The effect of sintering time on synthesis of in situ submicron α-Al2O3 particles by the exothermic reactions of CuO particles in molten pure Al

► Al-Cu/Al2O3 composites were prepared successfully by means of hot pressing method. ► Sintering time of the Al-CuO system effect the reaction rate and formation of Al2O3. ► Increase in sintering time accelerates formation of submicron in situ α-Al2O3 phase. ► Hardness of the sintered composite for 30 min at 1000 °C increased from 60 to 174 HV.