Effects of Sm element addition on the workability and microstructure evolution of Mg-Gd-Y-Zr alloy during hot deformation

A new Mg-5.5Gd-3Y-1Sm-0.5Zr (1Sm) alloy was developed. The deformation behavior and microstructure evolution of the Mg-Gd-Y-(Sm)-Zr alloys during hot compression were investigated systematically. The effects of Sm element addition on the workability and dynamic recrystallization (DRX) behavior of the Mg-5.5Gd-3Y-0.5Zr (0Sm) alloy was revealed. Sm element will increase the thermal activation energy and reduce the discontinuous dynamic recrystallization (DDRX) at 350 °C and 400 °C. The Mg5(Gd)-type phases are precipitated dynamically in the Mg matrix during low-temperature deformation process, and recrystallization occurs near the precipitated phase particles. At 450 °C and 500 °C, the continuous dynamic recrystallization (CDRX) is more prone to occur in the 1Sm alloy due to the high accumulation of misorientation angles in the initial coarse grains, so the DRX fraction of 1Sm alloy is higher than that of the 0Sm alloy. Furthermore, it is found that Sm element can weaken the basal texture. The intensity of the basal texture of the DRX grains of 1Sm alloy is lower than that of the 0Sm alloy at any temperatures. Based on the processing map, the optimum hot forming parameters of the 1Sm alloy is defined as temperature range 450–500 °C and strain rate range 0.01–0.1 s −1

Effect of strain rate on dynamic recrystallization mechanism of Mg-Gd-Y-Sm-Zr alloy during hot compression

Strain rate plays an important role in the hot deformation process of materials. In this work, hot compression experiments were conducted on Mg-Gd-Y-Sm-Zr alloy at the strain rates of 0.001–1 s−1 by Gleeble thermal simulation machine. The deformation behavior and microstructure evolution were studied in detail, and the dynamic recrystallization (DRX) mechanism was discussed. The results show that the flow stress of the alloy increases with the increasing strain rate. Deformation bands (DBs) are formed inside some grains at the strain rates of 0.1–1 s−1, which increase interfaces in the microstructure and hinder the dislocation movement. DRX grains are formed at the regions of DBs and original high angle grain boundaries (HAGBs). The DRX mechanism at high strain rates includes DBs induced DRX and discontinuous dynamic recrystallization (DDRX). At low strain rates and small strain, the dislocations first accumulate at the original HAGBs, and DDRX occurs in the alloy. The subgrains with low angle grain boundaries (LAGBs) are formed inside the initial grains through sufficient dynamic recovery (DRV) as strain increases, and LAGBs will gradually transform into HAGBs with the increasing misorientation angle. The DRX mechanism shows the synergistic effect of DDRX and continuous dynamic recrystallization (CDRX) at low strain rates