Materials Sciences and Applications, 2012, 3, 509-512
http://dx.doi.org/10.4236/msa.2012.38071 Published Online August 2012 (http://www.SciRP.org/journal/msa)
509
Influence of Thermomecaniques Treatments on the
Proprietes of Al-5.8%Zn-2.7%Mg Alloy
Mazouz Hamoudi, Bensaada Said, Mohamed Tewfik Bouziane
Laboratoire LARHYSS, Université de Biskra, Biskra, Algeria.
Received February 19th, 2012; revised April 15th, 2012; accepted June 11th, 2012
ABSTRACT
The aim of this work is the demonstration of the effect of thermomechanical treatments on the properties of the alloy
Al-5.8%Zn-2.7%Mg by thermal analysis techniques and calorimetry, which are methods of test widely used for
research purposes and quality control. The effects of thermomechanical treatments on the two variables namely the
coefficient of thermal expansion and heat capacity, we can provide further information for better understanding of the
phenomena responsible for the thermodynamic behavior of the alloy. The results showed the one hand, there is great
similarity between the linear coefficient of thermal expansion and heat capacity, and secondly the effect of plastic
deformation is evidenced by changes in the shape of the curves from the rough. Similarly the kinetics of precipitation of
η phase is accelerated in the case of samples homogenized and homogenized + distorted and accompanied by a shift in
the temperature range to lower temperatures than those recorded in the case of the material state Gross.
Keywords: Aluminum Alloys; Thermomechanical Treatments; Linear Coefficient of Thermal Dilation; Heat Capacity;
Precipitation
1. Introduction
Despite the importance of work in this area, aluminum
alloys continue to be the center of interest of several
research projects in materials science. Their use in the
automotive and aerospace industries depends heavily on
their mechanical and thermal characteristics. By using
different types of heat treatment and thermomechanical
can get a wide spectrum of mechanical properties. For
conditions of employment data, the thermomechanical
treatment of alloys requires a perfect knowledge of
changes in thermodynamic properties it entails.
The continuing development of modern techniques,
the complication and expansion of requirements to be
met by metal alloys have different properties and
qualities that are even today the study of thermome-
chanical processing is experiencing continued growth.
New modes of heat treatment, thermomechanical and
thermochemical alloys should be designed to meet the
requirements of modern industry. In this work, we pro-
pose to study the behavior dilatometry and calorimetry
(DSC) of the alloy Al-5.8%Zn-2.7%Mg in different
thermomechanical states.
2. Experimental Methods
The alloy Al-5.8%Zn-2.7%Mg was prepared by the con-
ventional method of casting ingots by melting in an
induction furnace from Leybold. The fusion is performed
in refractory crucibles (Al2O3). Its chemical composition
is shown in Table 1.
The temperatures and durations of heat treatments are
shown in Table 2.
The analytical techniques used in this regard are the
dilatometer and the DCS. It should be noted that all heat
treatments were performed in a furnace summers type
Adamel or the temperature gradient is about +/− 2˚C.
 The first sample is in the rough cast of [B] (Figure
1(a)).
 The second underwent a homogenization annealing
[H] at T = 465˚C and held for 20 hours, then quen-
ched in water (20˚C) (Figure 1(b)).
 The third sample, in addition to the homogenization
treatment, the alloy was cold rolled (Ε = 20%) [H + D]
(Figure 1(c)).
3. Results and Discussion
3.1. Dilatometric Study of the Sample in the
Rough
The Figure 2 shows the variation of the linear coefficient
of thermal expansion α of the alloy Al-5.8%Zn-2.7%Mg
in the raw state as a funcperature in the tion of tem

Influence of Thermomecaniques Treatments on the Proprietes of Al-5.8%Zn-2.7%Mg Alloy 510
Table 1. Chemical composition of the alloy Al-5.8%Zn-2.7%Mg.
Elément Al Zn Mg Cu Zr Fe Si
%en poids 91.45 5.8 2.7 0.01 0.01 0.01 0.01
Table 2. Temperature and duration of heat tr eatme nts.
Alliage Type des traitements thermiques Température (˚C) Temps de maintien (h)
Homogénéisation 465 20
Trempe 20
Al-5.8%Zn-2.7%Mg
Revenu 25 - 425 Variable
(a) (b) (c)
Figure 1. Microstructure of samples of the alloy Al-5.8%Zn-2.7%Mg: (a) Gross State (B); (b) State Homogenized (H) and (c)
Deformed State + Homogenized (H + D).
Transformations Domaine de température ˚C
Expansion 90 - 125
Contraction 175 - 225
Expansion 270 - 300
Expansion 350 - 400
Figure 2. Variation of α as a function of T ˚C of the alloy
Al-5.8%Zn-2.7%Mg in the rough.
interval [50˚C - 400˚C]. It is observed that occurs four
(04) transformations corresponding to different tempera-
ture ranges and is characterized by the peaks.
3.2. Calorimetric Study of the Sample in the
Rough
The Figure 3 shows the change in the DSC curve of the
alloy Al-5.8%Zn-2.7%Mg in the raw state as a function
of temperature and in the interval [50˚C - 400˚C].
It is observed that occurs three (03) transformations
corresponding to peaks:
One might think at first approach as the first three
transformations, there is a similarity between the results
found by both experimental techniques. There is a gap of
about twenty degrees C for there to be a perfect overlap
of the results found by the techniques of dilatometry and
calorimetry. The work of Deschamps et al. [1] and Ben-
abdoun [2] suggest that this discrepancy is certainly due
to poor calibration of the DSC. By cons for the fourth
processing corresponding to the third expansion observed
in the temperature range 350˚C - 400˚C, we find no
confirmation by a peak in this temperature range.
 The first peak, endothermic, is the first expansion ob-
served on the dilatometric curves and can be attri-
buted to the dissolution of Guinier and Preston zones

