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Accession Number:
ADA095732
Title:
The Delayed Fracture of Aluminum Alloys.
Descriptive Note:
Rept. for 1 Jan-31 Dec 80,
Corporate Author:
MARTIN MARIETTA LABS BALTIMORE MD
Report Date:
1981-01-01
Pagination or Media Count:
60.0
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
Distribution Statement:
APPROVED FOR PUBLIC RELEASE
