Stress Corrosion Crack Propagation and Cathodic Protection in Medium Strength Aluminum-Zinc-Magnesium Alloys

Abstract

Two aluminum alloys were used in this investigation, one containing 4 wt % Zn and 2 wt % Mg, the other 4.3 wt % Zn and 2.4 wt % Mg. Both alloys were made from very pure metals. A static stress corrosion test was carried out on the more dilute alloy, and extension steps of a few millionths of an inch were recorded. A cathodic current was found to decrease the rate of crack propagation, but not stop it completely. The results were explained on the basis of changes in pH of the 3% NaCl electrolyte inside the crack. Dynamic stress corrosion tests were also carried out.