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 (eta) particles was the primary factor that determined the depths of age hardening layer. The eta 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.%). (C) 2011 Elsevier B.V. All rights reserved.