Studies on thermal stability, softening behavior and mechanism of an ADS copper alloy at elevated temperatures

•An alumina dispersion strengthened copper alloy exhibits the highest softening temperature of 1203 K and was fabricated by in-situ internal oxidation and reduction method.•The strong pinning effect of the nanometer-scaled Al2O3 particles helps increase the dislocation density and the grain boundary stability even at elevated temperatures.•A modified Hall-Petch relationship was established by introducing the integration of the grain size distribution, which can describe the correlation between softening behavior and the pinning effect of Al2O3 particles.