Localized Electrochemical Corrosion Cells.
Abstract
The objective of this research has been to characterize the chemical and electrochemical nature of the localized corrosion cell on aluminum alloys and to relate the environment to the rate of stress cracking of AA7075. It was demonstrated that the environment, as represented by various anions in solution enters into the stress cracking process in a specific way. The reaction at the crack tip is chemical in nature. There are significant changes in pH and Al(3+) concentration within the crack. These changes have been measured and are dependent on the anion in solution as well as the applied potential. The environment within the crack may be altered as well as concentrated, e.g. nitrate ion may be reduced to ammonia during the cracking process. The low pH - of approximately 3 - is explained by the hydrolysis of the aluminum ion, but it is not the hydrolysis, per se, that is responsible for the accelerated corrosion, because the corrosion rate of aluminum in different salts at the same pH is significantly different. All of the studies taken together convincingly demonstrate that chemical reactions at the crack tip determine the rate of crack growth in AA7075.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1982
- Accession Number
- ADA111591
Entities
People
- R. T. Foley
Organizations
- American University