Y. HU et al.: DEFORMATION BEHAVIOR OF THE Mg-7Zn-3Cu-1Ce ALLOY DURING HOT COMPRESSION
215–223
DEFORMATION BEHAVIOR OF THE Mg-7Zn-3Cu-1Ce ALLOY
DURING HOT COMPRESSION
[TUDIJ DEFORMACIJE MAGNEZIJEVE ZLITINE Mg-7Zn-3Cu-1Ce
MED VRO^IM STISKANJEM
Yaobo Hu1, Wanqiu Meng1, Tianxu Zheng1, Chao Zhang1, Qin Yang2, Zhentao Zhu2
1Chongqing University, College of Materials Science and Engineering, 400044 Chongqing, China
2Chongqing Chang’an Global R&D Center, Chang’an Automobile Co, Ltd, 400044 Chongqing, China
yaobohu@cqu.edu.cn
Prejem rokopisa – received: 2017-07-25; sprejem za objavo – accepted for publication: 2017-10-02
doi:10.17222/mit.2017.124
The flow stress behavior of the Mg-7Zn-3Cu-1Ce alloy was studied on a Gleeble-1500 thermal/mechanical simulation test
machine under the maximum deformation degree of 50 %, at a strain rate of 0.01 s–1 to 10 s–1, and temperature of 573 to 673 K.
The hot deformation behavior of the tested alloy during the hot compression process was studied. The experimental results
showed that the correlation of the flow stress, strain rate and temperature was obvious and the tested alloy was a strain-rate-
sensitive material. The deformation activation energy (Q = 191 kJ/mol) and the corresponding stress exponent (n = 5.68) were
evaluated by linear regression analysis during the hot deformation process. And the flow stress constitutive equation of the
Mg-7Zn-3Cu-1Ce alloy was built by introducing the Zener-Hollomon parameter. There was no recrystallization phenomenon in
the microstructure of the tested alloy after hot-compression, and dynamic recovery is the main softening mechanism during the
high-temperature deformation. The extruded alloy (extrusion at 673 K) shows excellent mechanical properties both at room and
at mid-high temperature.
Keywords: hot deformation, deformation activation energy, stress exponent, dynamic recovery
Avtorji ~lanka so {tudirali napetost te~enja magnezijeve zlitine Mg-7Zn-3Cu-1Ce s pomo~jo termomehanskega simulatorja
Gleeble-1500 do maksimalne stopnje deformacije 50 %, pri hitrostih deformacije od 0,01 s–1 do 10 s–1 in v temperaturnem
obmo~ju med 573 K in 673 K. [tudirali so potek deformacije preiskovane zlitine med vro~im stiskanjem. Eksperimentalni
rezultati ka`ejo, da je korelacija med napetostjo te~enja, hitrostjo deformacije in temperaturo o~itna in da je preiskovani material
zelo ob~utljiv na hitrost deformacije. Aktivacijska energija za deformacijo (Q =191 kJ/mol) in odgovarjajo~i napetostni ekspo-
nent (n = 5,68) sta bila ovrednotena s pomo~jo linearne regresijske analize med procesom vro~e deformacije. S pomo~jo uvedbe
Zener-Hollomonovega parametra so zgradili konstitutivno ena~bo za napetost te~enja magnezijeve zlitine Mg-7Zn-3Cu-1Ce.
Ugotovili so da ni pri{lo do rekristalizacije mikrostrukture preiskovane zlitine po vro~em stiskanju in da je glavni mehanizem
meh~anja med visoko temperaturno deformacijo dinami~na poprava. Zlitina ekstrudirana pri 673 K ima odli~ne mehanske
lastnosti tako pri sobni, kot srednje povi{anih temperaturah.
