To mitigate stress corrosion cracking (SCC) susceptibility in Al-Zn-Mg alloys, specimens simulating welded structures were fabricated from thick plates treated with friction stir processing (FSP), and their SCC susceptibility was evaluated through alternating saltwater immersion testing and microstructural analysis. Although age hardening recovers the strength of the weld heat-affected zone to levels comparable to the base material, SCC susceptibility remains an issue. FSP was applied to refine the grain structure and randomize the crystallographic orientations of surfaces exposed to corrosive environments, aiming to reduce SCC while retaining mechanical strength. Since SCC initiation was difficult in welded specimens, four-point bending tests were conducted as a comparative test, and intergranular corrosion depth and extent were used as representative indicators of SCC susceptibility. While no macroscopic cracks appeared in the welded specimens after immersion testing, cross-sectional observations revealed that FSP-treated surfaces showed pitting and grain boundary detachment, whereas untreated base material exhibited sharper intergranular corrosion with crack-like features. These results demonstrate that microstructural control through FSP is an effective strategy for suppressing SCC initiation in practical welded aluminum alloy structures.
BABA et al. (Wed,) studied this question.