Comparative study on the formability and microstructure evolution of different tempered Al–Cu–Li alloy sheets during room and cryogenic temperature forming process

Abstract

High strength aluminum alloy sheets with excellent formability are necessary for the successful fabrication of complex-shaped components in order to prevent cracking during the forming process. To address this issue, this study investigated the formability of annealed (O) and water-quenched (WQ) Al–Cu–Li alloys at both room and cryogenic temperatures. Our results reveal a significant increase in the forming limit curve, with a 40% enhancement observed as the forming temperature decreased from 298 K to 113 K. Additionally, a 30% increase in formability was observed when transitioning from the O temper to the WQ temper. Thickness measurements reveal that WQ pre-treatment and cryogenic forming promoted continuous work hardening, thus improving deformation homogeneity. The mechanism responsible for the higher work hardening ability was elucidated by examining the microstructure evolution in different regions of the components. The results show that coarse particles in the O tempered alloys accelerated cross slip, resulting in the formation of recovered microstructures (i.e., dislocation cells and Cube texture) while simultaneously hindering dislocation movement and inducing local stress concentration. Conversely, for the WQ tempered alloy deformed at cryogenic temperature, the dissolution of particles and decreased stacking fault energy at low temperature suppressed cross slip and resulted in well-arranged dislocations within the slip system. Consequently, the combination of WQ pre-treatment and cryogenic forming demonstrates enhanced formability in high strength aluminum alloys, offering a novel method for manufacturing complex-shaped components.

Keywords

• Al–Cu–Li alloys
• Formability
• Cryogenic temperatures
• Microstructures