Mitigation of Intergranular Stress Corrosion Cracking in Al-Mg by Electrochemical Potential Control

Intergranular stress corrosion cracking in the Al-Mg alloy AA5456-H116 is suppressed via cathodic polarization in 0.6 M NaCl, saturated (5.45 M) NaCl, 2 M MgCl2, and saturated (5 M) MgCl2. Three zones of intergranular stress corrosion cracking (IG-SCC) susceptibility correlate with pitting potentials of unsensitized AA5456-H116 and pure beta phase (Al3Mg2) in each solution. These critical potentials reasonably describe the influence of alpha Al matrix and beta phase dissolution rates on IG-SCC severity. Complete inhibition occurred at applied potentials of -1.0 V and -1.1 V versus saturated calomel electrode (V (SCE)) in 0.6 M NaCl. Whereas only partial mitigation of IG-SCC was achieved at -0.9 V (SCE) in 0.6 M NaCl and at -0.9, -1.0, and -1.1 V (SCE) in the more aggressive environments. Correlation of pitting potentials in bulk environments with IG-SCC behavior suggests an effect of bulk environment [Cl-] and pH on the stabilized crack tip chemistry.