Klju~ne besede: deformacija v vro~em, aktivacijska energija za deformacijo, napetostni eksponent, dinami~na poprava
1 INTRODUCTION
Magnesium alloys: with the advantages of high
specific strength, high specific stiffness, good damping
and electromagnetic shielding performance, show broad
application prospects, and have become some of the
ideal materials in automotive, aviation and other areas.1
The Mg-Zn alloy is a typical kind of high-strength
wrought magnesium alloy, adding Cu to the binary
Mg-Zn alloy will raise the solution temperature, so that
more Zn and Cu elements can be soluted into the Mg
matrix at higher solution temperature, this will enhance
the solution strengthening as well as the aging strength-
ening.2–3 ZC63 and ZC62 are two typical Mg-Zn-Cu
alloys, with the mechanical performance of as-cast ZC63
after aging being better than the AZ91 alloy.4 The
toughness of the as-cast ZC62 alloy at 423 K is better
than that of the AS21 alloy. Moreover, the casting pro-
ducts of ZC62 have been successfully applied in the
field, including car engine, thruster and other situations
those need to resist high temperature (423 K).
The poor ductility of magnesium alloys has been
attributed to highly anisotropic dislocation slip behavior.
Magnesium alloys have a hexagonal close-packed (hcp)
crystal structure, which makes it more difficult to con-
duct plastic deformation at room temperature. However,
some non-basal slip planes begin to be activated and the
number of slip systems increases at elevated temperature,
thus the plasticity and deformation performance are
improved.5–10 For example, the research of A. Chapuis
and J. H. Driver11 have shown that tensile twinning and
basal slip are only slightly temperature-dependent, but
the critical resolved shear stresses (CRSSs) value of
other systems (compressive twinning, prismatic and
pyramidal II (c+a) slip) decrease substantially with in-
creasing temperature. Therefore, it is of great importance
to study the plastic deformation behavior and processing
parameters of magnesium alloys at elevated temperature.
In recent years, the studies of the hot compressive defor-
mation behaviors of magnesium alloys mainly concen-
trated on the Mg-Al-Zn, Mg-Zn-Zr and Mg-Gd
Materiali in tehnologije / Materials and technology 52 (2018) 2, 215–223 215
UDK 620.1:66.040:669.721.5 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 52(2)215(2018)
series.7–10,12–13 The evolution of the microstructure and
texture of the AZ90 alloy during hot compression was
studied by H. Ding et al.12 and X. L. Hou et al.14 inves-
tigated the microstructure evolution of Mg-8Gd-2Y-
1Nd-0.3Zn-0.6Zr alloy subjected to hot compression at
623 K and strain rate of 0.5 s–1. However, the reports
about hot compressive deformation behaviors on Mg-
Zn-Cu series magnesium alloys are limited. T. Zhang et
al.15 added a certain amount of Sn to ZC63 alloy, the
results showed that the addition of Sn significantly
improved the strength of the ZC63 magnesium alloy due
to grain refinement strengthening, solid solution
strengthening and precipitation strengthening. Adding a
rare-earth element could have a beneficial effect on Mg
alloys.13–14,16–23 The creep resistance of the ZC63
magnesium alloy increased with adding La,3 and the
Ce-rich RE-containing alloy exhibited a better creep
resistance than the La-rich RE-containing alloy,19 mainly
due to the formation of a grain boundary network of
thermally stable phases, which can effectively inhibit
grain-boundary migration and sliding during the creep
process.
In this study, we added the rare-earth element Ce to
the basic Mg-7Zn-3Cu alloy. Then the hot compression
deformation behavior and the microstructure of the alloy
under different deformation rates at high temperature
were studied. The study of the relations of some relevant
parameters, such as stress exponent n, deformation acti-
vation energy Q and temperature T are also included.
The research results not only provide guides to the hot
working processes of the alloy, but also offer some
necessary experimental data and references to the nume-
rical simulation research of the Mg-Zn-Cu alloy pro-
cessing.
