PRECIPITATE-FREE ZONES AND STRESS-CORROSION CRACKING IN A TERNARY Al-Zn-Mg ALLOY.
Abstract
A study was made of the role of the precipitate-free zone (PFZ) in the stress-corrosion cracking of a ternary Al-5.3 w/o Zn-2.5 w/o Mg alloy in aqueous chloride solutions. For alloys heat treated to give the same hardness (140 D.P.N.), susceptibility was found to depend on the width of the PFZ (in the range 0.04-0.35 microns), both the time to initiate and to propagate stress-corrosion cracks decreasing significantly with decreasing PFZ width. Application of small anodic currents (e.g. 0.2 mA/sq cm) reduced failure times by about two orders of magnitude, while cathodic currents inhibited failure. Fractographic studies indicated that the mode of stress-corrosion failure differs from that obtained in normal tensile fracture; no evidence for discontinuous crack propagation was found. These and other observations are discussed in terms of the proposed mechanisms of stress-corrosion cracking, and shown to be consistent with a mechanism involving localized anodic dissolution of plastically deforming solid solution within the PFZ. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1969
- Accession Number
- AD0681052
Entities
People
- A. J. Sedriks
- E. N. Pugh
- P. W. Slattery
Organizations
- Martin Marietta