrometers;
• a sealant (36) filling at least 5.0% of porosity in the anodize layer or at least 0.7% of an apparent volume within a height of the anodize layer;
• a sealant primer (40) filling 50.0% of porosity in the anodize layer or at least 6.5% of an apparent volume within a height of the anodize layer and extending at least flush to the anodize layer;
• a second primer (44) over the sealant primer and having a thickness (TS) of 5.0 micrometers to 50 micrometers;
• and
• a polymeric coating (48) having a thickness (TT) of 10.0 micrometers to 1.0 millimeter, the method comprising:
• applying the anodize layer by boric sulfuric acid anodization;
• and
• applying the sealant by immersing the anodized substrate in an acid solution with corrosion inhibitor;
• applying the sealant primer by spraying;
• applying the second primer by spraying;
• and
• applying the topcoat by spraying, wherein:
• the sealant primer is sprayed from less viscous stock than the second primer;
• and/or
• the sealant primer stock has a methyl ethyl ketone (MEK) solvent and a phenolic resin and epoxy resin base with strontium chromate;
• and/or
• the second primer stock is a chrome-free, water-borne, chemically cured, polyamide primer.