2 EXPERIMENTAL PART
The Mg-7Zn-3Cu-1Ce (mass fraction) magnesium
alloy was prepared by die casting using high-purity
magnesium (>99.98 w/%) and zinc (>99.97 w/%), as
well as Mg-(30 w/%)Cu, Mg-(20 w/%)Ce and Mg-(4
w/%)Mn magnesium-based master alloys. The melt was
protected with 99 % of volume fractions of CO2 and 1 %
of volume fractions of SF6 as protective gas during the
process of melting. The actual composition of the pre-
pared magnesium alloy is shown in Table 1. After homo-
genizing annealing (heated at 673 K for 24 h), experi-
mental samples (10 mm × 12 mm) were prepared for
the hot compression experiment. The samples were
gummed with graphitic lubricant on both sides to reduce
the impact of friction, then hot compression experiments
were conducted using a Gleeble-1500 thermal/mecha-
nical simulation machine. The heating rate was 276 K/s,
then held for 3 min, and the temperature for deformation
was (573, 623 and 673) K at different deformation rate
of (0.01, 0.1, 1 and 10) s–1, respectively. Meanwhile, the
expected maximum deformation value was 50 %. The
correlative experimental parameter referenced some
previous studies.24–25 After the hot deformation, the
samples were quenched immediately with cold water.
In this study, the morphology of as-cast, homoge-
nizing annealing and hot compression were studied by
optical microscopy, and scanning electron microscopy
(TESCAN VEGA 3 LMH SEM, only for as-cast). The
etching solution was a mixture of 90 mL alcohol, 5 mL
acetic acid, 5 g picric acid and 10 mL distilled water. In
order to get the phase composition of the alloy, phase
analyses of the cast sample (10 mm × 10 mm × 10 mm)
was analysed by X-ray diffraction (XRD Rigaku
D/MAX-2500PC X) with Cu-K, the range of scan angle
was between 10° and 90°, the scan speed was 4°/min and
we used Jade 5.0 software for the data analysis.
The extrusion temperature for the alloy was 573 K,
the extrusion ratio was about 81 and the extrusion rate
was 2.0×10–3/s. The samples used for tensile tests at
ambient and high temperature were prepared based on
GB/T228-2002 and GB/T4338-1995, respectively. The
tensile test was conducted by a CMT-5105 electronic
universal testing machine at the rate of 2 mm/min, with
the temperature of (273, 323, 348 and 373) K.
Y. HU et al.: DEFORMATION BEHAVIOR OF THE Mg-7Zn-3Cu-1Ce ALLOY DURING HOT COMPRESSION
216 Materiali in tehnologije / Materials and technology 52 (2018) 2, 215–223
Figure 1: Metallographic images of Mg-7Zn-3Cu-1Ce alloys: a) as-cast, b) homogenized
Table 1: Actual composition of the alloy, in mass fractions (w/%)
Mg Zn Cu Ce Mn
Bal. 7.2 3.4 0.9 0.3
3 RESULTS
3.1 As-cast structure of the alloy
Figure 1 shows the microstructure of the
Mg-7Zn-3Cu-1Ce alloy. It is clear that the as-cast
structure shows typical dendrite shapes, consisting of
-Mg matrix and net-like black compounds distributed
along the interdendritic. Dendritic segregation is ob-
vious; there are many compounds between the dendrites.
According to the Mg-Zn binary eutectic phase diagram,
the content of Zn in this alloy exceeds the maximum
solid solubility of Zn in Mg matrix (6.2 %), -Mg and
Mg-Zn binary phase generate directly from the liquid
phase at about 621 K. The addition of Cu makes the
original Mg-Zn binary phase change into eutectic Mg
(Zn, Cu) compound. It is clear from the XRD spectrum
(Figure 2), there are mainly diffraction peaks of -Mg,
Mg (Zn, Cu) and Mg (Zn, Cu)2 phase. But there is an
obvious diffraction peak at 2
 = 25°, which is attributed
to the second phase containing Ce, and it was identified
as thermally stable Mg12RE and MgRE compounds.3,24
As presented in Figure 3, it is obvious that a grain-
boundary interphase network is formed because of the
Ce-rich RE addition. It was reported that the addition of
Ce can reduce the solid solubility of other elements in
the Mg matrix and increases the volume fraction of
secondary phase.19 After homogenization treatment, only
a small amount of compounds dissolve into the matrix,
indicating that the inter-dendritic compounds have good
thermal stability at elevated temperature.3,15
3.2 True stress-strain curves
The true stress-strain (-) curves of Mg-7Zn-
3Cu-Ce alloy at different temperature are shown in
