# An Investigation on the Softening Mechanism of 5754 Aluminum Alloy during Multistage Hot Deformation

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

^{−1}and 1 s

^{−1}. To investigate the metadynamic recrystallization behavior, a range of inter-pass delay times (5–60 s) was employed. These tests simulated flat rolling to investigate how softening behaviors respond to controlled parameters, such as deformation temperature, strain rate, and delay times. These data allowed the parameters for the hot rolling process to be optimized. The dynamic softening at each pass and the effect of metadynamic recrystallization on flow properties and microstructural evolution were analyzed in detail. An offset yield strength of 0.2% was employed to calculate the softening fraction undergoing metadynamic recrystallization. A kinetic model was developed to describe the metadynamic recrystallization behaviors of the hot-deformed 5754 aluminum alloy. Furthermore, the time constant for 50% recrystallization was expressed as functions related to the temperature and the strain rate. The experimental and calculated results were found to be in close agreement, which verified the developed model.

## 1. Introduction

## 2. Materials and Material Testing

#### 2.1. Materials

#### 2.2. Material Testing

^{−1}and 1 s

^{−1}) were used. The deformation degree is the same in the two deformation passes, and a height reduction of 35% was adopted at each stage. The specimens would be held for times ranging from 5 s to 60 s at the deformation temperature during the inter-pass periods. In order to calculate the softening fraction, a second deformation pass was acquired.

## 3. Results and Discussion

#### 3.1. Dynamic Softening Behavior

^{−1}, showing the dynamic softening behavior after peak stress. Generally, the yield stress at the second deformation stage decreases with an increasing delay time under the same temperature and the same strain rate. Verlinden et al. [21,22] proposed relative softening (RS) to quantify dynamic softening. The equation can be expressed as

_{p}is the value of peak stress and σ

_{p+0.25}is the value taken at a strain of 0.25 beyond the peak (Figure 5). Dynamic hardening occurs as RS < 0, and dynamic softening occurs as RS > 0. The measured RS values (4.6%, 2.0%, 6.9%, and 5.2%) indicate that dynamic softening occurred here. The obtained stress–strain curves under all test conditions are single-peak without oscillation, which is an indication of softening behavior due to continuous dynamic recrystallization (CDRX) [23,24]. Furthermore, the RS values at the second deformation stage are smaller than those at the first. The inhomogeneous deformation and friction at high strain (ε > 0.6) lead to smaller RS values and to little dependence on delay times during inter-pass periods at the same temperature and the same strain rate. Those results signify that a dynamic softening fraction may approach zero with further straining at the second deformation stage.

#### 3.2. Modeling the Kinetics of Metadynamic Recrystallization

_{1}and σ

_{2}are the offset stresses at the first and second deformation stage, respectively, and σ

_{m}is the flow stress at the interval (Figure 5).

_{0.5}is an empirical time constant for 50% recrystallization, which can be widely expressed as

_{m}is the activation energy for recrystalliation. $\dot{\mathsf{\epsilon}}$ and T are the strain rate and the deformation temperature, respectively.

#### 3.2.1. Determination of n

#### 3.2.2. Determination of the Dependence of t_{0.5} on Deformation Parameters

_{0.5}and strain rate $\dot{\mathsf{\epsilon}}$ into the above equation. Material constant m and activation energy for metadynamic recrystallization Q can be obtained via linear fitting. Figure 9 shows a relationship between lnt

_{0.5}and ln$\dot{\mathsf{\epsilon}}$, as well as lnt

_{0.5}and 1/T. The activation energy for metadynamic recrystallization Q is 18.045 KJ/mol. Much previous investigation has been focused on softening mechanisms during the inter-pass period of different aluminum alloys [2,29,30]. The exponent n and the present study is lower than that obtained for Al-5Mg and Al-9Mg alloy, i.e., n = 3.6 [30]. The variation of Avrami exponent n and activation energy Q values may be found for several reasons such as a decreasing growth rate or due to more planar growth morphology. In addition, the content of Mg will also lead to different activation energy for recrystallization.

