Beta phase distribution in Al-Mg alloys of varying composition and temper

• Published in: Corrosion science 2020-06, Vol.169, p.108618, Article 108618
• Main Authors: McMahon, Matthew E., Haines, Raewyn L., Steiner, Patrick J., Schulte, Justine M., Fakler, Sarah E., Burns, James T.
• Format: Article
• Language: English
• Subjects: Al-Mg alloys; Aluminum base alloys; Ammonium peroxodisulfate; Ammonium persulfate; Beta phase; Electron backscatter diffraction; Grain boundaries; Intergranular corrosion; Intergranular stress corrosion cracking; Nitric acid; Nitric acid mass loss test; Phase distribution; Sensitization; Stress corrosion cracking; Susceptibility
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2020.108618

•New sensitization quantification method without mass loss assumption (ie. G67).•Analysis on samples taken from fracture specimens tested for IG-SCC susceptibility.•More accurate correlation between linear grain boundary β phase coverage and IG-SCC.•Correlation between β coverage and IG-SCC affected by yield strength.•Results provide insight into improving ASTM G67 test method. The ASTM G67 Nitric Acid Mass Loss Test (NAMLT) is not a universally accurate proxy for intergranular stress corrosion cracking (IG-SCC) susceptibility in Al-Mg alloys. This study aims to understand this discrepancy via an electron backscatter diffraction (EBSD) and ammonium persulfate etching/overlay analysis to characterize the linear grain boundary β coverage (LGBBC). Testing at three NAMLT levels of AA5083-H131, AA5083-H116, AA5083-SHTQ, and AA5456-H116 derived from fracture specimens demonstrates that LGBBC is a more accurate metric to describe the IG-SCC susceptibility, however the correlation degrades for materials with divergent yield strengths. These results provide insights necessary to improve upon ASTM G67.