Constitutive Relationship and Hot Processing Maps of Mg-Gd-Y-Nb-Zr Alloy

doi:10.1016/j.jmst.2015.10.019

Abstract

Abstract:

The hot working behavior of Mg-Gd-Y-Nb-Zr alloy was investigated using constitutive model and hot processing maps in this work. Isothermal compression tests were conducted with temperature and strain rate range of 703-773 K and 0.01-5 s^-1, respectively. Improved Arrhenius-type equation incorporated with strain compensations was used to predict flow behavior of the alloy, and the predictability was evaluated using correlation coefficient, root mean square error and absolute relative error. Processing maps were constructed at different strains for Mg-Gd-Y-Nb-Zr alloy based on dynamic materials model. The processing maps are divided into three domains and the corresponding microstructure evolutions are referred to the forming of straight grain boundaries, twinning, dynamic recrystallization and grain growth. Instability occurred mainly at the strain rate range of 0.3s^-1-0.5s^-1. The optimum processing domain is mainly at the temperature range of 703-765 K with the strain rate range of 0.01-0.1 s^-1.

Key words: Magnesium alloy, Recrystallization, Constitutive model, Processing maps, Hot deformation

Zhou Zhaohui, Fan Qichao, Xia Zhihui, Hao Aiguo, Yang Wenhua, Ji Wei, Cao Haiqiao. Constitutive Relationship and Hot Processing Maps of Mg-Gd-Y-Nb-Zr Alloy[J]. J. Mater. Sci. Technol., 2017, 33(7): 637-644.

Figures/Tables 10

Fig. 1. True stress-strain curves of Mg-Gd-Y-Nb-Zr alloy during hot compression: (a) ??=0.01s-1; (b) ??=0.1s-1; (c) ??=1s-1; (d) ??=5s-1.

Fig. 2. Microstructure of Mg-Gd-Y-Nb-Zr alloy deformed at various temperatures with strain rate of 0.1 s-1: (a) 703 K; (b) 743 K; (c) 773 K.

Fig. 3. Microstructure of Mg-Gd-Y-Nb-Zr alloy deformed at 743 K with different strain rate: (a) 5 s-1; (b) 1 s-1; (c) 0.01 s-1.

Fig. 4. Relationships between strain rate and flow stress: (a) ln??-ln σ; (b) ln??-σ; (c) ln??.

Fig. 5. Relationships between flow stress and temperature: (a) ln σ-1/T; (b) σ-1/T; (c) ln[sinh(ασ)]-1/T.

Fig. 6. Relationships between Z parameter and flow stress: (a) ln(Z)-ln σ; (b) ln(Z)-σ; (c) ln(Z).

Fig. 7. Relationships between constitutive constants and true strain of Mg-Gd-Y-Nb-Zr alloy: (a) α-?; (b) n-?; (c) ln A-?; (d) Q-?.

Table 1 Coefficients of polynomial of Mg-Gd-Y-Nb-Zr alloy

α	n	ln A	Q
B₀ = 0.01581	C₀ = 3.35810	D₀ = 35.85461	E₀ = 239266.16175
B₁ = -0.03341	C₁ = -5.40440	D₁ = -117.45446	E₁ = -792353.91592
B₂ = 0.17264	C₂ = 24.66499	D₂ = 488.19002	E₂ = 3277770
B₃ = -0.26886	C₃ = -40.84634	D₃ = -877.98264	E₃ = -5857970
B₄ = 0.16542	C₄ = 26.43542	D₄ = 564.89375	E₄ = 3762290

Fig. 8. Correlation between experimental and predicted flow stress data of Mg-Gd-Y-Nb-Zr alloy at the strain of 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6.

Fig. 9. Processing maps for Mg-Gd-Y-Nb-Zr alloy generated at strains of: (a) 0.1; (b) 0.2; (c) 0.3; (d) 0.4; (e) 0.5; (f) 0.6. The numbers represent percent efficiency of power dissipation and shaded areas correspond to instability regions. The processing maps are divided into three domains by red lines: domain I, domain II and domain III, meanwhile, the instability regions are defined as region 1 and region 2.

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