Cyclic deformation and fatigue of extruded AZ31B magnesium alloy under different strain ratios

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:649

Article

Xiong, Ying¹  Yu, Qin²  Jiang, Yanyao² 

[1] Zhejiang Univ Technol, Coll Mech Engn, Hangzhou 310032, Zhejiang, Peoples R China

[2] Univ Nevada, Dept Mech Engn, Reno, NV 89557 USA

关键词: Magnesium alloy;    Twinning;    Strain ratio effect;    Fracture;    Fatigue life;   

DOI  :  10.1016/j.msea.2015.09.084

来源: Elsevier

【 摘 要 】

Cyclic deformation and fatigue behavior of extruded AZ31B magnesium (Mg) alloy were investigated under strain-controlled loading along the extrusion direction at different strain amplitudes with three strain ratios (R-epsilon=0, -1, -infinity). With a strain ratio of R-epsilon= -infinity, partial twinning-partial detwinning occurs at all strain amplitudes, leading to accumulation of deformation twins as the loading cycle is increased. With strain ratios being R-epsilon = 0 and -1, partial twinning-complete detwinning is the cyclic deformation mechanism when the strain amplitude is higher than 0.35%. At a strain amplitude lower than 0.35%, dominant cyclic deformation mechanism is dislocation slips irrespective of the strain ratio. Compared with the cases of R-epsilon = 0 and R-epsilon= -1, stronger cyclic hardening is exhibited at all the investigated strain amplitudes for R-epsilon= -infinity. Fatigue fracture surfaces show regions with lamellar-like and dimple-like features. Lamellar-like feature existing in the crack initiation and stable propagation region are mainly due to twinning-detwinning during cyclic deformation. The dimple-like feature formed in the unstable crack propagation and final rupture region mainly arises from severe intra-granular plastic deformation by dislocation slips. At the same strain amplitude, the lamellar-like traces become more aggravated with a lower stain ratio. The strain-fatigue life curves exhibit a distinguishable kink at strain ratios R-epsilon = -infinity, -1 and 0. The fatigue life with R-epsilon = -infinity shows the highest and that with R-epsilon= 0 is the lowest at the same strain amplitude. The Smith-Watson-Topper (SWT) fatigue criteria can correlate well the fatigue experiments of AZ31B Mg alloy under different strain ratios. (C) 2015 Elsevier B.V. All rights reserved.

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