Effects of precipitates and solute atoms on the work hardening and softening behavior of Zn-rich aluminum alloy

In this paper, “AE” alloy with massive precipitates and “AS” alloy with high solute atom content were obtained by extrusion and solution treatment of Zn-rich aluminum alloy (Al–12Zn-2.4Mg-1.1Cu). The microstructure, mechanical properties, work hardening and softening behavior of the alloys were analyzed respectively. The results show that the “AE” alloy has fine grains and high precipitate content. After solution treatment, the grain size of “AS” alloy increases sharply, and the precipitates dissolve gradually. However, both elongation and strength increased significantly. After solution treated at 480 °C, the “AS-480″ alloy has a good combination of elongation (El) of 16.5% and ultimate tensile strength (UTS) of 619 MPa, indicating that the contribution of solute atoms is greater than that of grain boundary or precipitate. The work hardening capacity and work hardening index of “AE” alloy is higher than that of “AS-480” alloy. The effect of precipitates on work hardening behavior is more significant than solute atoms. When the strain exceeds 5%, the pinning effect of precipitate on dislocations leads to the decrease of softening degree and early failure. The influence of solute atoms on dislocations is weaker than that of precipitates, resulting in the continuation of softening and hardening behavior for “AS-480” alloy.