Stress corrosion cracking of superplastically formed 7475 aluminum alloy
Journal
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Journal Volume
28
Journal Issue
10
Pages
2113-2121
Date Issued
1997
Author(s)
Abstract
The effects of biaxial superplastic deformation and postforming heat treatment upon the stress corrosion cracking (SCC) of a fine-grained 7475A1 alloy plate have been investigated. For all postforming tempered conditions, increasing the extent of superplastic deformation, which created more cavitations, would decrease the mechanical properties, the SCC resistance, and the corrosion resistance. The influence of cavitation on the decay of elongation of the superplastically formed workpieces is larger than that on the decay of its strength. Post-forming tempered by retrogression and reaging (RRA) treatment could effectively improve the SCC resistance of workpieces in postforming T6 temper while not sacrificing the strength. However, the benefit of improving the SCC resistance by means of the postforming RRA temper was decreased with increasing the extent of superplastic deformation, because the SCC susceptibility increased as the extent of superplastic deformation increased for each postforming tempered-condition. The cavitation led to more anodic corrosion potential and pitting potential and to an increase in both corrosion current density and passive current density, which would increase the SCC susceptibility.
Type
journal article