Comparison of Test Methods Used to Analyze Stress Corrosion Cracking of Differently Tempered 7xxx Alloys

Abstract

This paper compares and critically analyzes various test methods used to assess stress corrosion cracking susceptibility of the alloy EN AW-7075 (Al-Zn-Mg-Cu) in various temper conditions. Constant load test in an alternating immersion environment was used as the standard reference test. Constant displacement tests in the form of U-bend specimens and four-point loaded bend specimens was conducted in a neutral and acidic salt-spray fog test environment, an alternating salt-spray fog environment and alternating immersion environment. A novel incremental step load test was also carried out, in a continuous immersion environment. It was observed that the susceptibility ranking from U-bend test and the standard constant load test correlated well, while the ranking obtained by the 4-point loaded bend test, showed lower correlation. The same susceptibility ranking was observed in all the test environments. It was shown that the neutral salt-spray fog test environments could potentially substitute the alternating immersion test for testing SCC susceptibility. The T4 treated material showed maximum SCC susceptibility followed by T6 treated and the overaged T7 showed least susceptibility.