The effects of the content of coarse aluminum grains on the mechanical properties of nano-Al

2

O

3 p

/7075 aluminum-based composites were investigated. Fine powder（～5 μm） of 7075 alloy and nanometer Al

2

O

3

particles were high-energy ball milled through powder metallurgy method

and mixed with 7075 coarse aluminum particles of 0～15% for ordinary ball milling. After compacting and vacuum sintering and finally extrusion

the composites were fabricated. The compressive properties and hardness of the composites were tested at room temperature. The results indicate that as the content of coarse grains increases

the compressive strength of the composites is slightly decreased

while the elongation is increased obviously

where the compressive strength and hardness of composite containing 15% coarse grain are 5.0% and 7.2% lower than those of one without coarse grains

respectively

while the elongation is 27.6% higher. Therefore

the plasticity of composites is improved obviously by adding hierarchical structured composites that are manufactured by adding coarse matrix particles into nano ceramic particles reinforced aluminum matrix composites.