Stress Corrosion Testing of 5083 Aluminum^*

The stress corrosion susceptibility of thermomechanically processed 5083 aluminummagnesium alloy was determined in a 3.5 Wt% sodium chloride environment. Alternate immersion C-ring and constant elongation rate tensile tests were performed. Comparison of the test results indicated that both techniques revealed the susceptibility of short transverse specimens to stress corrosion cracking. Potentiokinetic determinations of the characteristic pitting potential (Ep) and protection potential (Epp), were made. In deaerated 3.5 Wt% sodium chloride, Ep is −740 mV and Epp is −770 mV versus a standard calomel reference electrode. Standard tensile tests (air environment) were also conducted to generate base line strength data. The short transverse tensile specimens had a nominal 260 MPa (38 ksi) yield strength and 6.5% total elongation. Comparison of base line data with the stress corrosion data revealed that constant elongation rate test results are dependent upon a balance of normal ductile failure and the corrosion induced failure modes. Impressed potentials equal to or more noble than the pitting potential (Ep) generated the maximum degradation of mechanical properties while impressed potentials more negative than the protection potential (Epp) did not alter the mechanical properties of 5083 aluminum. Thus, the development of constant elongation rate tensile tests required an in-depth understanding of the corrosion mechanisms and the mechanical properties of 5083 aluminum. Alternate immersion C-ring tests generated specimen pass or fail information which indicated susceptibility of staticly loaded (80% of yield) specimens to stress corrosion induced failure. Test results showed that only four of eight specimens tested contained stress corrosion failures. Thus, cracking failures were random in nature and test results yield only arbitrary measures of stress corrosion susceptibility (pass or fail).