Figure 4. According to the curves, the entire com-
pression process can be divided into four stages,26 work-
hardening stage, stable stage, softening stage and steady
stage. This is mainly a composite effect of work hard-
ening and thermally activated softening.26 In the initial
stage of the compression, elastic and plastic deformation
occur, the true stress curve s linearly. This is primarily
caused by a second-order pyramidal slip system (c + a)
dislocation motion. The strain increases as the com-
pression continues, but dynamic recovery (DRV) or
dynamic recrystallization (DRX) occurs, which soften
the alloy, so the stress rises slowly to a maximum and
then goes down. The stress and strain appear steady flow
characteristics when the softening of DRV or DRX and
work hardening get to balance in a certain strain value
(such as the strain increased to around 0.2 with 573 K
and (0.01, 0.1, 1, 10) s–1; to 0.05 s–1 with 623 K and
0.01 s–1, to 0.25 s–1 with 623 K and 0.1 s–1, to 0.3 s–1 with
623 K and 1 s–1, to 0.15 s–1 with 623 K and 10 s–1; to
0.03 s–1 with 673 K and 0.01 s–1, to 0.05 s–1 with 673 K
and 0.1 s–1, to 0.25 s–1 with 673 K and (1, 10) s–1), while
the flow stress is nearly unchanged latterly. Comparing
the true stress-strain (–) curves at different tempera-
tures, under the same strain rate, the strain value of the
alloy reaches the stress peak decreases as the tempera-
ture increases. At the same time, the flow stress de-
creases as the temperature increases, indicating DRV and
DRX could happen more easily at elevated temperature
and the softening degree increases.27–28 On the other
hand, with the temperature increasing, the thermal
activation energy increases, the kinetic energy of the
atomic activity increases, the interatomic interaction
force decreases, the diffusion speed of various point
defects increases, the dislocation movement resistance
decreases, and the deformation is more favorable. At the
same temperature, the true stress of material increases
with the increasing of strain rate, since per unit time of
plastic deformation decreases and the number of dislo-
cation increases dramatically with the increase of strain
rate. The response time for DRV and DRX softening
Y. HU et al.: DEFORMATION BEHAVIOR OF THE Mg-7Zn-3Cu-1Ce ALLOY DURING HOT COMPRESSION
Materiali in tehnologije / Materials and technology 52 (2018) 2, 215–223 217
Figure 3: SEM micrograph of as-cast Mg-7Zn-3Cu-1Ce
Figure 2: X-ray diffraction pattern of Mg-7Zn-3Cu-1Ce as-cast alloy
decreases simultaneously, and there is not enough time
for plastic deformation, the critical resolved shear stress
of the alloy increases, hence, leading to the flow stress
increase.10,29–30
No prominent steady-state flow phenomenon could
be seen after reaching the peak stress at the strain rate
10 s–1. In the late stage of compression, the true stress
decreases rapidly. At a larger strain rate, analysis
suggests that the speed of dislocation multiplication
accelerated then enhances the density of dislocation;
therefore the stress of the alloy increases with the
increase of the strain. The stress falls down slowly when
the strain gets to a certain value (such as the strain
increased to around 0.4 s–1 with 573 K and (0.1, 10) s–1,
to 0.45 s–1 with 573 K and 1 s–1; to 0.55 s–1 with 623 K
and 1 s–1, to 0.36 s–1 with 623 K and 10 s–1; to 0.42 s–1
with 673 K and 10 s–1), and the strain strengthening
offsets the effect of DRV or DRX by softening. This is
why DRV and DRX play an important role during hot
deformation of magnesium alloys.31 However, the flow
stress falls down quickly when the strain’s cumulant
exceeds 0.6. At this point, the strain rate is high enough
to crush or reorganize the microstructure of the material,
which makes the flow stress fall down sharply. There are
many primary interdendritic compounds in as-cast
structures. Those could be elongated due to the deforma-
tion of the matrix during the compression process. It is
noteworthy that the primary interdendritic compounds
are crushed when the compression reaches a certain
degree and a few dot-like second phase distribute within
the matrix, while secondary dendrites connects each
other (Figure 10).
