Acceleration of aging behavior and improvement of mechanical properties of extruded AZ80 alloy through (10–12) twinning

Abstract

The effects of pre-existing {10–12} extension twins on the precipitation behavior of an extruded AZ80 material during aging and on its mechanical properties after peak aging are investigated. The material containing {10–12} twins—which are formed by compression before aging (twinned material)—has a finer grain size and higher dislocation density than the extruded material. Although the peak hardnesses of the twinned and extruded materials are almost the same, the time to reach the peak hardness is considerably shorter in the former material than in the latter (4 h and 24 h, respectively). In the twinned material, the high dislocation density of the {10–12} twins promotes continuous precipitation, which results in the formation of numerous fine Mg17Al12 precipitates within the twins in the early stage of aging. The formation of these continuous precipitates reduces the driving force for discontinuous precipitation, which consequently suppresses the formation and growth of coarse Mg17Al12 precipitates at the grain boundaries. Despite its shorter peak-aging time, the 4 h-peak-aged twinned material shows higher tensile strength and elongation than the 24 h-peak-aged extruded material. These higher mechanical properties of the former material are attributed primarily to the presence of more abundant fine continuous precipitates, which are effective in strengthening the material, and less abundant coarse discontinuous precipitates, which can act as crack initiation sites. These results demonstrate that the introduction of {10–12} twins into wrought Mg–Al-based alloys can accelerate the Mg17Al12 precipitation kinetics considerably and improve the strength and ductility of the peak-aged alloys simultaneously.

Keywords

• AZ80 alloy
• Twin
• Aging
• Precipitation
• Tensile properties