Fracture Mechanics and Acoustic Emission Response of Retrogression-Reaged 7075-T6 Aluminum Alloy

摘要

Stress corrosion cracking of high strength, structural aluminum alloys, such as 7075 in the T6 temper, is a commonly encountered problem. Recently, an alternative heat treatment, known as retrogression and reaging, has been proposed. It is purported that this heat treatment imparts a stress corrosion cracking resistance for 7075-T6 equal to that of the T73 temper, with only a negligible decrease in yield strength. In order to fully characterize this heat treatment, the plane strain fracture toughness, KIc, and the resistance to fatigue crack growth were compared to those of the same alloy in the normal T6 condition. Small increases in each of these mechanical properties were detected. The acoustic emission (AE) response to crack growth during testing was also investigated. It was determined that the number of AE signals is proportional to the crack length or total crack area. This response is consistent with proposed mechanisms for acoustic emission in this material. It is further noted that no significant difference exists in the AE response of 7075-T6 in the normal and retrogression-reaged conditions. (Author)