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. Graphic abstract: [Figure not available: see fulltext.]