Evaluation Of The Quenching Sensitivity Of Al-Zn-Mg-Cu-Zr Aluminum Alloys By Mole Fraction Of Equilibrium Phases

The effect of composition on the quenching sensitivity of Al-Zn-Mg-Cu-Zr aluminum alloys was investigated through hardness test, microstructure analysis and thermodynamic calculations. The materials involved are 7085, 7050, 7150 and 7055 aluminum alloys. The quenching sensitivity of the alloys has been evaluated by the percentage of hardness reduction after aging process. The results show that the aging hardness reductions for the alloys by air quenching are up to 8.6%, 18.4%, 21%) and 21.7%, respectively, in comparison with that by water quenching. The precipitation of 7050 and 7055 aluminum alloys is much more compared to that of 7085 aluminum alloy during air quenching process, which decreases the capability of aging hardening and causes quenching sensitivity of 7050 and 7055 aluminum alloys. The interrelation of composition, equilibrium phase and quenching sensitivity is investigated from perspective of thermodynamic calculations, and the total mole fraction of equilibrium phase during quenching process is proposed to be a criterion for evaluating the quenching sensitivity of Al-Zn-Mg-Cu-Zr series aluminum alloys.