3.3 Establishment of the constitutive equation
According to the analysis of the true stress-strain
curve, there are obvious interactions between the flow
stress, temperature and strain rate. It can be explained by
the terms of DRX and dislocation generation or motion
mechanism in polycrystalline metals.26 Understanding
the mathematical relationship between them, we can ma-
ster the rule how flow stress changes during high-tem-
perature plastic deformation.
Heat deformation is a thermal activation process. Its
main feature behaves as the strain rate under the control
of heat activation and obeys the Arrhenius rule:1
  exp = −⎛⎝
⎜ ⎞
⎠
⎟
0
Q
RT
(1)
where Q is the deformation activation energy, R (8.31
J/(mol·K)) is the molar gas constant, T is the defor-
mation temperature (K),  is the strain rate (s–1). During
the actual heat deformation, flow stress is extremely
sensitive to the applied stress, strain rate and tempe-
rature.10
Steady flow stress  and strain rate  have the relation
of exponent function under a low stress level:
 = A n1 1 (2)
where A1 and n1 are temperature-independent constants.
Steady flow stress  and strain rate  have the relation
of power function under a high stress level:
 exp  != A2 (3)
where A2 and  are temperature-independent constants.
After many researches on hot working data, Sellars
and Tegart proposed an Arrhenius equation containing
activation energy Q and temperature T:30,33
[ ] sinh exp  != −⎛⎝⎜
⎞
⎠
⎟A
Q
RT
n
(4)
where  is a constant of stress level,  = /n1, n is stress
exponent, Q is deformation activation energy, R
(8.31J/(mol·K)) is molar gas constant, T is absolute tem-
perature (K).
To obtain the value of , we must first have the
values of n1 and . Take the logarithm on both sides of
Equations (2) and (3), respectively:
Y. HU et al.: DEFORMATION BEHAVIOR OF THE Mg-7Zn-3Cu-1Ce ALLOY DURING HOT COMPRESSION
218 Materiali in tehnologije / Materials and technology 52 (2018) 2, 215–223
Figure 4: True stress-strain curves of Mg-7Zn-3Cu-1Ce alloy at diffe-
rent temperature: a) 573 K, b) 623 K, c) 673 K
ln  ln ln = +A n1 1 (5)
ln  ln = +A2 (6)
The curves of ln  ln − and ln  − (Figure 5) could
be obtained by performing linear regression using the
least-squares method. It is easy to figure out the value of
the slope (n1) of fitting line under low stress level at the
temperature 623 K and 673 K (n1 = 7.09). While the
 = 0.109 (the slope of fitting line under high stress level
at the temperature 573 K and 623 K), so we can calculate
the value  = 0.0154 mm2/N.
Take the logarithm on both sides of Equation (4), as
follows:
[ ]ln  ln ln sinh   !+ = +Q RT A n (7)
Partial Equation (7), we can get the expression of n
and Q:
[ ]n
T
=
∂
∂
ln 
ln sinh

 !
(8)
[ ]
[ ]
Q R
T
Rnb
T
= =
∂
∂
∂
∂
ln 
ln sinh
ln sinh
( / )


 !
 !

1
(9)
According to Equation (8), we can get the stress
exponent n (Figure 6) by plotting and fitting the data of
ln  and [ ]ln sinh ! , so the average of n is 5.68.
According to Equation (9) similarly, Figure 7 is the
curve of [ ]ln sinh ! – T–1 and b = 4.04. By calculation
we can get the activation energy (Q = 1.91×102 kJ/mol)
of Mg-7Zn-3Cu-1Ce.
Zener and Hollomon derived and proved the relation-
ship between the strain rate and temperature could be
described by the Z parameter:
[ ]Z Q
RT
A
n
= ⎛⎝
⎜ ⎞
⎠
⎟ = exp sinh  ! (10)
Plug the value of Q into the above Equation (10), and
the expression of Z is as follows:
Z =  exp (1.91×102 /RT).
