Microstructure and mechanical properties of a rapidly-solidified and extruded Al-13.2Zn-2.5Mg −1.2Cu-0.2Zr alloy and its aging hardening response at 120 °C

Abstract

A novel Al-13.2Zn-2.5Mg-1.2Cu-0.2Zr alloy was prepared by melt spinning and extrusion, and then further strengthened by solution at 470 °C and artificial aging (AA) at 120 °C. A bimodal grain structure, consisting of strong <001> and <111> double fiber textures along extrusion direction, was obtained by homogenization at 450 °C for 30min, followed by hot extrusion at 450 °C. Precipitate-assisted dynamic recrystallization and the pinning effect of undissolved second-phase particles on grain coarsening play a key role in forming the bimodal grain structure together. As-extruded alloy realizes strength-ductility combination mainly due to the existences of bimodal grain structure, hard-oriented <001> and soft-oriented <111> textures and high-density precipitates. Further solution treatment promotes the dissolution of most second-phase particles, and subsequent AA induces the precipitation of higher density nano-sized η′-phase, resulting in a notable increase in strength. However, the coarsening of undissolved second-phase particles and the thickening of precipitate free zones near grain boundary lead to a notable loss in ductility. As a result, the peak-aged alloy shows a higher strength but a lower elongation as compared to the as-extruded alloy.