Strain hardening of as-extruded Mg-xZn (x = 1, 2, 3 and 4 wt%) alloys

doi:10.1016/j.jmst.2018.09.015

Abstract

Abstract:

The influence of Zn on the strain hardening of as-extruded Mg-xZn (x?=?1, 2, 3 and 4?wt%) magnesium alloys was investigated using uniaxial tensile tests at 10^-3 s^-1 at room temperature. The strain hardening rate, the strain hardening exponent and the hardening capacity were obtained from true plastic stress-strain curves. There were almost no second phases in the as-extruded Mg-Zn magnesium alloys. Average grain sizes of the four as-extruded alloys were about 17.8?μm. With increasing Zn content from 1 to 4?wt%, the strain hardening rate increased from 2850?MPa to 6810?MPa at (σ-σ_0.2)?=?60?MPa, the strain hardening exponent n increased from 0.160 to 0.203, and the hardening capacity, Hc increased from 1.17 to 2.34. The difference in strain hardening response of these Mg-Zn alloys might be mainly caused by weaker basal texture and more solute atoms in the α-Mg matrix with higher Zn content.

Key words: Mg-Zn alloy, Strain hardening, Dislocation, Basal texture

Chaoyue Zhao, Xianhua Chen, Fusheng Pan, Jingfeng Wang, Shangyu Gao, Teng Tu, Chunquan Liu, Jiahao Yao, Andrej Atrens. Strain hardening of as-extruded Mg-xZn (x = 1, 2, 3 and 4 wt%) alloys[J]. J. Mater. Sci. Technol., 2019, 35(1): 142-150.

Figures/Tables 13

Table 1 Chemical compositions of the Mg-Zn alloys (wt%).

Alloy	Mg-1Zn	Mg-2Zn	Mg-3Zn	Mg-4Zn
Design composition	1	2	3	4
Actual composition	1.00	2.16	3.13	3.99

Fig. 1. XRD patterns of as-extruded Mg-Zn alloys.

Fig. 2. Optical micrographs of asextruded Mg-Zn alloys：(a) Mg-1Zn, (b) Mg-2Zn, (c) Mg-3Zn, (d) Mg-4Zn.

Fig. 3. EDS maps of as-extruded Mg-Zn samples: (a, b) Mg-1Zn, (c, d) Mg-4Zn.

Fig. 4. IPF maps and average grain size of as-extruded Mg-Zn alloys: (a) Mg-1Zn, (b) Mg-2Zn, (c) Mg-3Zn, (d) Mg-4Zn, (e) legend of IPF map, (f) average grain size.

Fig. 5. (a) Pole ?gures of as-extruded Mg-Zn alloys, (b) variation of intensity of basal texture with different Zn content.

Fig. 6. EBSD maps of as-extruded Mg-Zn samples after tensile fracture: IPF maps of Mg-1Zn (a), Mg-2Zn (c), Mg-3Zn (e) and Mg-4Zn (g); band contrast maps of Mg-1Zn (b), Mg-2Zn (d), Mg-3Zn (f) and Mg-4Zn (h).

Fig. 7. TEM images of as-extruded Mg-Zn alloys: (a) Mg-1Zn, (b) Mg-4Zn.

Fig. 8. Engineering (a) and true (b) stress-strain curves for as-extruded samples.

Table 2 Yield strength (σ0.2), ultimate tensile strength (σUTS), elongation-to-failure (εf), uniform strain (εp), hardening capacity (Hc) and strain hardening exponent (n) of the as-extruded Mg-Zn specimens.

Alloy	σ_UTS (MPa)	σ_0.2 (MPa)	ε_f (%)	ε_p (%)	Hc	n
Mg-1Zn	254	116	16.2	14.9	1.17	0.160
Mg-2Zn	258	109	16.4	15.2	1.36	0.164
Mg-3Zn	276	98	18.5	17.0	1.81	0.183
Mg-4Zn	297	89	20.6	19.1	2.34	0.203

Fig. 9. Strain-hardening curves for as-extruded samples: (a) θ-(σ-σ0.2), (b) θ-εp.

Fig. 10. Relationship between (σ-σ0.2)θ and (σ-σ0.2) for as-extruded Mg-Zn alloys.

Table 3 Parameters for dislocation slip systems of the as-extruded Mg-Zn alloys.

Alloy	Basal <a>		Prism <a>		<c+a> Second order		τ_prism/τ_basal	τ_<_c₊_a_>/τ_basal
Alloy	m_s,b	τ_basal	m_s,p	τ_prism	m_<_c₊_a_>	τ_<_c₊_a_>	τ_prism/τ_basal	τ_<_c₊_a_>/τ_basal
Mg-1Zn	0.16	18.5	0.45	76.5	0.43	73.1	4.1	3.9
Mg-2Zn	0.17	18.5	0.44	74.8	0.42	70.1	4.0	3.8
Mg-3Zn	0.19	18.6	0.44	72.1	0.41	67.2	3.9	3.6
Mg-4Zn	0.21	18.7	0.43	69.6	0.39	63.2	3.7	3.4

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