Mechanical Behavior and Microstructure Evolution of a Rolled Magnesium Alloy AZ31B Under Low Stress Triaxiality

doi:10.1016/j.jmst.2016.10.006

Abstract

Abstract:

Plastic deformation up to final rupture failure of a rolled magnesium (Mg) alloy Mg-3.0Al-1.0Zn-0.34Mn (AZ31B) under low stress triaxiality was investigated. Local strain evolution was quantified by the digital image correlation (DIC) technique analysis with tensile, combined tensile-shear, and shear specimens, corresponding to the stress triaxiality of 1/3, 1/6 and 0, respectively. Stress-strain curves show that the yield stress reduces with the decrease in the stress triaxiality, and obviously exhibits different strain hardening response. Electron backscatter diffraction (EBSD) observations reveal that the twinning behavior depends on stress triaxiality. Before fracture, double twinning is the dominant mechanism at the stress triaxiality of 1/3, while extension twinning is prevalent at the stress triaxiality of 0. Moreover, scanning electron microscopy (SEM) shows that the fracture mechanism is transformed from micro-void growth and coalescence to internal void shearing as the stress triaxiality decreases from 1/3 to 0.

Key words: Magnesium alloy, Stress triaxiality, Twinning

Pan Hongchen,Wang Fenghua,Jin Li,Feng Miaolin,Dong Jie. Mechanical Behavior and Microstructure Evolution of a Rolled Magnesium Alloy AZ31B Under Low Stress Triaxiality[J]. J. Mater. Sci. Technol., 2016, 32(12): 1282-1288.

Figures/Tables 9

Fig. 1. (a) Inverse pole figure (IPF) map, (0002) and (10-10) pole figures (PF) on the RD-TD plane and (b) test specimens with various geometries and shapes of rolled AZ31B alloy.

Fig. 2. (a) Engineering stress-strain curves and (b) strain distribution on the specimens T, ST, and S just before fracture analyzed by DIC.

Fig. 3. IPF maps of sample T: (a) at the strain of 2.0%, (b) at the strain of 4.0%, (c) after fracture. The {10-12} extension twin boundaries (86° <1-210> ±5°) are shown in red, the {10-11} contraction twin boundaries (56° <1-210> ±5°) in green and the {10-11}-{10-12} double-twin boundaries (38° <1-210> ±5°) in blue.

Fig. 4. IPF maps of sample S: (a) at the strain of 2.0%, (b) at the strain of 4.0%, (c) after fracture. The {10-12} extension twin boundaries (86° <1-210> ±5°) are shown in red, the {10-11} contraction twin boundaries (56° <1-210> ±5°) in green and the {10-11}-{10-12} double-twin boundaries (38° <1-210> ±5°) in blue.

Fig. 5. IPF maps of sample ST: (a) at the strain of 2.0%, (b) at the strain of 4.0%, (c) after fracture. The {10-12} extension twin boundaries (86° <1-210> ±5°) are shown in red, the {10-11} contraction twin boundaries (56° <1-210> ±5°) in green.

Fig. 6. Misorientation angle distributions of samples at different strains: (a) T sample, (b) S sample, (c) ST sample.

Fig. 7. Twin volume fraction (TVF) developed with increasing the plastic strain (Horizontal axis is logarithmic).

Fig. 8. Schematic of the proposed mechanism for the different deformations: (a) tension, (b) compression and (c) shear loading.

Fig. 9. Fracture surface of the samples under different stress triaxiality: (a) 1/3 (sample T), (b) 0 (sample S) and (c) 1/6 (sample ST).

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