Influence of Mg content on quench sensitivity of Al–Zn–Mg–Cu aluminum alloys

The influence of Mg content on quench sensitivity of Al–8.0Zn–x(=1.0–2.0)Mg–1.6Cu alloys was investigated by an end-quenching test method. The depths of age hardening layer referenced to hardness retention values (e.g., 90%) of the end-quenched samples were used to describe the quench sensitivity. The results showed that the depths of age hardening layer decreased with increase of Mg content. The amount of the equilibrium-state MgZn2 (η) particles was the primary factor that determined the depths of age hardening layer. The η particles underwent two precipitation processes successively with decrease of cooling rate during quenching: precipitation on grain boundaries and precipitation inside the grains. The precipitation temperature peaks rose, and the ranges of the temperatures are extended with the increase of Mg content. A preliminary prediction has been made for the initial precipitation temperatures and the temperature peaks satisfying linear relation with Mg content (wt.%).

Research highlights
► The end-quenching test is easy to reveal the quench sensitivity of Al–Zn–Mg–Cu aluminum alloys.
► The η particles undergo two precipitation processes successively during quenching: precipitation on grain boundaries and precipitation inside the grains.
► The quench sensitivity of Al–Zn–Mg–Cu aluminum alloys is influenced by the Mg content observably.