Identification of the Factors Governing the Origin and Propagation of Corrosion Failure of Organically Coated Aluminum Aerospace Alloys
Abstract
The effect of pretreatment and alloy microstructure on the rate of scribe-creep caused by under-paint corrosion on AA2024 was examined. Scribe-creep experiments were conducted on epoxy polyamide coated AA2024-T3 in 80% relative humidity at 25C, 40C, and 50C with an intentional scratch through the organic coating into the substrate. Scribe-creep was enhanced by test temperature regardless of surface pretreatment with activation energy of 30- 40 kJ/mol, as well as by artificial aging of the alloy and certain alloy surface pretreatments before the coating was applied. Scribe creep rates were accelerated at all temperatures by pretreatments that increased the surface copper coverage or left a high capacity for Cu-replating such as in the form of Cu-containing intermetallic compounds. Scribe creep was mitigated by pretreatments such as NaOH + HNO3 as well as by chromate, molybdate and cerium acetate inhibitors that minimized Cu replating. Instrumented arrays were used to develop a galvanic corrosion model of scribe creep propagation that could account for many of the material, pretreatment and inhibitor effects seen on scribe creep propagation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 14, 2005
- Accession Number
- ADA437941
Entities
People
- Daryl A. Little
- John R. Scully
Organizations
- University of Virginia