Contribution to the Interpretation of the Formation of the Active Path in Stress Corrosion Cracking of Aluminium Alloys: I. Indirect evidence from electrolytically notched specimens

With the object of interpreting the formation of the active path in stress corrosion cracking (s.c.c.) of metals and alloys, a new, electrolytic, method of preparing notched specimens was employed. Double notched specimens of Al–2 · 5 wt- % Mg alloy were so prepared, using several different current densities to prepare the notches. Their behaviour was then compared with that of mechanically notched specimens under accelerated laboratory stress corrosion conditions in M NaCl with differing impressed current densities. In some instances the notches were removed mechanically before testing (‘denotched’ specimens).

For each category of specimen, applied stress vs specimen life (time to cracking) was established. Results obtained from this procedure indicated that, for this alloy, a sensitisation takes place during the first step of stress corrosion cracking, i.e., localised anodic dissolution (pitting) of the stressed zone. In the second part of this work, based on further measurements (to be published) it will be shown that this sensitisation corresponds to active path formation, attributable to de-cohesion as a result of fast solid diffusion of mobile (reversibly disordered) Al³⁺.