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Deformation structures and recrystallization behaviour of AlMn 1.04% alloy
Deformation Structures and Recrystallization Behaviour of AI-Mn 1.04% Alloy F. GATTO, G. CAMONA*, M. CONSERVA** AND P. FIORINI** Istituto Sperimentale dei Metalli Leggeri , Novara (Italy)
(Received January 15, 1968)
S UMMA R Y Deformation and recrystallization structures, as well as recrystallization kinetics, of an Al-Mn 1.04% alloy containin 9 Mn both in solid solution and as p.recipitate phase, have been investigated by optical and electron microscopy, X-rays and micro-hardness.
Results indicate that, on the whole, precipitate tends to influence deformation structures, whereas Mn in solid solution strongly controls recrystallization kinetics.
RESUME Les structures obtenues apr~s ~crouissage et aprks recristallisation ainsi que la cinOtique de recristallisation ont Ot~ ~tudiOes dans un alliage Al-1,04% Mn par microscopie optique et Olectronique, diffraction des rayons X et microduretk. Le manganbse Otait soit
en solution, soit prOcipitO. Les r~sultats montrent que les pr~cipit~s ont surtout pour influence de modifier partiellement les structures de dOformation, tandis que le mangankse en solution solide contr6le la cinOtique de recristallisation.
Z USA M M E N F A S S UNG Mit Hilfe optischer, elektronenmikroskopischer und r6ntgenographischer Verfahren sowie Mikrohdrte wurden Verformungs- und Rekristallisationsstrukturen sowie die Rekristallisationskirtetik einer Al1.04°//o Mn-Legierun9 mit Manoan in L6sun9 oder
INTRODUCTION
Among elements which affect the deformation and recrystallization behaviour of Al1'2, Mn has been recognized as one of the most efficient 3-6, its influence mostly depending on the supersaturation of the alloy and on size and distribution of the precipitate particles of MnA16 eventually present in the matrix. In this paper we report the result of a detailed investigation on deformation structures-and recrystallization kinetics o f A1-Mn 1.04% alloy (both single and two phase) performed by optical and electron microscopy, X-ray and hardness measurements.
als ausgeschiedene Phase untersucht. Die Ergebnisse lassen vermuten, dass die Ausscheidungen zum Teil die Verformungsstrukturen beeinflussen, wgihrend Mangan in L6sun9 stark die Rekristallisationskinetik bestimmt.
EXPERIMENTAL
The chemical composition of the alloy is given in Table 1. The chill cast material, after homogenization, was rolled to 5 .ram thickness. For further processing each sheet was divided in two parts: one part was solution treated at 620°C for 80 h in order to obtain a monophase alloy (in the following indicated as S.T., namely solution treated); the other part, after solubilization, was precipitation treated at 560°C for 48 h (in the follow-
* With CISE, Segrate (Milano), Italy. ** Formerly with C.N.R., Cinisello Balsamo (Milano), Italy.
Materials Science and Enoineerin9 - Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands
DEFORMATION STRUCTURES OF A 1 - M n
1 . 0 4 ALLOY
57
T A B L E 1 : COMPOSITIONOF THE INVESTIGATEDALLOY
Cu %
Fe %
Si %
Mn %
At %
0.003
0.015
0.015
1.04
98.927
ing indicated as P.T., namely precipitation treated), in order to obtain a dense dispersion of MnA16. The solubilization and precipitation procedures were performed according to previous resistometric workT; our solubilization procedure differs from that reported by other authors 6. Alloy sheet samples in both states (P.T. and S.T.) were rolled at room temperature at various degrees of deformation, H, ranging from 10 to 9 0 ~ (H is here defined as percent reduction in sample thickness). Deformation and recrystallization structures were investigated by electron microscopy; the recrystallization range for each deformation was investigated by X-ray techniques; finally recrystallization kinetics was determined by optical microscopy. All heat treatments were performed in molten salt baths, the temperature of which was kept constant to witl~in +2°C.
RESULTS AND ANALYSIS OF RESULTS
Deformation and recrystallization structures Deformation structures of the alloy in the S.T. state are shown by the electron micrographs shown in Fig. 1 (a, b, c). After low deformation ( H = 1 0 ~ , Fig. la) the material is characterized by isolated dislocation tangles; a weak cell structure occurs for H = 30~o (Fig. lb); a well defined cell structure appears for H = 5 0 ~ (Fig. lc) (regions where selected area diffraction indicated the presence of lattice misorienration have been interpreted as having a cell structure). The deformation structures of the P.T. state were reported in a previous paper8 ; a comparison between the latter and present results shows that the normal cell structure in the S.T. state occurs at lower deformation and its evolution by increasing deformation proceeds more regularly and homogeneously. Recrystallization structures after deformation H = 7 0 ~ are given in Figs. 2 (a, b, c) and 3 (a, b, c) for the S.T. and P.T. states, respectively.
