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

Abstract

In Part I (BCJ, 1976, 11, 143) using aluminium specimens electrolytically notched (e.n.) by anodic dissolution, it was demonstrated that these specimens reached failure in s.c.c. in a shorter time than did mechanically notched (m.n.) specimens, tested under the same conditions. Similar results were obtained on e.n. and m.n. specimens after mechanical ‘denotching’. These results, combined with the fact that, for Al alloys, the rate determining stepfor s.c.c. is the solid state diffusion of mobile Al⁺³, were taken to provide evidence that during the e.n. preparation of Al alloy specimens, and during the spontaneous first step of S.c.c., sensitisation is brought about by diffusion of Al⁺³ causing structural disorder on immobile Al⁺³ and hence loss of cohesion. The results also provide indirect evidence that sensitisation is due to active path formation.

Exactly similar experiments, now carried out on m.n. and e.n. and ‘denotched’ steel specimens (in which the rate determining step is diffusion of corrosive ions into the metal), revealed no difference in time to failure between the m.n. and e.n. specimens. These results provide indirect confirmation of the interpretation given to the observed sensitisation produced in Al alloys.