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

Developing wrought aluminum-lithium alloys with high strength and ductility has been a longstanding objective in the aviation and aerospace industry. However, the conventional T8 thermo-mechanical treatment 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.