Effect of {10–12} Twins on Precipitation Behavior of Extruded Mg–8Al–0.5Zn Alloy During Low-temperature Aging

Abstract

This study investigates the influence of {10–12} twins on the aging behavior of an extruded Mg–8Al–0.5Zn (AZ80) alloy during aging at 150 °C. The extruded AZ80 alloy is subjected to a compressive strain of 6% along the transverse direction and is subsequently aged at 150 °C. The sample with {10–12} twins (referred to as the twinned sample) exhibits a finer grain size and higher internal strain energy compared to the extruded sample. The peak-aging time of the twinned sample is 32 h, which is significantly shorter than that of the extruded sample without twins (200 h). Moreover, the peak-aged hardness of the twinned sample (96.3 Hv) is slightly higher than that of the extruded sample (93.6 Hv), despite the substantially shorter peak-aging time in the former. The high internal strain in the twinned sample, especially within the twins, promotes the formation of continuous precipitates (CPs) during the early stages of aging. As the aging time increases, the number density of fine CPs in the twins increases through additional precipitation. In the extruded sample, the area fraction of discontinuous precipitates (DPs) rapidly increases with increasing aging time. In contrast, the formation and growth of DPs are substantially suppressed in the twinned sample, because CPs predominantly form and twin boundaries act as barriers to DP growth. As a result, the area fraction of the peak-aged twinned sample (5.1%) is significantly lower than that of the peak-aged extruded sample (60.2%). Consequently, the introduction of {10–12} twins in the extruded AZ80 alloy results in the promotion of CP formation, suppression of DP formation, and significant reduction in peak-aging time under the 150 °C aging condition.