Literature Data and Corrosion Testing of Hard Anodized and Duplex Sealed 7075-T7351 and 7050-T7451 Wrought Aluminum Alloy Plates after Cyclic Loading

Heat treated 7000-series aluminum alloys exhibit the highest strength and toughness amongst wrought aluminum alloys, and are used for a variety of applications in the defense and the aerospace industry. The corrosion resistance of these alloys is strongly dependent on final thermo-mechanical and tempering treatment. Many surface modification techniques are used to protect these alloys against general, exfoliation and pitting corrosion. Hard anodizing is a surface modification technique that imparts corrosion and wear resistance to 7000-series aluminum alloy parts. However, if the anodized parts experience cyclic loading conditions, there is a risk that the brittle anodized layer may undergo cracking thereby compromising the corrosion resistance of the 7000-series aluminum components in service. This paper details the results of an investigation undertaken to evaluate the corrosion behavior 7075-T7351 and 7050-T7451 aluminum samples that were anodized and duplex sealed prior to cyclic loading. The aluminum samples were hard coat anodized per MIL-A-8625F and cycled between 0-31 ksi (0-214 MPa) for 4000 cycles prior to the accelerated corrosion tests. A hypothesis to explain the corrosion behavior is presented.