Effect of Al matrix stacking sequences on T₁/Al interfacial stability and mechanical properties in Al–Li–Cu alloys: A first-principles study

Third-generation aluminum–lithium–copper (Al–Li–Cu) alloys are vital in aerospace applications, where the interface between precipitates and the metal matrix significantly affects mechanical properties. The structural difference between the T₁ phase (with 5R CDEDC stacking) and Al matrix (with 3R ABC stacking) makes the matrix stacking sequences particularly important for interface mechanical properties. However, previous research has often oversimplified this by considering only one matrix configuration. We used density functional theory (DFT) to analyze the stability of the hexagonal T₁ phase and nine different T₁/Al interfaces with varying matrix stacking sequences. By combining data from four databases, we created an updated Al–Li–Cu phase diagram that confirms T₁ phase stability, which we further validated through elastic constant calculations. Our results show that the B/T₁/A interface configuration is most stable, matching experimental findings. The impact of different matrix stacking sequences on interfacial energy (0.93 J/m²) proved significantly larger than previously reported effects of T₁ terminations (0.32 J/m²). Tensile testing revealed that interface strength correlates with adhesion energy, while matrix stacking sequences influence both mechanical properties and fracture behavior. These findings provide valuable insights for improving Al–Li–Cu alloy design and demonstrate the importance of considering matrix stacking sequences in future research on precipitation-strengthened alloy interfaces.