INFLUENCE OF THE ADDITION OF TIN IN THE STATE OF
TRACKS ON THE KINETICS OF PRECIPITATION IN THE
ALLOY Al-Ag
F. LOURDJANE *, A. RAHO,
Lourdjane_faiza@yahoo.fr, raho_ azzeddine@yahoo.fr
University of Sciences and the Technology HOUARI BOUMEDIENE,BP 32 ALLIA BAB EZZOUAR ALGIERS.
Faculty of physics, USTHB
Abstract
In this study, we are study the influence to addition the tin on the kinetics of formation of the G.P zones in Al-Ag alloy. The precipitation of
the G.P zones is governed by diffusion of atoms of solution. Their kinetics of the precipitations is influence by the thermal excitement and the
concentration to the gaps in alloy. In this study. We establish kinetics of precipitation of the G.P zones in Al-Ag and Al-Ag-Sn alloys by a
method based on the microhardness. The presence of Sn results in a retarding effect on the G.P zones formation.
Keywords: G.P zone, precipitation.
1. Introduction
A supersaturated solid solution Al-Ag evolves towards the balance
characterized by the precipitation of the equilibrium phase δ(Ag2Al)
according to the sequence
3. Results and discussion
DSC scans recorded at 2°C min-1 for two samples Al-39wt%Ag,
Al-39wt%Ag-0.05%Sn alloys wish have been homogenized 72h
at 540°C and quenched (fig.1) showed the following:
 *    G.Pzones     ' phase     phase [1,
2]
0,06
Where α* is the supersaturated solid solution, G.P Guinier – Preston
zones is heap of atoms of silver. These zones are coherent with the
matrix network, δ’ is a metastable phase semi-coherent and δ is the
Ag2Al equilibrium precipitate, incoherent with the matrix network,
is soothing.
The precipitation of zones G.P governed by the diffusion of atoms
of solution, is favored by the presence of gaps and the rise of the
temperature.
In this paper, we are propose to study the effect of Sn in the state of
tracks on the kinetics of formation of the G.P zones for different
temperature of ageing at [90-150]°C by method based on the
microhardness.
2. Experimental
Our Al-39wt.%Ag, Al-39wt.%Ag-0.05%Sn alloys were prepared
by fusion of Aluminum and Silver are pure 99,99 at temperature
1000°C. The samples are homogenizing at 540°C however 72
hours, and quenched in water. The samples obtained were analyzed
by EDAX. Samples for calorimetric measurements were of 1.5 mm
thickness. The calorimetric measurements were performed with a
METLER TA 400 DSC. A protective atmosphere of pure argon
was used. The Vickers microhardness were determined on the
samples under a load of 100g, by using microhardness
measurements [SHIMADZU].
DSC
0,04
0,02
Al39% Ag0.05Sn
Al39% Ag
dQ/dT
0,00
-0,02
-0,04
-0,06
-0,08
-0,10
-0,12
-0,14
T(°C)
-0,16
0
50
100
150
200
250
300
350
400
Fig.1. DSC scans of Al-39wt.%Ag and Al-39wt.%Ag-0.05%Sn alloys homogenized
for 72h at 540°C.
A) Case of Al39wt.%Ag alloy:
1.
an endothermic effect in the temperature range [170200]°C due certainly to the dissolution of GP zones.
2.
an exothermic peak between [240-300]°C due to the
precipitation of phases δ’and δ.
B)
Case of Al39wt.%Ag-0.05Sn alloy:
1.
An endothermic between [150-194]°C thing that
Al39%Ag alloy to the dissolution of GP zones.
An exothermic peak between [230-310]°C due to the
precipitation of phases δ’and δ.
2.
185
T=125°C
Al39% Ag
Al39% Ag0.05Sn
180
220
210
HV
200
175
T=200°C
Al39% Ag
Al39% Ag 0.05Sn
HV
170
165
190
160
180
155
150
170
145
160
140
t(h)
150
0,01
0,1
1
10
100
140
t(h)
130
0,01
0,1
1
10
100
Fig.2.Vickers microhardness curves for Al-39wt.%Ag and Al-39wt.%Ag0.015wt.%Sn alloys at 200°C.