#### 3.3. Verification of the Developed Kinetic Equation

_{i}and P

_{i}are the measured and calculated softening fraction, respectively. $\overline{E}$ and $\overline{P}$ are the average values of E

_{i}and P

_{i}, and N is the total number of the tested samples. The correlation coefficient is a reflection of the linear relationship between the experimental and predicted data. The AARE is an unbiased statistical parameter used to evaluate the predictability of a model that can be calculated through a term-by-term comparison of relative error [31,32].

## 4. Conclusions

- (1)
- The relative softening values under different test conditions signify the occurrence of dynamic softening at each stage, and the softening fraction may approach zero with further straining at the second deformation stage.
- (2)
- For the two-pass hot compressed 5754 aluminum alloy, the restoration mechanism is governed by metadynamic recrystallization. The softening fraction attributed to metadynamic recrystallization increases with increasing deformation temperature, delay time, and strain rate.
- (3)
- The predicted results were highly consistent with the experimental ones, which indicates that the developed kinetics equation can accurately describe the metadynamic recrystallization behaviors of 5754 aluminum alloy.

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

- Sang, D.; Li, Y. The Hot Deformation Activation Energy of 7050 Aluminum Alloy under Three Different Deformation Modes. Metals
**2016**, 49, 1–8. [Google Scholar] [CrossRef] - Lin, Y.C.; Li, L.T.; Xia, Y.C. A new method to predict the metadynamic recrystallization behavior in 2124 aluminum alloy. Comput. Mater. Sci.
**2011**, 50, 2038–2043. [Google Scholar] [CrossRef] - Zhou, M.; Clode, M.P. Constitutive equations for modeling flow softening due to dynamic recovery and heat generation during plastic deformation. Mech. Mater.
**1988**, 27, 63–76. [Google Scholar] [CrossRef] - Zhang, H.; Yang, L.B.; Peng, D.S.; Meng, L.P. Flow stress equation for multipass hot-rolling of aluminum alloys. Cent. South Technol.
**2011**, 8, 13–17. [Google Scholar] [CrossRef] - Zhang, H.; Yang, L.B.; Peng, D.S.; Meng, L.P. Recrystallization model for hot-rolling of 5182 aluminum alloy. Trans. Nonferr. Met. Soc. China
**2011**, 11, 382–386. [Google Scholar] - Sang, H.C.; Kim, S.I.; Yoo, Y.C. Determination of ‘no-recrystallization’ temperature of Invar alloy by fractional softening measurement during the multistage deformation. Mater. Sci. Lett.
**1997**, 16, 1836–1837. [Google Scholar] - Zheng, B.; Lin, Y.; Zhou, Y.; Lavernia, E.J. Gas Atomization of Amorphous Aluminum Powder: Part II. Experimental Investigation. Metall. Mater. Trans. B
**2009**, 40, 995–1004. [Google Scholar] [CrossRef] - Ding, H.L.; Wang, T.Y.; Yang, L.; Kamado, S. FEM modeling of dynamical recrystallization during multi-pass hot rolling of AM50 alloy and experimental verification. Trans. Nonferr. Met. Soc. China
**2013**, 23, 2678–2685. [Google Scholar] [CrossRef] - Xiang, S.; Liu, D.Y.; Zhu, R.H.; Jin-Feng, L.I.; Chen, Y.L.; Zhang, X.H. Hot deformation behavior and microstructure evolution of 1460 Al–Li alloy. Trans. Nonferr. Met. Soc. China
**2015**, 25, 3855–3864. [Google Scholar] [CrossRef] - Lin, Y.C.; Chen, M.S.; Zhong, J. Study of metadynamic recrystallization behaviors in a low alloy steel. J. Mater. Process. Technol.
**2009**, 29, 2477–2482. [Google Scholar] [CrossRef] - Lin, Y.C.; Chen, M.S.; Zhong, J. Study of static recrystallization kinetics in a low alloy steel. Comput. Mater. Sci.
**2008**, 44, 316–321. [Google Scholar] [CrossRef] - Shi, C.; Lai, J.; Chen, X.G. Microstructural Evolution and Dynamic Softening Mechanisms of Al-Zn-Mg-Cu Alloy during Hot Compressive Deformation. Materials
**2014**, 7, 244–264. [Google Scholar] [CrossRef] - Liu, Y.; Shao, Y.; Liu, C.; Chen, Y.; Zhang, D. Microstructure Evolution of HSLA Pipeline Steels after Hot Uniaxial Compression Microstructure Evolution of HSLA Pipeline Steels after Hot Uniaxial Compression. Materials
**2016**, 9, 721. [Google Scholar] [CrossRef] - Jiang, F.; Zhang, H.; Li, L.; Chen, J. The kinetics of dynamic and static softening during multistage hot deformation of 7150 aluminum alloy. Mater. Sci. Eng. A Struct.
