The interactions between dynamic precipitates and dynamic recrystallization in Mg-5Zn-1Mn alloys during hot compression

Abstract The interactions between dynamic precipitates and dynamic recrystallization (DRX) in hot compressed ZM51 alloys with strain rates from 1 s−1 to 20 s−1 were carefully investigated by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The DRX grain size and the precipitate volume fraction decrease, while the DRX volume fraction increases with increasing the strain rate (T = 300 °C, e = 1.61). The proportion of β2′ phase is larger than that of β1′ phase, indicating that β2′ phase becomes the main precipitates at the later deformation stage. Grain boundary bowing is the main DRX mechanism at the strain rate of 1 s−1, while the twin-aided DRX mechanism dominates at the higher strain rates (έ ≥10 s−1). The DRX grain size, the volume fractions of the precipitates and DRX increase with increasing the strain (T = 300 °C, έ = 10 s−1). Increasing the strain didn't change the types of the precipitates, but led to the reduction of β1′ phase and the increase of β2′ phase. All the precipitates become spheroid. The higher DRX volume fraction with the lower precipitate volume fraction were detected at the higher strain rates (έ ≥10 s−1), while the situations at the lower strain rate (έ =1 s−1) were reverse. It is due to the fact that the precipitates can hinder the nucleation and growth of DRX because of their pinning effect on dislocations, twin boundaries, sub-grain boundaries and DRX grain boundaries. The precipitation sequence in the deformation process is more complex than that in the traditional aging process and the deformation accelerates the precipitation and phase transformation processes.