Acta Metall Sin  2019, Vol. 55 Issue (12): 1512-1518    DOI: 10.11900/0412.1961.2019.00149
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Generation and Interaction Mechanism of Tension Kink Band in AZ31 Magnesium Alloy
ZHOU Bo1,2,SUI Manling1,2()
1. Institute of Microstructure and Properties of Advanced Materials, Beijing University of Technology, Beijing 100124, China
2. Beijing Key Laboratory of Microstructure and Properties of Solids, Beijing University of Technology, Beijing 100124, China
Abstract

The deformation structures, such as deformation twins, dislocations and kink bands, play an important role in the plasticity of magnesium alloys during the deformation process. However, due to the complexity of hcp structure, the deformation structures of the magnesium alloys, especially the interactions between deformation structures are still not well understood. Thus, it is of great scientific significance to study the microstructure of magnesium alloys, especially to characterize their structural characteristics of the interaction areas, which plays a significant role in understanding the structure and performance relationships of magnesium alloys. In this work, a combination of TEM and SAED pattern was applied to study the interaction mechanism associated with different kinds of deformation structures in Mg-Al-Zn (AZ31) alloy. When the applied external force is not beneficial for deformation twins and dislocations, kink bands act as a supplementary deformation mode to coordinate the asymmetry of hcp structure. According to crystallographic analysis, it is found that under the action of tensile stress nearly lie on basal plane in hcp structures, the basal dislocation pairs form and move to the opposite directions, forming tension kink band with the interface of {10$1ˉ$2} plane. The angle between the tension kink band interface and the basal plane is about 43°. The tension kink bands can further contribute to the strength and toughness of the material. These results will open a new insight into the understanding of interaction mechanism of deformation structures and greatly promote the development of Mg alloys.

Key words:  Mg alloy      kink band      deformation twins      TEM
 ZTFLH: TG146.22
Fund: National Natural Science Foundation of China(Nos.11374028);National Natural Science Foundation of China(U1330112);National Natural Science Foundation of China(51621003);Scientific Research Key Program of Beijing Municipal Commission of Education(No.KZ201310005002);Beijing Municipal Found for Scientific Innovation(No.PXM2019_014204_500031)
Corresponding Authors:  Manling SUI     E-mail:  mlsui@bjut.edu.cn
 Fig.1  Sample preparation methods(a) sample dimensions and rolling direction (RD, ND and TD are the rolling direction, normal direction and transverse direction of the sample, respectively)(b) schematic of the rolled sample prepared for TEM specimen Fig.2  TEM image of the high density kink bands (Two sets of approximately parallel kink bands: one group is K1, K3, K5, K7 and K9, while the other group is K2, K4 and K6) Fig.3  TEM analyses of the interaction of kink bands(a) TEM image of the interaction area (Subscript M indicates matrix)(b~e) SAED patterns of different areas in Fig.3a Fig.4  TEM analyses of interaction of {10$1ˉ$1}<10$1ˉ$$2ˉ$> twin and kink band(a) TEM image of the interaction area (The dashed blue lines and green lines indicate the kink band interface and the twin boundary, respectively; SFs—stacking faults)(b~e) SAED patterns of different areas in Fig.4a (Subscript T indicates twin) Fig.5  Schematics of the tension kink band formation mechanism(a) generation of dislocation pairs in initial structure (F indicate the force direction)(b) formation of K1 (α1 is the angle between the interface of K1 and the basal plane of matrix. The inset shows the orientation between the matrix and kink band under the external force)(c) interaction of K1 and K2 (α2 is the angle between the interface of K2 and the basal plane of matrix) Fig.6  Schematics of deformation structures(a) interaction between tension kink band and {10$1ˉ$1} twin (b) kink band (c) {10$1ˉ$1} twin Table 1  Schmid factors of different deformation structures