**2012**, 552, 269–275. [Google Scholar] [CrossRef] - Maghsoudi, M.H.; Zarei-Hanzaki, A.; Changizian, P.; Marandi, A. Metadynamic recrystallization behavior of AZ61 magnesium alloy. Mater. Des.
**2014**, 57, 487–493. [Google Scholar] [CrossRef] - Zhang, P.; Yi, C.; Chen, G.; Qin, H.; Wang, C. Constitutive model based on dynamic recrystallization behavior during thermal deformation of a nickel-based superalloy. Metals
**2016**, 6, 1–19. [Google Scholar] [CrossRef] - Sun, Z.C.; Liu, L.; Yang, H. Microstructure evolution of different loading zones during TA15 alloy multi-cycle isothermal local forging. Mater. Sci. Eng. A Struct.
**2011**, 528, 5112–5121. [Google Scholar] [CrossRef] - Mandal, S.; Bhaduri, A.K.; Sarma, V.S. A study on microstructural evolution and dynamic recrystallization during isothermal deformation of a Ti-modified austenitic stainless steel. Metall. Mater. Trans. A
**2011**, 42, 1062–1072. [Google Scholar] [CrossRef] - Zhang, D.X.; Yang, X.Y.; Sun, H.; Li, Y.; Wang, J.; Zhang, Z.R.; Ye, Y.X.; Sakai, T. Dynamic recrystallization behaviors and the resultant mechanical properties of a Mg-Y-Nd-Zr alloy during hot compression after aging. Mater. Sci. Eng. A Struct.
**2015**, 640, 51–60. [Google Scholar] [CrossRef] - Agnoli, A.; Bernacki, M.; Logé, R.; Franchet, J.M.; Laigo, J.; Bozzolo, N. Selective Growth of Low Stored Energy Grains During δ Sub-solvus Annealing in the Inconel 718 Nickel-Based Superalloy. Met. Mater. Trans. A
**2015**, 46, 4405–4421. [Google Scholar] [CrossRef] - Verlinden, B.; Wouters, P.; McQueen, H.J.; Aernoudt, E.; Delaey, L.; Cauwenberg, S. Effect of homogenization and precipitation treatments on the hot workability of aluminum alloy AA2024. Mater. Sci. Eng. A Struct.
**1900**, 123, 239–245. [Google Scholar] - Verlinden, B.; Wouters, P.; McQueen, H.J.; Aernoudt, E.; Delaey, L.; Cauwenberg, S. Effect of different homogenization treatments on the hot workability of aluminum alloy AA2024. Mater. Sci. Eng. A Struct.
**1900**, 123, 229–237. [Google Scholar] [CrossRef] - Haghdadi, N.; Cizek, P.; Beladi, H.; Hodgson, P.D. A novel high-strain-rate ferrite dynamic softening mechanism facilitated by the interphase in the austenite/ferrite microstructure. Acta Mater.
**2017**, 126, 44–57. [Google Scholar] [CrossRef] - Liu, C.M.; Jiang, S.N.; Zhang, X.M. Continuous dynamic recrystallization and discontinuous dynamic recrystallization in 99.99% polycrystalline aluminum during hot compression. Trans. Nonferr. Met. Soc. China
**2005**, 15, 82–86. [Google Scholar] - Zhang, H.; Lin, G.Y.; Peng, D.S.; Yang, L.B.; Lin, Q.Q. Dynamic and static softening behaviors of aluminum alloys during multistage hot deformation. J. Mater. Process. Technol.
**2004**, 148, 245–249. [Google Scholar] [CrossRef] - Jung, K.H.; Lee, H.W.; Im, Y.T. A microstructure evolution model for numerical prediction of austenite grain size distribution. Int. J. Mech. Sci.
**2010**, 52, 1136–1144. [Google Scholar] [CrossRef] - Yue, C.X.; Zhang, L.W.; Liao, S.L.; Gao, H.J. Mathematical models for predicting the austenite grain size in hot working of GCr15 steel. Comput. Mater. Sci.
**2009**, 45, 462–466. [Google Scholar] [CrossRef] - Toloui, M.; Serajzadeh, S. Modelling recrystallization kinetics during hot rolling of AA5083. J. Mater. Process. Technol.
**2007**, 184, 345–353. [Google Scholar] [CrossRef] - Raghunathan, N.; Zaidi, M.A.; Sheppard, T. Recrystallization kinetics of Al-Mg alloys AA 5056 and AA 5083 after hot deformation. Mater. Sci. Technol.
**1986**, 9, 938–945. [Google Scholar] [CrossRef] - McQueen, H.J.; Ryum, N. Hot working and subsequent static recrystallization of Al and Al-Mg alloys. Scand. J. Metall.
**1985**, 14, 183–194. [Google Scholar] - Haghdadi, N.; Martin, D.; Hodgson, P. Physically-based constitutive modelling of hot deformation behavior in a LDX 2101 duplex stainless steel. Mater. Des.
**2016**, 106, 420–427. [Google Scholar] [CrossRef] - Haghdadi, N.; Zarei-Hanzaki, A.; Abedi, H.R. The flow behavior modeling of cast A356 aluminum alloy at elevated temperatures considering the effect of strain. Mater. Sci. Eng. A Struct.
**2012**, 535, 252–257. [Google Scholar] [CrossRef]

