Microstructure and hot deformation behavior of a new aluminum–lithium–copper based AA2070 alloy

Abstract

The effects of initial microstructure on hot compression behavior of a new Al–Li–Cu alloy AA2070 were studied in the temperature range of 250 °C–450 °C and strain rate range of 0.001 s−1 - 0.1 s−1. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize microstructure prior to and post deformation. Two types of major strengthening precipitates were identified: Al2CuLi (T1) phase with habit planes parallel to {111}Al and Al2Cu/Al3Li (Ɵ'/δ′) composite precipitates with habit planes parallel to {100}Al, in the initial microstructure. The combination of these precipitates provides strong resistance to dislocation slip. While dynamic recovery is the main softening mechanism at compression temperatures below 450 °C, dynamic recrystallization dominates softening at 450 °C. T1 precipitate bands consisting of multiple fine T1 precipitates exist in microstructure after hot deformation at 250 °C and 350 °C. The formation mechanisms of T1 precipitate bands and fine T1 precipitates are discussed in light of shearing deformation of T1 precipitates. After hot deformation at 350 °C, Ɵ'/δ′ composite structure is lost and only Ɵ′ precipitates exist in the post-deformation microstructure. The interface between Ɵ′ precipitate and aluminum matrix becomes incoherent. The optimal processing conditions of this alloy have been identified as a temperature of 450 °C and a strain rate of 0.001 s−1, with significant grain refinement and the weakest deformation texture, which are consistent with the analysis results of hot work efficiency and instability using pseudo processing maps.