Abstract: The secondary aging treatment (T6I4) is to change the aging temperature at the under-aging time point of single-stage aging, and carry out low temperature second-stage aging treatment on the alloy. The microstructure, mechanical properties and corrosion resistance of an Al-Cu-Mg alloy can be appropriately improved by the secondary aging treatment. The microstructures and properties of an Al-Cu-Mg alloy with the secondary aging were investigated by hardness measurement, exfoliation corrosion text, intergranular corrosion test, stress corrosion cracking test, observations through scanning electron microscope and transmission electron microscope. The experimental results show that the mechanical properties of an Al-Cu-Mg alloy aged at 170 ℃ for 2 h and then aged at 100 ℃ for 30 h are better than those of the traditional single-stage aging treatment and the corrosion resistance is also significantly improved, which due to the formation of fine and dispersed θ' phase in the crystal of an Al-Cu-Mg alloy and S phase θ' is uniformly distributed in the matrix after the secondary aging treatment. The tensile strength, elongation, Vickers hardness, exfoliation corrosion grade, intergranular corrosion depth and stress corrosion cracking index were 490 MPa, 8.5%, 156.3 HV_0.5, EA, 98.6 μm and 0.220, respectively.

Key words: Al-Cu-Mg alloy, secondary aging, microstructures, corrosion resistance