**4.2. Static recrystallization of warm-rolled AZ31B alloys**

The warm-rolled sheets show a mixture of large and small grains, as shown in Fig. 18. It appears that the initial large grains are shattered into various sizes of grains during the warm rolling process. During static annealing for 10 min at 573 K (300 ◦C), the as-rolled structure becomes a fully-recrystallized grain structure, with all grain shapes equi-axed. There exists some variation in the grain sizes of the annealed sheets. The overall textures of both the as-rolled and annealed sheets revealed similar basal fibers. The basal intensity of the as-roll

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(a)

(b)

(c) (d)

**Figure 18.** Band contrast maps of warm-rolled AZ31B sheets obtained by means of EBSD measurements. The grain identification angle (GID) is 15 ◦ with black lines. The step sizes of the as-rolled and annealed sheets are 0.25 µm and 0.5 µm, respectively. (a) band contrast, and (c) pole figures of the as-rolled sheets. (b) band contrast, and (d) pole figures of the annealed

sheet confirmed in the (0002) pole figures was stronger than that of the annealed sheet. The basal intensity distribution of the as-rolled sheet also illustrates a more compact distribution

Figure 19(a) shows the shear band of the AZ31B alloy, which formed during warm rolling at a temperature of 498 K (225 ◦C). The shear band region contains numerous twins, and its pole figure in Fig. 19(b) reveals a second strong area of intensity near the *X*<sup>0</sup> direction. The entire region shows a strong basal texture in Fig. 19(c) of the type usually found during the warm rolling of Mg alloys. The as-rolled sample was annealed for 20 minutes at 573 K (300 ◦C) and

sheets.

than that of the annealed sheet.

(a)

(c) (d)

(b)

**Figure 17.** Inverse pole figure (IPF) maps of hot-rolled AM31 alloys. Two different regions were measured using EBSD. The grain identification angle (GID) is 15 ◦ with thick black lines, and the GID is 2◦ as denoted by the thin black lines. The step size for the EBSD measurements is 0.5 µm. The thick red, blue and yellow lines represent the tensile, compressive, and double twin boundaries, respectively. (a) inverse pole figure map and (c) pole figures for the first region. (b) inverse pole figure map and (d) pole figures for the second region.

16 Recent Developments in the Study of Recrystallization

pole figures for the second region.

(a)

(b)

(c) (d)

**Figure 17.** Inverse pole figure (IPF) maps of hot-rolled AM31 alloys. Two different regions were measured using EBSD. The grain identification angle (GID) is 15 ◦ with thick black lines, and the GID is 2◦ as denoted by the thin black lines. The step size for the EBSD measurements is 0.5 µm. The thick red, blue and yellow lines represent the tensile, compressive, and double twin boundaries, respectively. (a) inverse pole figure map and (c) pole figures for the first region. (b) inverse pole figure map and (d)

**Figure 18.** Band contrast maps of warm-rolled AZ31B sheets obtained by means of EBSD measurements. The grain identification angle (GID) is 15 ◦ with black lines. The step sizes of the as-rolled and annealed sheets are 0.25 µm and 0.5 µm, respectively. (a) band contrast, and (c) pole figures of the as-rolled sheets. (b) band contrast, and (d) pole figures of the annealed sheets.

sheet confirmed in the (0002) pole figures was stronger than that of the annealed sheet. The basal intensity distribution of the as-rolled sheet also illustrates a more compact distribution than that of the annealed sheet.

Figure 19(a) shows the shear band of the AZ31B alloy, which formed during warm rolling at a temperature of 498 K (225 ◦C). The shear band region contains numerous twins, and its pole figure in Fig. 19(b) reveals a second strong area of intensity near the *X*<sup>0</sup> direction. The entire region shows a strong basal texture in Fig. 19(c) of the type usually found during the warm rolling of Mg alloys. The as-rolled sample was annealed for 20 minutes at 573 K (300 ◦C) and

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**5. Conclusion**

curvature.

**Acknowledgements**

Jae-Hyung Cho and Suk-Bong Kang

Y. *Acta Mater.*, 49:4277–4289, 2001.

*Mater. Sci. Eng., A*, 480:189–197, 2008.

**Author details**

**References**

The textural and microstructural evolution of wrought magnesium alloys of AZ31B, ZK60

• As-extruded AZ31B billets with extrusion fiber orientations show strong twinning during compression along the extrusion direction. Most of the grains went through twinning at a strain of approximately 3%, after which all became a twinned region at a strain of about 8%. As-warm rolled ZK60 alloys with a weak basal texture also show strong twinning during compression along the rolling direction. Both the as-extruded AZ31B and the warm-rolled ZK60 compressed samples were designed to experience c-axis tension during compression, allowing easy activation of tensile twinning. The flow curves revealed that tensile twinning clearly relaxed the strain-hardening behavior, as evidenced by negative

• The as-casted AM31 alloys with an initial random orientation show that the shear band can provide a useful mechanism to accommodate external loading. Inside large grains, many shear bands form and are recrystallized during the hot rolling process. The as-rolled AZ31B strips fabricated by twin roll casting possessed initial basal fibers that changed into identical basal fibers after full annealing. During the static annealing process, the deformed microstructure became an equi-axed and recrystallized grain structure. The shear band region with off-basal texturing provides off-basal textures

The authors would like to thank Lili Chang, Yinong Wang, Shou-ren Wang, Sang Su Jeong

[1] S. R. Agnew, M. H. Yoo, and C. N. Tome. Application of texture simulation to understanding mechanical behavior of Mg and solid solution alloys containing Li and

[2] J. Bohlen, M.R. Nurnberg, J.W. Senn, D. Letzig, and S.R. Agnew. The texture and anisotropy of magnesium-zinc-rare earth alloy sheets. *Acta Mater.*, 55:2101–2112, 2007.

[3] L.W.F. Mackenzie and M. Pekguleryuz. The influences of alloying additions and processing parameters on the rolling microstructures and textures of magnesium alloys.

during static annealing and contributes to lowering the basal texturing.

Korea Institute of Materials Science (KIMS), Light Metals Division, South Korea

and Hyoung-Wook Kim for their comments and help.

and AM31 was investigated during deformation and recrystallization.

(c)

**Figure 19.** Inverse pole figure maps of warm-rolled AZ31B sheets obtained by means of EBSD measurements. The grain identification angle (GID) is 15 ◦ with black lines. The step size is 0.5 µm. (a) inverse pole figure map, (b) pole figures of the shear bands only, and (c) pole figures of the whole region.

was then remeasured using EBSD (Fig. 20). Marked scratch lines were used for the ex-situ mapping. Although the overall region still revealed a basal texture after annealing, a much wider distribution in the basal texture was observed after annealing, as shown in Fig. 20(b), due to the off-basal orientations in the recrystallized shear band region.

**Figure 20.** Inverse pole figure masp of warm-rolled AZ31B sheets obtained by means of EBSD measurements. The grain identification angle (GID) is 15 ◦ with black lines. The step size is 0.5 µm. (a) inverse pole figure map, and (b) pole figures of the whole region.
