Effect of Sensitization on Hydrogen Embrittlement in a 5083 Aluminum Alloy

The 5000 series non-heat-treatable Al -Mg alloys are widely used as structural members, because of excellent combination of weldability, corrosion resistance and mechanical properties. It is well known that these alloys can become susceptible to inter-granular stress corrosion cracking. In the previous paper, the authors revealed that hydrogen embrittlement (HE) takes place in weld corner (fusion zone adjacent to HAZ) in an MIG-welded joint of 5083 alloy. In this study, the base material and MIG-welded joint of the 5083 alloy were sensitized, and their resistance to HE was investigated by two methods: humid gas stress corrosion cracking (HG-SCC) and slow strain rate tensile (SSRT) tests. The results obtained were discussed, in comparison with the previous results obtained in the non-sensitized joint. Discussion was also made in terms of the difference of the two testing methods. Extension of HG-SCC cracks were observed for all sensitized 5083 alloy samples, base and welded samples tested in humid air, and hence HE was confirmed. Fractography and surface observation on the crack tip of HG-SCC revealed that the crack propagates in a transgranular manner. The extent of HG-SCC was greater in the present sensitized specimens in all the locations except the weld corner, but the position dependency has been the same: crack propagation amount was largest in the weld corner. On the other hand, SSRT test results did not indicate any reduction in ductility or strength when testing environment was changed from dry nitrogen gas to humid air. Therefore, it is concluded that HG-SCC test is more sensitive for detecting HE of 5083 alloy