**Figure 4.**Typical true stress–strain curves of two-pass hot deformation under (

**a**) delay time of 5 s; (

**b**) delay time of 30 s; (

**c**) delay time of 60 s; (

**d**) temperature 450 °C and strain rate 0.1 s

^{−1}.

**Figure 6.**The optical microstructures after two-pass hot deformation for various inter-pass delay time of (

**a**) 5 s, (

**b**) 30 s, and (

**c**) 60 s.

**Figure 9.**Relationship between (

**a**) lnt

_{0.5}and ln$\dot{\mathsf{\epsilon}}$; (

**b**) lnt

_{0.5}and 1/T.

**Figure 10.**The comparison of the experimental and the calculated metadynamic softening fraction at different deformation temperatures.

Composition | Si | Cu | Mg | Zn | Mn | Gr | Al |

Content (wt %) | 0.40 | 0.10 | 2.6~3.6 | 0.20 | 0.50 | 0.30 | Bal |

© 2017 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

Huang, C.-Q.; Deng, J.; Wang, S.-X.; Liu, L.-l.
An Investigation on the Softening Mechanism of 5754 Aluminum Alloy during Multistage Hot Deformation. *Metals* **2017**, *7*, 107.
https://doi.org/10.3390/met7040107

**AMA Style**

Huang C-Q, Deng J, Wang S-X, Liu L-l.
An Investigation on the Softening Mechanism of 5754 Aluminum Alloy during Multistage Hot Deformation. *Metals*. 2017; 7(4):107.
https://doi.org/10.3390/met7040107

**Chicago/Turabian Style**

Huang, Chang-Qing, Jie Deng, Si-Xu Wang, and Lei-lei Liu.
2017. "An Investigation on the Softening Mechanism of 5754 Aluminum Alloy during Multistage Hot Deformation" *Metals* 7, no. 4: 107.
https://doi.org/10.3390/met7040107