Abstract: Alumina reinforced aluminum matrix composites with different Al2O3 content were prepared with powder metallurgy and vacuum hot pressing sintering. The effects of microstructure and morphology on hardness of the composites were analyzed by X-ray diffraction，metallographic microscope and scanning electron microscopy. The results showed that with the increase of Al2O3 ranging from 1% to 4%，the hardness of the composites increased firstly and then decreased. When Al2O3 remained 2%，the sintering temperature was 400 ℃ and the pressure was 50 MPa，the hardness of the composites reached the highest of 38. 7 HV. It could be found in XRD patterns and metallographic pictures，the increasing hardness was attributed to the addition of Al2O3，which led to refining of the grain size and the microstructure of Al matrix.

Key words: vacuum hot press sintering, aluminum matrix composites, hardness, XRD, metallurgical structure