The microstructure and mechanical properties of Al-4.5wt%Cu alloy reinforced with diferent volume fractions(1.5vol%,3vol%,and 5vol%)of alumina nanoparticles,fabricated using stir casting method,were investigated.Calculated amounts of alumina nanoparticles(aboutφ50 nm in size)were ball-milled with aluminum powders in a planetary ball mill for 5 h,and then the packets of milled powders were incorporated into molten Al-4.5wt%Cu alloy.Microstructural studies of the nanocomposites reveal a uniform distribution of alumina nanoparticles in the Al-4.5wt%Cu matrix.The results indicate an outstanding improvement in compression strength and hardness due to the efect of nanoparticle addition.The aging behavior of the composite is also evaluated,indicating that the addition of alumina nanoparticles can accelerate the aging process of the alloy,resulting in higher peak hardness values. The microstructure and mechanical properties of Al-4.5 wt% Cu alloy reinforced with diferent volume fractions (1.5 vol%, 3 vol%, and 5 vol%) of alumina nanoparticles, fabricated using stir casting method, were investigated. Calculated amounts of alumina nanoparticles nm in size) were ball-milled with aluminum powders in a planetary ball mill for 5 h, and then the packets of milled powders were incorporated into molten Al-4.5 wt% Cu alloy. Microstructural studies of the nanocomposites reveal a uniform distribution of alumina nanoparticles in the Al-4.5 wt% Cu matrix. The results of an outstanding improvement in compression strength and hardness due to the efect of nanoparticle addition. The aging behavior of the composite is also evaluated, indicating that the addition of alumina nanoparticles can accelerate the aging process of the alloy, resulting in higher peak hardness values.