The Influence of the Zn/Mg Ratio on the Quench Sensitivity of Al-Zn-Mg-Cu Alloys

The effects of the Zn/Mg ratio on the precipitate behavior and mechanical properties of Al-Zn-Mg-Cu alloys at different quenching rates were investigated by a Jominy end-quench test, tensile test and microstructural analysis. The results show that the hardness and strength of the aged alloys clearly decrease with increasing quenching distance (D). Additionally, the alloy with a Zn/Mg ratio of 5.42 has a more obvious drop in yield strength than the alloy with a higher ratio of 7.09 when D is varied from 10 mm to 142 mm. During slow quenching, fewer equilibrium η phases are formed in the alloy with a higher Zn/Mg ratio of 7.09, and then a larger number of fine η′ phases precipitate during subsequent aging, which reduces the quench sensitivity of the alloy.