Take logarithm on both sides of equation (10) and we
get ln Z = ln A + n ln [sin ()]. Figure 8 shows the
relationship between Z and flow stress of experimental
Y. HU et al.: DEFORMATION BEHAVIOR OF THE Mg-7Zn-3Cu-1Ce ALLOY DURING HOT COMPRESSION
Materiali in tehnologije / Materials and technology 52 (2018) 2, 215–223 219
Figure 7: Relationship between flow stress and temperature of
Mg-7Zn-3Cu-1Ce
Figure 5: Relationship between strain rate and peak stress of
Mg-7Zn-3Cu-1Ce alloy: a) ln  ln − , b) ln  −
Figure 6: Relationship between strain rate and flow stress for
Mg-7Zn-3Cu-1Ce alloy
alloy and the correlation coefficient is 0.962. It can be
seen that high temperature compression deformation
behaviour can be described using hyperbolic sine func-
tion, and A = 7.82×1013 s–1.
According to the definition of inverse function of
hyperbolic sine function, we obtain the relation between
 and Z from Equation (10):


=
⎛
⎝
⎜ ⎞
⎠
⎟ +
⎛
⎝
⎜ ⎞
⎠
⎟ +
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
⎧
⎨
⎪
⎩
⎪
⎫
⎬
⎪
⎭
⎪
1
1
1 2
1
Z
A
Z
A
n n
n
(11)
Plug the value of , n and A into the above Equation
(11), then we obtain the steady-state flow stress consti-
tutive equation for thermal deformation of the experi-
mental alloy.
Figure 9 shows the comparison between predicted
value and measured value, and the slope of the fitting
curve is 0.996. indicating the constitution equation has
high accuracy.
3.4 The microstructure evolution of Mg-7Zn-3Cu-1Ce
during hot simulation
Figure 10 provides the OM images perpendicular to
the compression direction of the studied alloy after hot
compression between 573 K and 673 K at a strain rate of
(0.01, 0.1, 1 and 10) s–1. It is obvious that dendritic struc-
tures are significantly elongated because the softening of
the matrix. When the temperature range is between
573 K and 623 K, the microstructure is inhomogeneous
and only part of the dendrite squeezed together as the
matrix softening, forming a thin layer deformation zone.
The deformation of the structure is relatively uniform at
elevated temperature and almost all the dendrites parti-
cipate in the coordinated deformation, and inter-dendritic
eutectic structure becomes coarse, while slender macro-
scopic deformation zone reduces. Generally, hot defor-
mation is the contradiction process of work hardening,
DRV and DRX. Nevertheless, recrystallization or twins
appear in the microstructure at high temperature in the
previous studies.9–10 However, the DRX does not appear
in the microstructure at low strain rates between the
deformation temperatures 573 K and 673 K. This
indicates that DRV is the main softening mechanism in
the early stage of hot deformation.30 The opposite sign
dislocations on the same slip plane attract each other,
come together then disappear under the effect of thermal
activation energy. While the opposite sign dislocations
on the different slip plane disappear by vacancy conden-
sation or vacancy escape, thus the density of dislocation
decreases. The DRV mechanism turns into polygoni-
zation because the change of dislocation density with
deformation temperature increases. During the process
of recovery, dislocation moves, rearranges and ranges
along the direction perpendicular to the slip plane,
forming dislocation wall and sub-boundary or subgrain.23
This kind of sub-boundary cannot move easily that
would not become the recrystallization core. Simul-
taneously, dislocation’s polygonization occurs to release
the stored energy. These can reduce the driver for sub-
sequent recrystallization process. These eutectic struc-
tures are good thermal stability that could stabilize the
sub-grain, preventing the grain boundary move effec-
tively and slow down the process of DRX. S. W. Xu et
al.25 studied the dynamic microstructure changes in
AZ91 alloy during hot compression, showing the
Mg17Al12 precipitates has an importance pinning effect
for grain boundary and was greatly influenced by
compression temperature. This suggests that the solute
atoms or precipitates could influence the dynamic
recrystallization. Consequently, the DRX temperature is
increased.