The isotherms of hardness, in the temperature T=200°C (Fig.2) in
first time, show a softening due to the dissolution of G.P zones.
Fig.3.b. Vickers microhardness curves for Al-39wt.%Ag and Al39wt.%Ag-0.015wt.%Sn alloys at 125°C.
185
180
The isotherms of hardness, established for samples Al-39wt.%Ag,
Al-39wt. %Ag-0.05Sn alloys, for different ageing at [90-150]°C
(Fig.3.(a).(b).(c)), show hardness due to the G.P zones formed just
after quenching.
The landing (plateau) correspond of equilibrium metastable to the
precipitation G.P zones, where the volume fraction is maximal.
The precipitation of phase metasteble δ’ hardness alloy, the decline
in hardness was thus probably associated with formation of
equilibrium phase δ.
HV
T=150°C
Al39% Ag
Al39% Ag 0.05Sn
175
170
165
160
155
150
145
t(h)
140
0,01
0,1
1
10
200
190
180
Fig.3.c. Vickers microhardness curves for Al-39wt.%Ag and Al39wt.%Ag-0.015wt.%Sn alloys at 150°C.
T=90°C
Al39% Ag
Al39% Ag0.05Sn
HV
The transformed fraction, F, representing the volume occupied by
the G.P zones during the heat treatment of ageing reported to the
volume which they occupy to the equilibrium metastable, based
on MERLE relation:
170
160
HV (t) =F.HV (equilibrium metastable) + (1-F). HV (0) [3].
150
140
0,01
t(h)
0,1
1
10
100
Where HV (t) is the hardness each treatment time t, HV
(equilibrium metastable) is the maximum hardness obtained in
which the G.P zones occupy a maximum volume and HV(0) is the
hardness of T=90°C
the as-quenched solid solution.
Al39% Ag
The 1,0
kinetics
isothermal
are kept of ageing at [90-150]°C give the
F
Fig.3.a. Vickers microhardness curves for Al-39wt.%Ag and Al39wt.%Ag-0.015wt.%Sn alloys at 90°C.
Al39% Ag0.05Sn
phases of the germinate, growth and coalescence.
The 0,8
τ incubation time of G.P zones (Fig.4. (a).(b).(c)), establish
by extrapolation, they are characteristic of germinate fast on
reason
oversaturation of vacancies just after quenching.
0,6
The phases of growth and coalescence are slower on reason of
elimination of a party of the vacancies in excess obtained in the
0,4
quenching. HV(t) this isotherms fig(3) show, when Sn is in the
solid solution a decrease of the life of the G.P zones.
0,2
t(h)
1E-3
0,01
0,1
1
10
210
1,1
1,0
F
T=90°C
Al39% Ag
Al39% Ag0.05Sn
T=150°C
Al39% Ag
Al39% Ag0.05Sn
1,0
0,9
F
0,8
0,8
0,7
0,6
0,6
0,5
0,4
0,4
0,3
0,2
t(h)
1E-3
0,01
0,1
1
0,2
t(h)
10
0,1
1E-3
0,01
0,1
1
10
Fig.4.a Kinetics isotherms of precipitation of the G.P zones in the Al39wt.%Ag and Al-39wt.%Ag-0.015wt.%Sn alloy s at T=90°C.
Fig.4.c Kinetics isotherms of precipitation of the G.P zones in the Al39wt.%Ag and Al-39wt .%Ag-0.015wt.%Sn alloy s at T=150°C.
0,8
Time of incubation obtained allow to determine from the relation of
Arrhenius; activation energy to the diffusion during the transformation,
defined by [4].
t= B exp (Q/RT)
Where Q is the activation energy of the transformation, R is the constant of
perfect gaze; T is the temperature and B the constant
T=125°C
Al39% Ag
Al39% Ag0.05Sn
1,0
F
0,6
-3,0
Al39% Ag
Al39% Ag 0.02Sn
-3,2
0,4
-3,4
-3,6
Lnti (h)
0,2
-3,8
-4,0
t(h)
0,0
1E-3
0,01
0,1
1
10
-4,2
-4,4
-4,6
-1
1/T(K )
Fig.4.b Kinetics isotherms of precipitation of the G.P zones in the Al39wt.%Ag and Al-39wt.%Ag-0.015wt.%Sn alloys at T=125°C .
