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

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 beta 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.