Abstract:The effect of the second phase precipitation behavior on the mechanical properties and fracture behavior of the modified casting Al-Cu alloys was investigated. The tensile strength of the alloys increases firstly and then decreases due to the appearance of θ′ precipitation phases, which increases firstly and then become coarser with the aging time increasing from 10 h to 20 h at 155 ℃. The strength of the alloys reaches the peak, resulting from Ω and θ′ precipitation phases, and decreases due to Ω phases becoming coarser and θ′ precipitation decreasing with the aging time increasing from 10 h to 20 h at 165 ℃. Ω phase becoming coarser and θ′ precipitation decreasing result in the strength of the alloys drastically decreasing after aging at 175 ℃ for 20 h. The ductility remains high level with increasing aging time at 155 ℃. The ductility irregularly changes as aging time prolongs at 165 ℃. The ductility is very low and at the same time gradually decreases with increasing aging time at 175 ℃. The Al-Cu alloy with a promising combination of tensile strength and ductility of about 474 MPa and 12.0% after aging at 165 ℃ for 10 h is due to a dense, uniform distribution of Ω precipitation phases together with a heterogeneous distribution of θ′ precipitations.

Key words: Al-Cu alloys; heat treatment; mechanical properties; precipitate