**4. Recrystallization of Mg alloys**

14 Recent Developments in the Study of Recrystallization

V45, and (f) V90 at a deformation rate of 0.0069/s.

(a) (b) (c)

(d) (e) (f)

**Figure 15.** Flow curves obtained from ZK60 alloys. (a) V0, (b) V45, and (c) V90 at a deformation rate of 0.139/s. (d) V0, (e)

The flow curves obtained during the uniaxial compression of the ZK60 alloys along the vertical direction are shown in Fig. 15. There are some differences between a high strain rate (0.139/s) and a low strain rate (0.0069/s). For a low strain rate of 0.0069/s, low temperatures of 298 K (25 ◦C) and 398 K (125 ◦C) were additionally assessed. The low temperatures cannot provide enough deformation modes, and the elongation at the temperatures is less than it is at other temperatures. The high strain rate of 0.139 imparts higher strength than that at the low strain rate of 0.0069. At a temperature of 448 K (175 ◦C), it is clear that a strain of 0.0069 shows more extended elongation than a strain of 0.139. The flow curves in Fig. 15(a) correspond to the microstructures examined above in Figs. 10 and 12. The samples taken from the different direction respond differently to external loading or compression. The samples referred to as V0 show the most dominant twinning; thus, some stress relaxation occurs during hardening (Figs. 15(a) and 15(d)). The samples termed V45 revealed some linear strain-hardening behavior (Figs. 15(b) and 15(e)). The samples referred to as V90 demonstrated typical non-linear strain-hardening behavior of the type usually found during the plastic deformation of polycrystalline materials (Figs. 15(c) and 15(f)). Note the curvature of the non-linear strain-hardening regions in the flow curves between V0 and V90. The former

Other flow curves obtained along the horizontal direction are shown in Fig. 16. At a high temperature of 498 K, the elongation is better than it is at a low temperature of 448 K. The strain-hardening behaviors of all samples measured from the horizontal directions, H0, H45, and H90, are similar to those of V0, as shown in Fig. 15(a). All show negative curvature during strain hardening, which implies that strong twinning occurred during warm compression.

shows negative curvature, while the latter shows positive curvature.

The recrystallization behavior of magnesium alloys was investigated during warm rolling and the subsequent annealing processes. Usually, plastic works of magnesium alloys, including rolling, extrusion, and forming processes, are performed at elevated temperatures. In the previous section, uniaxial compression carried out at various elevated temperatures was discussed. During the warm processing of the samples, dynamic recrystallization can occur depending on the temperature and the total strain. The as-rolled sheets are usually annealed before the next forming process; thus, the texture and microstructure are expected to change. In this section, two different cases of recrystallization - dynamic recrystallization and static recrystallization - are presented. Static recrystallization at the shear band region is also discussed.
