Unveiling the underlying mechanism of forming edge cracks upon high strain-rate rolling of magnesium alloy

doi:10.1016/j.jmst.2020.03.006

Abstract

Abstract:

In the current study, high strain-rate rolling (≥10 s ^-1) has been successfully employed to produce Mg-3Al-1Zn alloy sheets to a high reduction of 82% with a fine grain structure in a single pass. The underlying mechanism of forming primary and secondary edge cracks has been investigated. It is found that dynamic recrystallization (DRX) induced by subgrains tends to blunt cracks, while twinning-induced DRX is mainly observed around sharp crack tips. The motion of emitted dislocations from blunted cracks is inhibited by the DRX grain boundaries. This, on one hand, increases local work hardening, and on the other hand, causes stress concentration along grain boundaries especially in the triple junctions leading to the formation of secondary cracks.

Key words: Edge crack, Secondary crack, High strain-rate rolling, AZ31 magnesium alloy, Dynamic recrystallization

Biwu Zhu, Xiao Liu, Chao Xie, Jing Su, Pengcheng Guo, Changping Tang, Wenhui Liu. Unveiling the underlying mechanism of forming edge cracks upon high strain-rate rolling of magnesium alloy[J]. J. Mater. Sci. Technol., 2020, 50: 59-65.

Figures/Tables 5

Fig. 1. Microstructures of the crack tips under different rolling conditions: (a1)-(a4) 300 ℃; (b1)-(b4) 350 ℃; (c1)-(c4) 400 ℃.

Fig. 2. Inverse pole figure maps, rotation axis distributions, misorientation distributions and KAM maps for the edge cracks of high strain rate rolled specimens at a temperature of 300 ℃ with different effective strain rates: (a1) Inverse pole figure map at 10 s-1; (b1) KAM map at 10 s-1; (c1) Misorientation angle distribution and rotation axis distribution for area A at 10s-1; (a2) Inverse pole figure map at 15 s-1; (b2) KAM map at 15 s-1; (c2) Misorientation angle distribution and rotation axis distribution for area B at 15 s-1; (a3) Inverse pole figure map at 20 s-1; (b3) KAM map at 20 s-1; (c3) Misorientation angle distribution and rotation axis distribution for area C at 20 s-1; (a4) Inverse pole figure map at 29 s-1; (b4) KAM map at 29 s-1 ; (c4) Misorientation angle distribution and rotation axis distribution for area D at 29 s-1.

Fig. 3. Rotation axis distribution and misorientation angle distribution for Area F of Fig. 2(a1).

Fig. 4. TEM images in front of crack tips with different type of cracks and different magnifications at 350 ℃: (a1), (a2) Blunted crack (10 s-1) and (b1), (b2) Sharp crack (20 s-1).

Fig. 5. Schematic diagram for crack blunting and the generation and growth of secondary crack for the blunted crack tip.

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