-4,8
0,0023
0,0024
0,0025
0,0026
0,0027
0,0028
Fig.4.d Determination of the energies of activation to the diffusion during
germinates of the G.P zones.
Al-39wt.%Ag
Q= 8 KJ
Al-39wt.%Ag-0.015wt.%Sn
Q= 31 KJ
This low energy to compared that of diffusion silver in the aluminum pure
Q=100KJ/mol is characteristic of germinate fast on reason
oversaturation of vacancies just after quenching.
0,4
0,2
0,0
-0,2
-0,4
-0,6
0,6
-0,8
0,4
T=90°C
Al39% Ag
Al39% Ag0.05Sn
Data1D
Data1B
1,0
0,5
0,0
-1,0
0,0
-1,2
-0,2
-1,4
-0,4
-1,6
ln(ln(1/1-F))
-0,5
-1,0
0,2
-0,6
-0,8
T=150°C
Al39% Ag
Al39 % Ag0.05Sn
Data1B
Data1D
ln(ln(1/1-F))
0,6
T=150°C
Al39% Ag
Al39 % Ag0.05Sn
Data1B
Data1D
ln(ln(1/1-F))
The kinetics isothermal are kept of ageing at [90-150]°C, (Fig.
5.(a);(b);(c))show the effect to addition as trace of the tin on the
precipitation the G.P zones. It traps some present vacancies in
alloys, the atoms of tin are responsible a retarding effect of the G.P
zones formation.
The curves log(log(1/1-F)) are characteristic of growth is defined
by JMAK equation[5,6,7]. The growth check by the diffusion
F(t)=1-exp(-kt)n
Where n and k are the parameters of growth.
lnt(h)
-4,0 -3,8 -3,6 -3,4 -3,2 -3,0 -2,8 -2,6 -2,4 -2,2 -2,0 -1,8 -1,6
-1,0
-1,2
Fig.5.cDetermination
of the parameters of growths in the Al-39wt.%Ag
and -1,4
Al-39wt.%Ag-0.015wt.%Sn at T=150°C.
-1,5
lnt(h)
-1,6
-2,0
-4,0
-3,8
-3,6
-3,4
-3,2
-3,0
-2,8
-2,6
-2,4
-2,2
-2,0
-1,8
-1,6
lnt(h)
-2,5
-4,0
-3,5
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
0,0
Al-39wt.%Ag
Fig.5.a Determination of the parameters of growths in the Al-39wt.%Ag
and Al-39wt.%Ag-0.015wt.%Sn at T=90°C.
90°C
125°C
150°C
n
0.80
0.82
1.08
k
8.47
11.47
16.42
Al-39wt.%Ag-0.05Sn
n
0.84
1.0
0.94
k
4.87
9.29
11.24
Table-1-Parameters of growth
1,5
0,5
0,0
ln(ln(1/1-F))
1,0
T=125°C
Al39% Ag
Al39% Ag0.05Sn
Data1B
Data1D
The parameters n are characteristic of heterogeneous the G.P zones
The parameter k, characteristic the transformation speed, defined by
k=A exp(-Q/KT).
4. Conclusions
-0,5
-1,0
-1,5
-2,0
lnt(h)
-4,0
-3,5
-3,0
-2,5
-2,0
-1,5
-1,0
-0,5
Fig.5.bDetermination of the parameters of growths in the Al-39wt.%Ag
and Al-39wt.%Ag-0.015wt.%Sn at T=125°C.
The isotherms of hardness, established in various temperatures,
highlighted the precipitation of G.P zones, the metastable phase δ’ and the
equilibrium precipitate δ.
The establishment of the isothermal kinetics allowed to determine the
visible energies of activation of the diffusion during the germinating and
during the growth of G.P zones.
The parameters of growth were determined during the growth of G.P
zones.
The isothermal kinetics showed that the addition of tin results a retarding
effect on the G.P zones formation.
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