The influence of aging time at 175 ℃ on the tensile strength(σb), elongation(δ) and microstructures of Al-Cu-Mn casting aluminum alloy after (540±5) ℃ solution treatment for 14 h were investigated. The results showed that, the suitable aging time range is from 3 h to 8 h, during which the tensile strength would be greater than 455 Mpa and at the same time the elongation would be greater than 8%, the peak value of σbreaches 480 MPa when the aging time is 5 h, the corresponding elongation is 8.2%. The aging time has a little influence on the tensile strength, because the main strengthening mechanism is the dispersion strengthening of precipitate phase θ′ in matrix and the second T phase in grains. The elongation decreases with the increase of aging time, moreover, when the aging time is greater than 10 h, the elongation would be lowered distinctly and the value is less than 5.0%. The reason could be attributed to the fact that when the aging time is greater than 10 h, the appearance of Grain Precipitates on Boundary(GPB) changes from chain to bulky block, the Precipitation Free Zone(PFZ) is widened excessively, serious segregation of second T phase and blank area happens within grains, the matrix separated by the net-type grain boundary. All of above mentioned microstructures reduce the ductility of Al-Cu-Mn casting aluminum alloy.
