Highly stable coherent nanoprecipitates via diffusion-dominated solute uptake and interstitial ordering.

Abstract

Lightweight design strategies and advanced energy applications call for high-strength Al alloys that can serve in the 300‒400 °C temperature range. However, the present commercial high-strength Al alloys are limited to low-temperature applications of less than ~150 °C, because it is challenging to achieve coherent nanoprecipitates with both high thermal stability (preferentially associated with slow-diffusing solutes) and large volume fraction (mostly derived from high-solubility and fast-diffusing solutes). Here we demonstrate an interstitial solute stabilizing strategy to produce high-density, highly stable coherent nanoprecipitates (termed the V phase) in Sc-added Al-Cu-Mg-Ag alloys, enabling the Al alloys to reach an unprecedented creep resistance as well as exceptional tensile strength (~100 MPa) at 400 °C. The formation of the V phase, assembling slow-diffusing Sc and fast-diffusing Cu atoms, is triggered by coherent ledge-aided in situ phase transformation, with diffusion-dominated Sc uptake and self-organization into the interstitial ordering of early-precipitated Ω phase. We envisage that the ledge-mediated interaction between slow- and fast-diffusing atoms may pave the way for the stabilization of coherent nanoprecipitates towards advanced 400 °C-level light alloys, which could be readily adapted to large-scale industrial production.