Microstructures and mechanical properties of a cast Al–Cu–Li alloy during heat treatment procedure

Abstract

Al–Cu–Li alloy is a huge potential alloy for aerospace industry due to its low density and excellent comprehensive performances. In this study, the microstructures and mechanical properties of a novel cast Al–Cu–Li alloy during the heat treatment were investigated. Results showed that most of the secondary phases along grain boundaries in as-cast state were dissolved into the Al matrix after homogenization and solution treatment, while the Cu-rich phases were slightly segregated once again on grain boundaries after aging. A relatively good combination of strength and ductility (average ultimate tensile strength of 430 MPa and elongation of 8.9%) was obtained after natural aging. Transmission electron microscopy (TEM) results revealed that there was a complicated precipitate distribution in this cast alloy after natural aging. Compared with the similar alloys which introduced dislocations before aging, the density of T1 (Al2CuLi) phases was decreased but the size was increased. The low volume fraction of δ′ phase, medium density of needle-shaped precipitates and relativity narrow precipitates-free zone with varying widths near grain boundary are the reasons accounting for the improvement of performances.