Enhancing strength-ductility synergy in an extruded Al-Cu-Li-Mg-Ag alloy via homogeneous GP zones and dislocation configuration

Abstract

Balancing strength and ductility proves challenging in high-strength wrought Al-Cu-Li alloys, particularly in extruded rods. The abundance of subgrain structures hinders dislocation movement, inevitably sacrificing the ductility. Herein, an effective strategy for enhancing the strength-ductility synergy in an extruded Al-3.7Cu-1Li-0.40Mg-0.75Ag alloy was reported by developing a novel combinatorial pretreatment (CPT), including pre-ageing after solution treatment, followed by pre-stretching. Subsequently, the CPT alloys undergo artificial ageing at 150 °C. Desirable comprehensive mechanical properties (YS = 668 MPa, UTS = 700 MPa, and EL = 12.5 %) were obtained through pre-ageing at 110 °C before 4 % pre-stretching. Notably, the elongation showed a remarkable improvement of 60.3 % compared to the non-CPT sample, without sacrificing the yield strength. Microstructure analysis indicates that the interactions between the GP zones and dislocations facilitated energy dissipation during pre-stretching, effectively mitigating local stress concentration. Consequently, promoted ductility was realized through a more uniform dislocation distribution. Furthermore, the dense GP zones formed during pre-ageing served as the heterogeneous nucleation sites for precipitates, increasing the volume fraction of θ′ phases. This adjustment in dislocation motion further contributed to ductility improvements. Our approach offers new insights into developing high-performance extruded Al-Cu-Li alloys with both high strength and desirable ductility.