3.5 Mechanical properties of as-extruded Mg-7Zn-
3Cu-1Ce
According to the analysis above, there is obvious
work hardening in the early stage of the deformation at
Y. HU et al.: DEFORMATION BEHAVIOR OF THE Mg-7Zn-3Cu-1Ce ALLOY DURING HOT COMPRESSION
220 Materiali in tehnologije / Materials and technology 52 (2018) 2, 215–223
Figure 8: The relationship between Z and flow stress of experimental
alloy
Figure 9: Comparison between predicted value and measured value
the temperature between 573 K and 623 K. There is a
steady flow phenomenon in the early stage of the
deformation when the deformation is conducted at the
temperature of 673 K. And the deformed structure is
most homogeneous at 673 K. This indicates that dyna-
mic recovery is the main softening mechanism at high
temperature, which is favorable for the shaping of the
alloy. In the present study, a higher temperature is
generally utilized because a high deformation rate occurs
during the extrusion process.12,24,32–34 Therefore, the
extrusion temperature can be determined to be 673 K in
this study. The mechanical properties of as-extruded
alloys at room and elevated temperature are summarized
in Table 2.
After extrusion, the tensile strength of the alloy at
room temperature reaches 310 MPa, and the elongation
rate reaches 12.3 %. At the temperature 423 K, the
tensile strength remains above 200 MPa, and shows good
high temperature plasticity, elongation is nearly 30 %.
The strength reduces as the temperature rises, but plas-
ticity increases obviously. Interestingly, there is no
obvious deterioration turning point of the strength as the
tensile temperature rises. Above all, the Mg-7Zn-
3Cu-1Ce magnesium alloy shows not only excellent
mechanical properties at room temperature, also good
mechanical properties in the moderate and elevated tem-
perature. It has great application potential as a heat-
Y. HU et al.: DEFORMATION BEHAVIOR OF THE Mg-7Zn-3Cu-1Ce ALLOY DURING HOT COMPRESSION
Materiali in tehnologije / Materials and technology 52 (2018) 2, 215–223 221
Figure 10: The effect of temperature on hot-compression microstructure of Mg-7Zn-3Cu-1Ce alloy between 573 K and 673 K at strain rate of
(0.01, 0.1, 1 and 10) s–1
Table 2: Mechanical properties of Mg-7Zn-3Cu-1Ce alloy at room
and elevated temperature.
Temperature b/MPa 0..2/MPa /%
273 K 310 270 12.3
423 K 202 185 28.5
448 K 170 152 30.5
473 K 146 137 37.5
resistant magnesium alloy with its excellent elevated
temperature performances and low cost.
4 CONCLUSIONS
1) The true stress level increases as the strain rate in-
creases at same deformation temperature, indicating
that alloy is a strain-rate sensitive material.
2) Under the condition of the same strain rate, there is
no obvious dynamic recrystallization phenomenon
during the process of hot compression, although the
true stress level decreases as the temperature rises. In
addition, the dynamic recovery is the main
influencing factor on the softening of the alloy.
3) By analysing the flow stress, we calculated some
basic material constants during high temperature
deformation, stress exponent n = 5.68 and hot
deformation activation energy Q = 1.91×102 kJ/mol.
We also established a constitutive equation for the
magnesium alloy by using the Z parameter:
Z RT
Z
= ⋅
=
⋅
⎛
⎝
⎜ ⎞
⎠
⎟



exp( . / )
ln
.
.
1 91 10
1
782 10
2
13
1
5 68
13
2
5 68
1
2
782 10
1+
⋅
⎛
⎝
⎜ ⎞
⎠
⎟ +
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥
⎧
⎨
⎪⎪
⎩
⎪
⎪
⎫
⎬
⎪⎪
⎭
⎪
⎪
⎧
Z
.
.⎨
⎪
⎪
⎩
⎪
⎪
4) After extrusion deformation at 673 K, the alloy
shows mechanical properties at room and elevated
temperature.
Acknowledgment
The authors are grateful for the financial support of
the National Key Research and Development Program of
China (No. 2016YFB0301100 and No. 2016YFB
0101600), and the Fundamental Research Funds for the
Central Universities of Chongqing University (No.
106112017CDJPT280001).
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