Achieving ultra-high performance after thermal exposure temperature for Al-Cu alloys by stabilizing nano θ′ precipitates and diversifying micro-compounds with Sc and Li

Al-Cu alloys are widely used on aircrafts due to their excellent fracture toughness and fatigue behaviour even at 200 °C. However, prolonged exposure at high temperature over 200 °C leads to rapid degradation of their strength, which limits their application on larger and faster airplanes. To overcome this limitation, this study designs an advanced Al-Cu-Li-Sc alloy, which incorporates not only such traditional transitional heat-resistant elements as Ti, Zr, Mn, and Cr, but also propose a new heat treatment strategy for Sc and Li alloying in order to stabilize nano θ′ precipitates and promoting the formation of micro-compounds at elevated temperatures. The addition of Li enhances the formation of a higher fraction of micron-scale secondary phases, including the co-segregation of Mn and Sc. The new Al-Cu-Li-Sc alloy demonstrates exceptional high-temperature performance, retaining a tensile strength of 302 MPa after 100 h of exposure at 300 °C, which substantially surpasses the performance of conventional Al-Cu-based alloys. The enhanced thermal resistance can primarily be attributed to the improved heat resistance of multi-scale phases within the alloy, as well as the unique three-dimensional orientation characteristics of nanophases with multi-configurational features. These factors collectively provide superior dislocation obstruction compared to single-phase strengthening mechanisms.