Effect of surface plastic deformation on hydrogen embrittlement in Al-Zn-Mg alloy

Al-Zn-Mg alloys in T6 temper are susceptible to stress corrosion cracking based on hydrogen-induced intergranular cracking. Over-aging is effective to suppress hydrogen embrittlement, but results in loss of strength. In this study, sliding friction treatment (SFT) and subsequent aging treatment were applied to an Al-4.4mass%Zn-1.4mass%Mg ternary alloy in order to suppress hydrogen embrittlement without decreasing strength. Mechanical properties and hydrogen embrittlement susceptibility were evaluated by tensile tests in two environments: dry nitrogen gas and humid air. Hardness measurement showed that SFT resulted in increment of the hardness near the specimen surface. The specimen processed by SFT and subsequent aging showed the higher strength compared to the T6-tempered one. Moreover, hydrogen embrittlement susceptibility of the specimen processed by SFT and aging was lower than that of T7-tempered one. Fracture surface observation revealed that intergranular cracking was suppressed by SFT and aging. Therefore, SFT followed by aging was effective for the concurrence of high strength and resistance to hydrogen embrittlement.