CORROSION FATIGUE AND STRESS CORROSION CRACKING OF AN ALUMINUM-5% MAGNESIUM-4% ZINC ALLOY TOTALLY IMMERSED IN 3% NACL AND OTHER CORRODENTS
Abstract
Corrosion fatigue and stress corrosion tests were made on aluminum-5% Mg-4% Zn alloy in two conditions of heat-treatment, aged to peak hardness at 120 C and at 150 C. All crack paths were intercrystalline under both corrosion fatigue and stress corrosion conditions, although air fatigue cracks in this material are mainly transcrystalline. The slopes of the S/log n curves for 20 and 180 c/min were similar, but the 1500 c/min curve had a smaller slope. This difference was clearly associated with the knee in the 20 c/min curve that was not evident at the higher test frequency. The effects of both anodic and cathodic polarization were studied. Marked changes in crack growth rate were observed when a fatigue specimen was alternately made anodic and cathodic in a 3% NaCl solution against either a Pt or Al electrode with an externally impressed current. Similar changes in crack growth rate could be obtained with impressed currents under steady stress corrosion conditions. Stress corrosion crack growth rates were shown to be dependent on the chloride ion concentration of electrolytes used, suggesting a metal dissolution mechanism of stress corrosion in this material.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1965
- Accession Number
- AD0478909
Entities
People
- E. G. Sampson
- P. J. Forsyth
Organizations
- Royal Aircraft Establishment