The Delayed Fracture of Aluminum Alloys.
Abstract
The fundamental mechanism of stress-corrosion cracking (SCC) has been studied for high-purity Al-Zn-Mg alloys. Earlier work at our laboratory and elsewhere established that hydrogen embrittlement is involved in the SCC mechanism. Moreover, we previously proposed that a Mg-H interaction exists that facilitates hydrogen entry into the alloy and its concentration at the grain boundary, leading to embrittlement. In the present work, we demonstrated the adverse effect of Mg in the bulk metal and in the oxide film on SCC. SCC testing of alloys whose surface oxide-films were removed so bulk composition effects could be studied, revealed that SCC susceptibility increases with increasing Mg to Zn wt% ratio. In film composition experiments, removal of the Mg-rich film that forms during heat treating, and replacing it with a Mg-free film by anodizing in tartaric acid decreased the susceptibility of an Al-Zn-Mg alloy. Moreover, susceptibility decreased with an increasing anodized-film thickness. Fractographic studies revealed that pitting corrosion initiates intergranular SCC in these alloys. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1981
- Accession Number
- ADA095732
Entities
People
- David Venables
- John A. S. Green
- Joseph R. Pickens
Organizations
- Martin Marietta