Effects of samarium content on microstructure and mechanical properties of Mg-0.5Zn-0.5Zr alloy

doi:10.1016/j.jmst.2019.01.019

Abstract

Abstract:

Effects of samarium (Sm) content (0, 2.0, 3.5, 5.0, 6.5 wt%) on microstructure and mechanical properties of Mg-0.5Zn-0.5 Zr alloy under as-cast and as-extruded states were thoroughly investigated. Results indicate that grains of the as-cast alloys are gradually refined as Sm content increases. The dominant intermetallic phase changes from Mg₃Sm to Mg₄₁Sm₅ till Sm content exceeds 5.0 wt%. The dynamically precipitated intermetallic phase during hot-extrusion in all Sm-containing alloys is Mg₃Sm. The intermetallic particles induced by Sm addition could act as heterogeneous nucleation sites for dynamic recrystallization during hot extrusion. They promoted dynamic recrystallization via the particle stimulated nucleation mechanism, and resulted in weakening the basal texture in the as-extruded alloys. Sm addition can significantly enhance the strength of the as-extruded Mg-0.5Zn-0.5 Zr alloy at room temperature, with the optimal dosage of 3.5 wt%. The optimal yield strength (YS) and ultimate tensile strength (UTS) are 368 MPa and 383 MPa, which were enhanced by approximately 23.1% and 20.8% compared with the Sm-free alloy, respectively. Based on microstructural analysis, the dominant strengthening mechanisms are revealed to be grain boundary strengthening and dispersion strengthening.

Key words: Magnesium alloys, Samarium, Transmission electron microscopy (TEM), Microstructure, Mechanical properties

Kai Guan, Fanzhi Meng, Pengfei Qin, Qiang Yang, Dongdong Zhang, Baishun Li, Wei Sun, Shuhui Lv, Yuanding Huang, Norbert Hort, Jian Meng. Effects of samarium content on microstructure and mechanical properties of Mg-0.5Zn-0.5Zr alloy[J]. J. Mater. Sci. Technol., 2019, 35(7): 1368-1377.

Figures/Tables 12

Table 1 Chemical composition of the presented alloys (wt%).

Alloy	Sm	Zn	Zr	Mg	Fe	Si
A	-	0.57	0.45	Bal.	0.0014	0.0211
B	2.04	0.65	0.53	Bal.	0.0023	0.0173
C	3.33	0.55	0.46	Bal.	0.0015	0.0186
D	4.87	0.56	0.56	Bal.	0.0018	0.0053
E	6.31	0.54	0.51	Bal.	0.0019	0.0059

Fig. 1. OM micrographs of as-cast alloys of (a) alloy A, (b) alloy B, (c) alloy C, (d) alloy D, (e) alloy E and (f) average grain size.

Fig. 2. SEM micrographs of as-cast alloys of (a) alloy A, (b) alloy B, (c) alloy C, (d) alloy D, (e) alloy E and (f) volume frequency of intermetallic compounds.

Fig. 3. XRD patterns of as-cast samples.

Fig. 4. BF-TEM images (a, e, i, m), corresponding SAED patterns (b, c, f, g, j, k, n, o) and EDS spectra (d, h, l, p) of as-cast alloys of (a-d) alloy B, (e-h) alloy C, (i-l) alloy D and (m-p) alloy E.

Fig. 5. SEM micrographs of as-extruded alloys of (a) alloy A, (b) alloy B, (c) alloy C, (d) alloy D, (e) alloy E and (f) stringer width and particle size of stringers as a function of Sm content.

Fig. 6. HAADF-STEM images of as-extruded samples of (a) alloy A, (b) alloy B, (c) alloy C, (d) alloy D, (e) alloy E and (f) statistic grain diameter distributions in form of histogram for DRX grains.

Fig. 7. XRD patterns of as-extruded alloys.

Fig. 8. (a-c) BF-TEM images and (d-f) corresponding SAED patterns of as-extruded alloys of (a, d) alloy B, (b, e) alloy C, and (c, f) alloy D.

Fig. 9. (a) HAADF-STEM image of as-extruded alloy E, (b, c) corresponding SAED patterns and (d) EDS mappings along with (e, f) corresponding point EDS spectra.

Fig. 10. Relative intensities of peaks corresponding to basal (0002) plane of as-extruded samples.

Fig. 11. Tensile properties of as-extruded alloys.

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