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

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• 作者：Ying Xiong^a ; Qin Yu^b ; Yanyao Jiang^b ; ^{yjiang@unr.edu" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Magnesium alloy ; Twinning ; Strain ratio effect ; Fracture ; Fatigue life
• 刊名：Materials Science & Engineering A
• 出版年：2016
• 出版时间：1 January 2016
• 年：2016
• 卷：649
• 期：Complete
• 页码：93-103
• 全文大小：4981 K

文摘

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_蔚  =0, −1, −∞$-\mathrm{\infty }$). With a strain ratio of R_蔚$R_{\text{蔚}}$=−∞$-\mathrm{\infty }$, 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_蔚=0$R_{蔚}=0$ 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_蔚=0$R_{蔚}=0$ and R_蔚=-1$R_{蔚}=-1$, stronger cyclic hardening is exhibited at all the investigated strain amplitudes for R_蔚$R_{\text{蔚}}$=−∞$-\mathrm{\infty }$. 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_蔚$R_{\text{蔚}}$=−∞$-\mathrm{\infty }$, −1 and f45703fc24d" title="Click to view the MathML source">0$0$. The fatigue life with R_蔚$R_{\text{蔚}}$=−∞$-\mathrm{\infty }$ shows the highest and that with $R_{\mathrm{蔚}}=0$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.