Effect of Nd on microstructure and mechanical properties of as-extruded Mg-Y-Zr-Nd alloy

doi:10.1016/j.jmst.2017.04.011

Abstract

Abstract:

The microstructure and mechanical properties of Mg-Y-Zr-xNd alloys with 0-2.63 wt% Nd were investigated using optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and tensile testing test. Results indicated that more Mg₂₄Y₅ particles and Mg₁₄Nd₂Y (β) phases were dispersed in the matrix when Nd content increased from 0 wt% to 2.63 wt% in the extruded alloys. Consequently, the nucleation of dynamic recrystallization and the volume fraction of recrystallized grains were promoted obviously. The average grain size can be refined in the range of 4.6-1.3 μm after the addition of 2.63 wt% Nd. The tensile strength of extruded alloys increased with increasing Nd content, and elongation exhibited an opposite change tendency. The extruded alloy sheet with 1.01 wt% Nd demonstrates optimal combination of strength and plasticity, i.e., the ultimate tensile strength, yield strength, and elongation were 273 MPa, 214 MPa, and 24.2%, respectively. Variations in mechanical properties are discussed on the basis of microstructure observations.

Key words: Mg-Y-Zr-Nd, Extrusion, Microstructure, Tensile properties, Precipitate

Xu Xiaoyang, Chen Xianhua, Du Weiwei, Geng Yuxiao, Pan Fusheng. Effect of Nd on microstructure and mechanical properties of as-extruded Mg-Y-Zr-Nd alloy[J]. J. Mater. Sci. Technol., 2017, 33(9): 926-934.

Figures/Tables 12

Table 1 Chemical compositions of as-cast Mg-Y-Zr-xNd alloys (wt%).

Alloy	Mg	Y	Nd	Zr	Fe	Si	Cu	Ni
YKN0	Bal.	4.95	0	0.53	0.0033	0.0086	0.0009	<0.0005
YKN0.5	Bal.	4.98	0.49	0.64	0.0038	0.0077	0.0013	<0.0005
YKN1	Bal.	5.08	1.01	0.74	0.0021	0.0073	0.0007	<0.0005
YKN3	Bal.	4.84	2.63	0.70	0.0025	0.0065	0.0006	<0.0005

Fig. 1. Optical micrographs of as-cast Mg-Y-Zr-xNd alloys: (a) YKN0; (b) YKN0.5; (c) YKN1; (d) YKN3.

Fig. 2. XRD patterns of as-extruded Mg-Y-Zr-xNd alloys: (a) YKN0; (b) YKN0.5; (c) YKN1; (d) YKN3.

Fig. 3. Optical micrographs of extruded Mg-Y-Zr-xNd alloys: (a) YKN0; (b) YKN0.5; (c) YKN1; (d) YKN3 (ED: extrusion direction; TD: transverse direction).

Fig. 4. Typical SEM micrographs showing the microstructures of extruded Mg-Y-Zr-xNd alloys: (a) YKN0; (b) YKN0.5; (c) YKN1; (d) YKN3.

Fig. 5. TEM images of extruded YKN1 alloy: (a) bright field image of precipitates; (b) a representative Mg24Y5 particle; (c) corresponding selected area electron diffraction (SAED) pattern.

Fig. 6. Macro-textures of extruded Mg-Y-Zr-xNd alloys: (a) YKN0; (b) YKN0.5; (c) YKN1; (d) YKN3.

Fig. 7. Typical tensile engineering stress-strain curves of extruded sheet samples: (a) YKN0; (b) YKN0.5; (c) YKN1; (d) YKN3.

Table 2 Tensile properties of as-extruded Mg-Y-Zr-xNd alloys at room temperature.

Alloy	UTS (MPa)	YS (MPa)	EL (%)
YKN0	231 ± 5	153 ± 2	29.1 ± 0.5
YKN0.5	256 ± 4	185 ± 3	27.4 ± 0.6
YKN1	273 ± 5	216 ± 4	24.2 ± 1.4
YKN3	285 ± 3	233 ± 2	4.7 ± 1.1

Fig. 8. SEM micrographs of fractured tensile samples of extruded alloys: (a) YKN0; (b) YKN0.5; (c) YKN1; (d) YKN3.

Table 3 Lattice parameters of magnesium and α-Mg of Mg-Y-Zr-xNd alloys.

Alloy	a (nm)	c (nm)	c/a
Mg	0.320890	0.521010	1.62364
YKN0	0.322076	0.521819	1.62017
YKN0.5	0.320369	0.519792	1.62247
YKN1	0.321685	0.521441	1.62096
YKN3	0.322134	0.521817	1.61987

Fig. 9. Optical microstructures of fracture surfaces for (a) YKN0 and (c) YKN3 and positions far away from the fracture surface for (b) YKN0 and (d) YKN3.

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