The Microstructure And Mechanical Properties Of Al-Cu-Mg-(Ag)Alloys

(1) The aging hardening response of the studied Al-Cu-Mg-Ag alloys was accelerated as the Ag content increased from0.14%to0.57%. The mechanical properties at various temperatures also exhibited the similar trend.(2) The increasing Ag content was found to be beneficial to the stability of Ω phase and promote the dense precipitation of Ω. phase, thereby suppressing the formation of0’phase.(3) The hardening curve of2524alloy aging at170℃showed two hardening stages. The hardness of as-quenched2524alloy increased rapidly from89.2HV to122.1HV after a short term aging. After10h aging, the second hardening occurred and reached the maximum hardness of145.7HV at75h.(4) The highest number density of Cu-Mg co-clusters with small size was revealed in2524-T4alloy. During the aging process at170℃, the main strengthening precipitates and corresponding percentages varied. After aging for5min, Cu-Mg co-clusters dominated the microstructure. After aging for1to8h, the formation of GPB zones was observed but its percentage remained constant. GPB zones dominated the microstructure after aging for12h. In peak aged condition, the precipitation of S(S’) phase was confirmed,. Also, the size of GPB zones greatly increased, whereas the number density of Cu-Mg co-clusters sharply decreased.(5) The precipitation sequence in2524alloy during aging at170℃was:SSSâ†'Cu-Mg co-clustersâ†'Cu-Mg co-clusters+GPB zonesâ†'Cu-Mg co-clusters+GPB zones+S(S’)â†'S.(6) The Cu/Mg ratio and elastic modulus of Cu-Mg co-clusters showed a linear relationship with the aging time, and increased slowly with the increasing aging time. The trend of shear stress caused by modulus hardening was consistent with the hardening curve.(7) The specimen aged at170℃for1h exhibited a better fatigue resistance than that of T4temper. T After aging at170℃for8h, the worst fatigue resistance was revealed.