On the stress corrosion cracking of Al−Li alloys: The role of grain boundary precipitates

Abstract

The stress corrosion cracking (SCC) behavior of precipitation-hardened alloys may depend on a large number of microstructural parameters that vary during fabrication and heat treatment, such as grain size, grain boundary (GB) solute segregation, matrix precipitate size, GB precipitate size, precipitate-free zone size, and matrix slip character.[1] Since all of these factors vary simultaneously during normal heat treatments, it is difficult to assess independently the contribution of each microstructural factor to the SCC behavior of an alloy. In particular, a series of experiments was designed which would allow the evaluation of the role of GB precipitates in the SCC behavior of Al−Li and Al−Li−Cu alloys independent of the other factors (such as matrix precipitate microstructure) that normally vary during aging treatments. For these experiments, the matrix precipitates of a binary Al−Li alloy were held constant, keeping the yield strength constant, while the GB precipitate size and volume percent were systematically varied. In contrast, to keep the yield strength of the ternary Al−Li−Cu alloy constant at the same level as the binary alloy, the matrix precipitate size and distribution were varied with the GB precipitate size.