The hot flow behavior of Al-2wt.%Cu-1wt.%Mn alloy based on Gleebe-3800 hot compression simulation

Flow behavior of Al-2.0wt.%Cu-1.0wt.%Mn aluminum alloy was investigated by hot compressive test using a Gleebe-3800 thermal simulator. The test parameters about temperature and strain rate range from 573K to 773 K and from 0.01s to 5s, respectively, and the true strain is up to 0.6. It can be seen that the peak flow stress increases with increasing the strain rate and decreases by deformation temperature. And the deformation activation energy of Al-2.0wt.%Cu-1.0wt.%Mn alloy is 183.02KJ/mol. A constitutive equation has been constructed to predict the hot deformation behavior, and correlate the peak flow stress predicted with strain rate and deformation temperature. MATEC Web of Conferences 207, 03016 (2018) https://doi.org/10.1051/matecconf/201820703016 ICMMPM 2018 © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/).

by cryorolling followed by warm rolling can get a significant improvement in tensile strength (376MPa) and partial improvement in ductility (5%) as measured from tensile testing.
The peak flow stresses and the activation energy (Q) are measure indexes of difficulty for deformation.
Deng et.al [6] studied the flow behaviors of tension and compression considering the influence of deformation temperature and strain of 2024 aluminum alloy. Bardi et.al [7] investigates the correlation between the flow stresses and dynamic precipitation of 2618 aluminum alloy by means of torsion tests at temperatures between 423 and 573 K. Li et.al [8] used a Gleeble-1500 machine to investigate the flow stress features of 2519A aluminum alloy and to determine the optimum hot-working condition. Li et.al [9] studied the hot deformation behaviors of Ag-containing 2519 aluminum alloy by isothermal compression at 300 o C-500 o C with strain rates from 0.01s -1 to 10s -1 . Liu et.al [10] studied the flow behavior of Al-Cu-Mg-Ag alloy and obtained the value of hot deformation activation energy of the alloy. Few researchers study the hot flow behaviors of Al-Cu-Mn alloys with low Cu content, and relation of the precipitation phase T Mn to the flow behavior.
In this article, the hot deformation behavior of Al-2.0wt.%Cu-1.0wt.%Mn alloy is investigated at various temperatures and strain rates by Gleeble-3800 thermal simulator. The constitutive equation for the alloy is constructed relating flow stress, deformation temperature, strain rate, Zener-Hollomon parameter, and activation energy to deformation.

Experimental procedures
Al-2.0wt.%Cu-1.0wt.%Mn alloy was prepared in an electric resistance furnace using pure aluminum ingot and Al-20wt.%Cu and Al-10wt.%Mn master alloys. The chemical composition of the prepared alloy (Marked as A 1 alloy), measured by an MAX LMF15 spectrum, is listed in Table 1. After processing, the melts were poured into a metal mold with a size cavity size of 170mm20mm100mm (preheated at 250 o C for at least 5 hrs). Then small cylindrical specimens with 12 mm in height and 8 mm in diameter were cut from the castings, then solution-treated at 525 o C for 6 hrs +535 o C for 6hrs and terminated by a water quench.
A Gleebe-3800 thermal simulator is used to accomplish the isothermal compression test. In order to minimize friction and to make the specimen deform uniformly during the test, graphite foils were used as lubricant. Five temperatures (573, 623,673, 723 and 773 K) and four strain rates (10 -2 , 0.1, 1 and 5 s -1 ) were chosen as the experimental parameters. Specimens were heated to the test temperature at a heating rate of 5 K/s and held for 1.5 minutes. The specimens were compressed to a final strain of 0.6. The true strain-stress curves were recorded automatically. After deformation, the specimens were quenched immediately by water to preserve the as-deformed microstructure.   deformation temperatures (T) are shown in Fig.1 through hot compressive tests. The stress values corresponding to the deformation temperature at 573K(300 o C) and strain rate at 5s -1 are the highest, and the peak stress increases with increasing the strain rate for a given strain because there is not enough time to fully recrystallize in high strain rate, and decreases by deformation temperature due to the recovery or recrystallization. It is consistent with the results reported by Li et al. [11] and Ou et al. [12] .

Activation energy for deformation
It is usually accepted the flow behavior of material is controlled by thermal activation at elevated temperature, which is always described using Arrhenius type equation, in which a variable of activation energy is contained that stands for the difficulty for deformation.

RT
in which R is the universal gas constant (8.314 J mol -1 K -1 ), T is the absolute temperature (K), Q is the activation energy of hot deformation(kJ.mol -1 ).
Moreover, A 1 , A2, A, α, β, n 1 , n are material constants, Liu et al. [13] reported that dynamic recrystallization is generally favored at low Z values, which corresponds to low strain rates and high deformation temperatures.
Then the relationship between lnZ and ln[sinh(ασ)] is shown in Fig.4. So we can derive the values of lnB and n are 30.03 and 6.65 for A 1 alloy, respectively.

Conclusions
Hot deformation behaviors of Al-2Cu-1Mn alloy were researched by isothermal compression using a Gleebe-3800 thermal simulator. The main results are summarized as follows: (1)The deformation activation energy for Al-2Cu-1Mn alloy is obtained as 183.02KJ/mol through hot compressive test using a Gleebe-3800 thermal simulator.
(2)The constitutive equation for A 1 alloy has been established relating flow stress to deformation temperature and strain rate.
(3)It is easier to start dynamic recrystallization at higher temperature with strain rate 1s -1 than other conditions.