Influence of Thermomecaniques Treatments on the Proprietes of Al-5.8%Zn-2.7%Mg Alloy 511
Pics Domaine de température ˚C
Endothermique 100 - 140
Exothermique 200 - 240
Exothermique 260 - 280
Figure 3. Variation of the DCS as a function of T ˚C of the
alloy Al-5.8%Zn-2.7%Mg in the rough.
[3-7].
 The second peak, exothermic, one corresponding to
the contraction during the heating of the alloy in
question, in the field [50˚C - 400˚C], is probably due
to the appearance of the metastable phase η’ quoted
by Mondolfo et al. [8].
 The third exothermic peak recorded on the DSC curve
during heating of the alloy, corresponds perfectly to
the second expansion observed by dilatometry. This is
certainly related to the formation of the stable phase η
(MgZn) [9-11].
3.3. Influence of Thermomechanical Treatments
on the Expansion Curves Heat of the Alloy
Al-5.8%Zn-2.7%Mg
The Figure 4 shows the variation of the linear coefficient
of thermal expansion α of the alloy Al-5.8%Zn-2.7%Mg
as a function of temperature in the interval [50˚C - 400˚C]
for the three structural states studied (Gross, homo-
genized and Homogenized + Garbled).
It also notes that there is a slight shift in the tempe-
rature ranges corresponding to these phase transforma-
tions. The latter depend on the history of the material
before income and this confirms the work of Deschamps
[5] and Benabdoun [6].
3.4. Influence of Thermomechanical Treatments
on the DSC Curves Alloy
Al-5.8%Zn-2.7%Mg
Examination of the DSC thermograms (Figure 5) con-
Figure 4. Variation of α as a function of T ˚C of the alloy
Al-5.8%Zn-2.7%Mg for the three structural states.
Figure 5. Variation of the DCS as a function of T ˚C of the
Al-5.8%Zn-2.7%Mg alloy for the three structural states.
firms, quite clearly, the existence of at least three (03) of
these changes occurred during the tempering, the appear-
ance of three different peaks, while giving us additional
information on their intensity and nature of precipitation
or dissolution. It is found that these treatments have no
significant effect on the dissolution of GP zones (endo-
thermic peak corresponding to the first expansion) and
the precipitation of equilibrium phase η (MgZn) corres-
ponding to the second exothermic peak corresponding to
the second expansion recorded dilatometric curves. For
cons, the effects of heat treatment and homogenization in
particular those associated with plastic deformation are
visible by a shift to higher temperatures low precipitation
of the metastable phase η’. This is mainly due to defects
introduced during plastic deformation that significantly
enhance decomposition of the supersaturated solid solu-
tion. The increase in the number of gaps facilitates the
diffusion of atoms of magnesium and zinc, and the high
density of dislocations stimulates diffusion along the
channels of dislocations. Thus the activation energy of

Influence of Thermomecaniques Treatments on the Proprietes of Al-5.8%Zn-2.7%Mg Alloy 512
the reaction of precipitation of deformed samples is
much lower than that of samples with little or no dis-
tortion. Therefore the process of germination and growth
of new phases are favored.
On the other hand, the plastic deformation introduced
a supersaturated solid solution already containing an ex-
cess of defects due to the rapid quenching, further
increasing their density, and therefore encourages a
greater degree than the different phase transformations
may occur during heating of the material. This explains
why the phenomena related to the dissolution of the
zones, and precipitation of two phases η’ and η occur
earlier, at lower temperatures than for the case of the raw
material and/homogenized or that generally observed in
various aluminum alloys 7000 series.
4. Conclusions
The great diversity of phases present in alloys Al-Zn-Mg
makes this system very complex. They are likely to
improve physical properties by hardening or otherwise
alter significantly.
 Both technical analysis of thermodynamic properties
namely dilatometry and calorimetry may give us
additional information on the nature and sequence of
the various phenomena of precipitation or dissolution
of phases present during the tempering of the alloy
studied in the temperature range [50˚C - 400˚C].
 There is a great similarity between the curves of
thermal expansion and calorimetric study of the alloy.
 The first three transformations observed by the dila-
tometer technique namely the first two expansions
and the only contraction are directly related to the
appearance of different peaks recorded on the DSC
curves.
 The first expansion is directly related to one endo-
thermic peak appears on the DSC curves, it is cer-
tainly due to the dissolution of GP zones.
 The only contraction experienced by the material dur-
ing tempering is represented by the first exothermic
peak, the latter is due to the appearance of the
metastable phase η’.
 The second expansion corresponding to the second
exothermic peak may be due to the appearance of the
stable phase η (MgZn).
 The effects of heat treatment and homogenization in
particular those associated with plastic deformation
are highlighted by a shift toward lower temperatures
of the precipitation of metastable phase η’.
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