Environment-Induced Crack Initiation in Aluminum Alloys – Experimental studies since the 1950’s and future opportunities

The initiation of environment-induced cracking (EIC) in aluminum alloys typically dominates the total life during both service-life for structural applications and for smooth tensile test specimens subjected to conventional standard EIC testing. Experience and literature published over the past 70 years have been reviewed, and in some cases re-interpreted. The authors propose we are now well-positioned to use today’s advanced experimental techniques to properly elucidate the EIC initiation phenomena for aluminum alloys. EIC initiation typically involves at least three stages: incubation, intergranular cracking that may ‘arrest’ and a transition to propagating cracks where the mechanical driving force exceeds a threshold, KIEIC, and a surface feature has become a crack potentially propagating at mm/yr. Alloy developers, product designers and commercial users now need quantitative EIC initiation and growth data from accelerated laboratory testing that is directly relatable to actual surface conditions and the expected service conditions.