In this paper, deformation behaviors and microstructure evolution of a hot-rolled AZ31B magnesium alloy under cyclic loadings are investigated. The relationship between plastic deformation and microstructure evolution and the crack formation mechanisms are discussed. Under a high cyclic stress (90–140 MPa), steady ratcheting effect occurred in the material and the development of ratcheting strain went through three stages: 1) Stage I - initial rapid increase stage; 2) Stage II - steady stage; and 3) Stage III - final abrupt increase stage. Under a low cyclic stress (≤ 90 MPa), inconspicuous ratcheting effect was found in the material, indicating a light damage in the material. When the cyclic stress is below 30 MPa, no ratcheting effect is found and only elastic deformation occurs in the material. The formation of cracks in Stages I & II is mainly due to the activation of the basal slip system. The mean geometrically necessary dislocations (GND) are calculated to analyze the relationship between the basal slip and the ratcheting effect during the cyclic loading. Finally, a new approach is proposed to estimate the AZ31B magnesium alloy’s cyclic strength (at 107 cycles) according to the cyclic stress at which steady ratcheting effect starts to occur in the material.

Deformation behaviors and cyclic strength assessment of AZ31B magnesium alloy based on steady ratcheting effect

Disconnections and other defects associated with twin interfaces

Effect of local stress fields on twin characteristics in HCP metals

[Zhang, Z. J.; Zhang, P.; Li, L. L.; Zhang, Z. F.] Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China.;Zhang, ZF (reprint author), Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, 72 Wenhua Rd, Shenyang 110016, Peoples R China.;zhfzhang@imr.ac.cn

Fatigue cracking at twin boundaries: Effects of crystallographic orientation and stacking fault energy (vol 60, pg 3113, 2012)

A controversy concerning the description of twinning, whether it is shear-shuffle or pure glide-shuffle or pure shuffle, has developed. There is disagreement about the interpretation of transmission electron microscopic observations, atomistic simulations and theories for twin growth. In this article, we highlight the atomic-level, characteristic, equilibrium and non-equilibrium boundaries and corresponding boundary defects associated with the three-dimensional ‘normal’, ‘forward’ and ‘lateral’ propagation of growth/annealing and deformation twins. Although deformation twin boundaries (TBs) after recovery exhibit some similarity to growth/annealing TBs because of the plastic accommodation of stress fields, there are important distinctions among them. These distinctions distinguish among the mechanisms of twin growth and resolve the controversy. In addition, a new type of disconnection, a glide disclination, is described for twinning. Synchroshear, seldom considered, is shown to be a likely mechani...

https://tandfonline.com/doi/pdf/10.1080/21663831.2017.1336496

Interface structures and twinning mechanisms of twins in hexagonal metals

Interfacial structure of {101‾2} twin tip in deformed magnesium alloy

We performed transmission electron microscopy studies on dynamically deformed pure cobalt. The results show that the twinning plane of the most common twinning mode in hexagonal close-packed metals is non-coincident, that is, the twinning plane of the parent and the twin does not coincide. Statistical measurements show that only 44% of the twins have a misorientation angle close to the theoretical value of 86.3°, and 79% of the twin boundaries (TBs) deviate from the twinning plane. Thirty-two percent of the TBs deviate from the twinning plane by more than 40°. These results indicate that the twinning significantly departs from the classical twinning behavior.

https://www.tandfonline.com/doi/pdf/10.1080/21663831.2015.1034297

Non-classical Twinning Behavior in Dynamically Deformed Cobalt

Observations on the intersection between 101̅2 twin variants sharing the same zone axis in deformed magnesium alloy

https://par.nsf.gov/servlets/purl/10059819

Q. Sun

Papers

Interfacial structure of {101‾2} twin tip in deformed magnesium alloy

Non-classical Twinning Behavior in Dynamically Deformed Cobalt

Observations on the intersection between 101̅2 twin variants sharing the same zone axis in deformed magnesium alloy

Non-dislocation-mediated basal stacking faults inside 101−1 twins

Structural characterization of {101¯3} twin boundaries in deformed cobalt