Effects of icosahedral phase on mechanical anisotropy of as-extruded Mg-14Li (in wt%) based alloys

doi:10.1016/j.jmst.2019.07.028

Abstract

Abstract:

Through investigating and comparing microstructure and crystallographic texture of as-extruded Mg-14Li and Mg-14Li-6Zn-1Y (in wt%) alloys, the differences in their mechanical anisotropy were investigated. It revealed that the formation of I-phase (Mg₃Zn₆Y, icosahedral structure) can effectively refine grain size. Moreover, compared with Mg-14Li alloy, the texture type of Mg-14Li-6Zn-1Y alloy changed slightly, but its texture intensity decreased remarkably. As a result, the stronger texture contributed to the “normal” mechanical anisotropy of Mg-14Li alloy with higher tensile strength and a lower elongation ratio along transverse direction (TD) than those along extrusion direction (ED). However, for Mg-14Li-6Zn-1Y alloy, the zonal distribution of I-phase particles along ED caused “abnormal” mechanical anisotropy, i.e. higher tensile strength and better plasticity along ED.

Key words: Mg-Li alloys, Texture, I-phase, Mechanical anisotropy, Fracture

Chuanqiang Li, Daokui Xu, Baojie Wang, Liyuan Sheng, Ruizhi Wu, Enhou Han. Effects of icosahedral phase on mechanical anisotropy of as-extruded Mg-14Li (in wt%) based alloys[J]. J. Mater. Sci. Technol., 2019, 35(11): 2477-2484.

Figures/Tables 8

Fig. 1. XRD patterns of as-extruded Mg-14Li and Mg-14Li-6Zn-1Y alloys.

Fig. 2. Backscattered electron (BSE) images of (a) Mg-14Li and (c) Mg-14Li-6Zn-1Y alloys; (b) and (d) the high-magnification observations to squared areas in images (a) and (c), respectively; (e) EDS of the white particles in (d); (f) TEM observation to I-phase and its typical 5-fold diffraction pattern inserted.

Fig. 3. Optical observations to the etched surface of (a) Mg-14Li and (b) Mg-14Li-6Zn-1Y alloys.

Fig. 4. Pole figures of (a) Mg-14Li and (b) Mg-14Li-6Zn-1Y alloys.

Fig. 5. Engineering tensile stress-strain curves tested along the “ED” and “TD” directions of (a) Mg-14Li and (b) Mg-14Li-6Zn-1Y alloys.

Table 1 Mechanical properties of as-extruded Mg-14Li and Mg-14Li-6Zn-1Y alloys with different orientations.

Alloys	Orientation	YS (MPa)	UTS (MPa)	EL (%)
Mg-14Li	ED	82 ± 3	111 ± 5	40.8 ± 2 .4
Mg-14Li	TD	106 ± 5	131 ± 3	19.5 ± 1.8
Mg-14Li-6Zn-1Y	ED	149 ± 4	168 ± 5	28.2 ± 2.1
Mg-14Li-6Zn-1Y	TD	137 ± 3	156 ± 5	13.5 ± 1.5

Fig. 6. Observations to fracture surfaces of (a) and (c) “ED” and “TD” samples of Mg-14Li alloy, (e) and (g) “ED” and “TD” samples of Mg-14Li-6Zn-1Y alloy, (b), (d), (f) and (h) the high-magnification observations to the squared areas in images (a), (c), (e) and (g), respectively.

Fig. 7. Observations to the side surfaces of (a) and (c) “ED” and “TD” samples of Mg-14Li alloy, (e) and (g) “ED” and “TD” samples of Mg-14Li-6Zn-1Y alloy. Images (b), (d), (f) and (h) the high-magnification observations to the squared areas in images (a), (c), (e) and (g), respectively.

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