Humid gas stress corrosion cracking in MIG-welded 5083 aluminum alloy plate

Alireza Ghorani*, Goroh Itoh**, Tomoyuki Ohbuchi*** and Tomoya Kiuchi***
*Major in Complex System Science, Graduate School of Science and Engineering, Ibaraki University
**Department of Mechanical System Engineering, Faculty of Engineering, Ibaraki University
*** Major in Mechanical System Engineering, Graduate School of Science and Engineering, Ibaraki University

In 5000 series (Al-Mg) alloys, hydrogen embrittlement (HE) becomes a concern when Mg content exceeds 5%. The local Mg content will become higher than 5% due to solidification segregation in the weld joint of 5083 alloy. In this study, as illustrated in Fig. 1, resistance to HE of MIG -welded 5083 aluminum alloy at three areas (weld center, weld corner and HAZ) has been investigated by newly developed humid gas stress corrosion cracking (HG-SCC) test. Slow strain rate tensile (SSRT) test on base metal and welded joint has been also conducted for comparison.

The HG-SCC test results are summarized in Table 1. It has been newly revealed that HG-SCC crack extends only in the sample of weld corner, confirming HE in this area. For the other areas, HG-SCC crack does not propagate, confirming HE resistance of these areas. From the results of SSRT test in humid air, neither the base nor welding material showed reduction in strength or ductility compared to those obtained from the tests in dry nitrogen gas, as shown in Fig. 2. Therefore, it has been concluded that HE in 5083 MIG welds is only detectable by HG-SCC test. The reason for this should be in the fact that HG-SCC test can specifically test different local areas, while the softest area (weld center) always deforms preferentially and fractures in SSRT test.

[Published in Materials Transactions, Vol. 61, No. 2 (2020), pp. 330-338]

Fig. 1 Configuration and morphology of compact tension (CT) test piece, cut from base metal (a) and welded materials (b) to (d). (I) overall view of test pieces, gray line represents weld line, (II) location of the notch with respect to the weld centerline, (III) details of the CT test piece. D: distance of the notch from the weld centerline. The values of D are 0 for (b), 7mm for (c) and 12mm for (d).

Table 1 Summary of the HG-SCC test results. N: Number of the samples tested, Δa: crack propagation length, Δam: average of Δa.

Fig. 2 Stress-strain curves of the specimens SSRT-tested.