Effect of compositions on the quenching sensitivity of 7050 and 7085 alloys

The requirement for large aircraft components to have Al-Zn-Mg-Cu alloys with high strength and low quenching sensitivity has been increasing. The quenching sensitivity of 7085 and 7050 alloys used for thick plate applications was characterized via hardness tests and microstructure observation. A quenching precipitation model was established to predict the evolution of grain boundary and intragranular precipitates during air quenching process, and the effect of composition on the quenching precipitation behavior was investigated using this model. The quenching precipitation kinetic results show that the 7085 alloy has a low quenching sensitivity because the density of the precipitates in the Al3Zr dispersoids and at the grain boundary is lower compared with that of the 7050 alloy. This result is in agreement with experimental results. Furthermore, the thermodynamic calculation results illustrate that the increase in the Zn/Mg ratio and the decrease in Cu element cause the α phase region to expand, thereby reducing the quenching sensitivity of the 7085 alloy.