Flow Stress, Microstructural Evolution, and Constitutive Analysis During High-Temperature Deformation in Mg-4.4Li-2.5Zn-0.46Al-0.74Y Alloy

doi:10.11900/0412.1961.2020.00306

Acta Metall Sin

2021, Vol. 57

Issue (7): 860-870 DOI: 10.11900/0412.1961.2020.00306

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Flow Stress, Microstructural Evolution, and Constitutive Analysis During High-Temperature Deformation in Mg-4.4Li-2.5Zn-0.46Al-0.74Y Alloy

CAO Furong¹^,²^,³(

), DING Xin¹^,⁴, XIANG Chao¹, SHANG Huihui¹

^1.School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
^2.Key Laboratory of Lightweight Structural Materials Liaoning Province, Northeastern University, Shenyang 110819, China
^3.State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China
^4.Sichuan Aerospace Changzheng Equipment Manufacturing Co. , Ltd. , Chengdu 610000, China

Cite this article:

CAO Furong, DING Xin, XIANG Chao, SHANG Huihui. Flow Stress, Microstructural Evolution, and Constitutive Analysis During High-Temperature Deformation in Mg-4.4Li-2.5Zn-0.46Al-0.74Y Alloy. Acta Metall Sin, 2021, 57(7): 860-870.

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Abstract

Mg-Li alloys have potential applications in the aerospace, military, electronics, and automobile fields due to their superlight density, extremely high specific stiffness, high specific strength, damping, and electromagnetic shielding properties. Due to the limited slip systems of Mg and hcp-structured α(Mg) at room temperature, magnesium and α(Mg)-based alloys are difficult to deform; thus, it is significant to investigate the high-temperature deformation behavior to address this issue. Thus, in this study, an ultralight α(Mg)-based Mg-4.4Li-2.5Zn-0.46Al-0.74Y alloy was fabricated via multi-directional forging and rolling, and its flow stress, microstructural evolution, constitutive modeling, and deformation mechanism at elevated temperatures were investigated by tensile tests, OM, and XRD. The results indicate that the grain refinement mechanism of this alloy processed by multi-directional forging (MDF) exhibits mechanical shearing fragmentation and dynamic recrystallization (DRX). Additionally, the flow stress results demonstrate that strain-hardening occurred at 623 K due to grain coarsening, and microstructural evolution reveals that dynamic recovery and DRX occurred at tensile temperatures of 523-573 K; however, grain coarsening primarily appeared at 573 K (or more). XRD analysis demonstrates that this alloy comprised α(Mg), β(Li), Al₂Y, Al₁₂Mg₁₇, LiAl, and Mg₂Y phases, and hyperbolic sine constitutive analysis reveals that the stress exponent was 4.4 and the activation energy for deformation was 120.40 kJ/mol. The calculated results for dislocation density, number of dislocations in a grain, and atomic diffusion at 623 K and 1.67 × 10^-4 s^-1 corresponding to elongation-to-failure of 240% indicate that dislocation creep controlled by lattice diffusion governed the deformation mechanism under this condition. Predictions by grain growth models indicate that the calculated grain sizes were in good agreement with the practical grain sizes at 623 K and 1.67 × 10^-4 s^-1 when the grain growth factor was equal to 2 and proportional factor was 0.2.

Key words: Mg-Li alloy hot tension microstructure mechanical property constitutive analysis deformation mechanism

Received: 14 August 2020

ZTFLH:

TG146.2

Fund: National Natural Science Foundation of China(51334006)

About author: CAO Furong, researcher, Tel: 15998161852, E-mail: caofr@smm.neu.edu.cn

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	Furong CAO
	Xin DING
	Chao XIANG
	Huihui SHANG

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https://www.ams.org.cn/EN/10.11900/0412.1961.2020.00306 OR https://www.ams.org.cn/EN/Y2021/V57/I7/860

Fig.1 The true stress-true strain curves of Mg-4.4Li-2.5Zn-0.46Al-0.74Y (LZAY4301) alloy at different temperatures and strain rates of 1.67 × 10^-2 s^-1 (a), 1.67 × 10^-3 s^-1 (b), 5.0 × 10^-4 s^-1 (c), and 1.67 × 10^-4 s^-1 (d)

Fig.2 Microstructures of as-cast (a), MDF 1st pass (b), MDF 3rd pass (c), MDF 6th pass (d), cold-rolled along longitudinal direction (e), and annealed and held at 523 K for 1.25 h (f) in LZAY4301 alloy before high-temperature deformation (MDF—multi-directional forging, DRX—dynamic recrystallization)

Fig.3 XRD spectrum of LZAY4301 alloy annealed at 523 K for 1h

Fig.4 OM images of gauge section in LZAY4301 alloy after high-temperature deformation at temperatures of 523 K (a1-a4), 573 K (b1-b4), and 623 K (c1-c4), and strain rates of 1.67 × 10^-2 s^-1 (a1-c1), 1.67 × 10^-3 s^-1 (a2-c2), 5.00 × 10^-4 s^-1 (a3-c3), and 1.67 × 10^-4 s^-1 (a4-c4)

Table 1 The grains sizes and corresponding elongations of LZAY4301 alloy at different temperatures and strain rates

Fig.5 Curves of ln $ε ˙$ -lnσ (a), ln $ε ˙$ -σ (b), ln $ε ˙$ -ln[sinh(ασ)] (c), and ln[sinh(ασ)]-1 / T (d) of LZAY4301 alloys under high temperature tensile condition ( $ε ˙$ —strain rate, σ—true stress, α—stress multiplier factor, T—absolute temperature; the number adjacent to the regression line indicates specific slope)

Fig.6 Relation curve of lnZ-ln[sinh(ασ)] (a), and comparison of calculated stress and measured stress (b) (Z—Zener-Hollomon parameter, r²—related coefficient)

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