Quench sensitivity of four Al-Zn-Mg-Cu aluminum alloys

Abstract:

The time-temperature-transformation(TTT) curves and CCT curves of four Al-Zn-Mg-Cu alloys were completed in the Al-based database of software JMatPro7.0 with the first principles. To conclude, for 7055 alloy with the highest gross amount of main alloying elements and highest Cu element content, TTT and CCT curves were at the top left. For 7085 alloy with the lowest Cu element content and highest Zn/Mg ratio, TTT and CCT curves were at the bottom right, thus the incubation of equilibrium phase precipitation was the longest, start precipitation temperature and the nose temperature were the lowest, and therefore the quench sensitivity was the lowest. For 7075 alloy with the lowest Zn/Mg ratio and the incoherent E (Al₁₈Cr₂Mg₃) phase within grains, the quench sensitivity was the highest. The results show that compared with the conductivity of as-quenched and hardness as-aged at 960℃/s, the conductivity difference and hardness drop rates for 7075,7055,7050,7085 four alloys cooled at 1.8℃/s were decreased and the hardness drop rates were 35.5%, 19%, 13.8% and 9.5% respectively. The lattice constant and the size and area fraction of the quench-induced phases for the four alloys cooled at 1.8℃/s reduced, and thus the quench sensitivity decreased.