Effects of alloy compositions on hydrogen embrittlement of Al–Mg–Si based alloys

Abstract

Effects of alloy compositions on hydrogen embrittlement was studied by means of slow strain rate testing, using Al–Mg–Si based alloys containing different amounts of excess Si, Mg2Si and Cu. An Al–1.12 mass%Mg2Si–0.35 mass%Si alloy hardly showed degradation in ductility when tested at the strain rate of 10−7/s in a high humidity atmosphere of 90% R.H, compared to the ductility obtained by testing at the strain rate of 10−4/s. In contrast, the ductility of an Al–1.11%Mg2Si–0.81%Si alloy obtained by testing at 10−7/s was lower than that at 10−4/s in the humid air. By means of SEM/EDS analysis, Si-rich precipitates were observed on intergranular fracture surfaces of the embrittled alloy. These results suggested that hydrogen embrittlement was clearly observed with an increase in excess Si content. The ductility of an Al–1.81%Mg2Si–0.80%Si alloy obtained by testing at 10−7/s, however, was larger than that at 10−4/s in the humid air. The same tendency was observed in commercially available 6070, 6013 and 6066 aluminum alloys. These results meant that the Al–Mg–Si based alloys with excess silicon contents did not always show hydrogen embrittlement. Discussion was made on the above phenomena.