Ameliorating the microstructure and mechanical properties of Al-Cu-Li alloy through aging temperature in a novel thermo-mechanical treatment

Developing high-strength and ductility wrought aluminum-lithium alloys has been a longstanding objective in the aviation and aerospace industry. However, the conventional T8 thermo-mechanical treatment (TMT) process faces challenges in overcoming the strength-ductility compromise in aluminum-lithium alloys. The precipitates-dislocation interaction is critical in governing the balance between strength and ductility. When the aging temperature exceeds 175 °C, the T₁ phase thickens, making it difficult for slip dislocations to shear the coarser T₁ phase. This results in severe matrix distortion near the precipitates, thereby reducing ductility. In contrast, aging at 150°C promotes the formation of fine, shearable T₁ phases, facilitating uniform plastic deformation across multiple slip planes and achieving a balance of high strength (~705 MPa) and ductility (~11.8%). Aging at 120°C further improves ductility (~12.4%) due to the coexistence of sparse T₁ phases and large amounts of Guinier–Preston (GP) zones, which promoted dislocation cross-slip. Our findings highlight the critical importance of precisely controlling the relative amount, size, and distribution of GP zones and T₁ precipitates to achieve superior mechanical performance in Al–Cu–Li-Mg-Ag alloys.