Microstructural effects on quasi-static fracture mechanisms in AlLi alloys: the role of crack geometry

Abstract

The influence of aging treatment on fracture toughness was investigated in a high purity AlLiCuZr alloy. It was found that variations in microstructural features and slip characteristics induced by the tempering treatment give rise to marked differences in crack morphology among the aging conditions during quasi-static fracture. The underaged microstructures promote severely branched cracks during the onset of fracture and subsequent crack growth. In contrast with this, the overaged tempers tested at comparable yield strength levels result in a linear crack profile. Such differences in the local mode of crack advance seem to account for a significant proportion of the microstructural effects on fracture in this material. Accordingly, a crack-deflection-modified fracture toughness parameter is used to characterize the effects of microstructure on quasi-static fracture by incorporating local mixed-mode stress intensity calculations for the non-linear crack profiles developed in underaged structures. The role of crack deflection in the fracture of aluminum alloys is detailed and correlations between microstructure and deflection characteristics are explored.