Using the synergistic role of intermetallics and multiple solute segregation at θ' interfaces to stabilise the microstructure of Al-Cu-Mn-Ni-X alloy at elevated temperatures

High-strength aluminum alloys often experience strength degradation at medium and high temperatures due to the rapid coarsening of nano-precipitates, which limits their application. The current research has enhanced the thermal stability of Al-Cu-Mn-Ni alloy through a high density of θ ' precipitates, T-Al 20 Cu 2 Mn 3 , Al 7 Cu 4 Ni, Al 3 (Cu, Mn) 2 intermetallics and dispersoids. Small amounts of Sc, Zr, and Ti are added to form multiple interface structures, including core-shell L1 2 -ordered Al 3 (Sc, Zr, Ti) dispersoids and a newly identified Al 3 (Ti, Mn) particles associated with θ ' plates. L1 2 -ordered core-shell dispersoids significantly refine θ' plates by acting as preferential nucleation sites for the L1 2 /matrix interfaces and segregation of Sc, Zr, Ti, Mn, and Ni at the θ ' /matrix interface is observed in the T6-treated alloy. Thermal stability of the Al-6Cu-0.5Mn-2Ni-0.4Zr-0.2Ti-0.25Sc alloy is studied at 250°C and 300°C. The peak hardness of the alloy is ~ 146 HV, with only a 23% reduction in hardness observed after 100 h of exposure at 300 o C. The modified Lifshitz-Slyozov-Wagner (LSW) model indicates a significantly lower coarsening rate for θ ' plates in the alloy being 10 3 times lower for length and 10 2 times lower for thickness compared to heat-resistant Al-Cu alloys reported in the literature. The low coarsening rate is attributed to the presence of multiple solute segregation layers around θ ' plates that inhibit Cu diffusion, slowing the coarsening of θ ' precipitates. This study demonstrates that multiple solute additions effectively enhance the thermal stability of the main strengthening precipitates during thermal exposure, a promising approach for developing heat-resistant engineering alloys. • Al-6Cu-0.5Mn-2Ni-Sc-Ti-Zr alloy retains 77% hardness after 100 h at 300°C • Thermal stability improves via GB intermetallic, and θ' and L1 2 precipitates • Core-shell L1 2 -Al 3 (Sc,Zr,Ti), Al 3 (Ti,Mn) act as preferential θ′ nucleation sites • Synergistic segregation at θ′/α-Al and T/α-Al interfaces stabilizes the alloy • θ' coarsening is reduced by 10 3 and 10 2 times in length and thickness