Fig. 1. Distribution of dislocations in S.T. samples after deformation H = 2 0 % ( a ) ( × 1 6 0 0 0 ) , H = 3 0 ~ ( b ) ( × 2 6 0 0 0 ) , and H = 70% (c) ( x 10000).
Figure 2a shows that at 300°C the sub-grains have already a regular morphology, and their interior is comparatively dislocation-free. Mater. Sci. Eng., 3 (1968/69) 5(~61
58
F. GATTO e t al.
Fig. 2. Typical microstructures of S.T. samples after 1 hour annealing at 300°C (a) ( x 14000), 350°C (b) ( x 16000) and 370°C (c) ( x 20000).
Fig. 3. Typical microstructures of P.T. samples after 1 hour annealing at 310°C (a) ( x 16000), 350°C (b) ( x 6000) and 370°C (c) ( x 9000).
After an annealing at 350°C (Fig. 2b) a further thinning of sub-grain b o u n d a r i e s m a y be observed, but they are not yet high-angle boundaries, as is confirmed by electron-diffraction patterns. After
being annealed at 370°C (Fig. 2c) the sub-grains b e c o m e larger. Full recrystallization was seen to occur at 420°C. In P.T. samples, cell structure r e a r r a n g e m e n t Mater. Sci. Eng., 3 (1968/69) 56-61
DEFORMATION S T R U C T U R E S
was noticed already at 250°C; the process was more advanced at 310°C (Fig. 3a), where sub-grain growth and the thinning of sub-boundaries were clearly apparent. After the annealing at 350°C (Fig. 3b) a structure comprising well-recrystallized areas and unconsumed sub-grains was observed. The recrystallization of P.T. samples was complete at about 370°C (Fig. 3c). In conclusion, it should be pointed out that the recrystallization sequence is the same for both states, the process however being shifted towards higher temperatures in the S.T. samples.
Recrystallization kinetics
OF A 1 - M n
1 . 0 4 ALLOY
1.^
1.O x
0.5
Figure 4 shows the temperature-deformation plots corresponding to recrystallization commencement (lower curves) and recrystallization finish (upper curves) for both P.T. and S.T. states after 1 h annealing. Three deformation ranges can be envisaged : in the first, including values of H < 15~, both the beginning and end of recrystallization occur at lower temperatures in S.T. samples; in the second range, including H values of from 15~ to 40)/0, the beginning of recrystallization occurs at lower temperatures in P.T. samples, but the end of recrystallization is shifted to higher temperatures with respect to S.T. samples; finally, in the third range (H > 40~) both the beginning and end of recrystallization occur at higher temperatures in S.T. samples. Attention is drawn to the temperature--about 450° C--at which recrystallization beginning curves and recrystallization finish curves cut one another. 700 °C
600
59
"~ T
I i 0.1
1
Fig. 5. Plot of % recrystallization vs. time for S.T. samples (a) and for P.T. samples (b), after deformation H = 9 0 %
Isothermal reaction curves for P.T. and S.T. samples after deformation H=90~o are given in Fig. 5 (a and b, respectively). Experimental points were determined by optical microscopy, the fraction of recrystallized matrix being measured; in addition, the evolution of the recrystallization process was checked by Vickers micro-hardness measurements and by X-ray examination. Figure 6 (a and b) shows a plot of the log of the times t requ!red to obtain 30 and 50~ recrystallization vs. the reciprocal of the absolute temperature. As will be seen, the data follow an Arrhenius-type law: t = A e x p - (Q/RT),
(1)
A being a constant and Q the activation energy for recrystallization. Values obtained for Q are 60_ 6 kcal/mole for the P.T. state and 82+4 kcal/mole for the S.T. state, roughly independently of the recrystallization fraction. Data in Fig. 5 fit the Avrami relation 9 :
500
400
x = 1 - exp ( - B T) r 300
I 0
I 20
i
I 40
i
J 60
,
I 80
i
HO/o
I 1 O0
Fig. 4. Plot of recrystallization beginning and end temperatures vs. ~ deformation.
(2)
where x is the recrystallized fraction and B and K are constants, as indicated in Fig. 7 (a and b). The value of K is - 1 for both S.T. and P.T. states, Mater. Sci. Eng.,3 (1968/69) 56-61
F. GATTO et al.
60
rain
-- m m m - + ~
XI
I " 3 7 5 *C I o 365"C
m ,
m- - . * J i i i
10 x= 5ON*l° 7
J
.,~..- ~ f J f~.l
'
11~H_~t
/
'
k?'l
,4'V i .L.+ !.,.~z.
II
I t±
L ll - -/,,4-1 / !
/JI
0
1.50
1.52
1.54
001
1.56 10001.58 T
10 2
+ f~'
,
--
1
10
rain
Ib 2
I
10
rain
102
I~"
rain x=50O/o
10
~q
/J /f t f'g"
0.1 1.58
f
f
/~X=30
=/*
J
j~
f~
0 1.62
1.66
1.70
1000
1.76
0.1
T
Fig. 6. Arrhenius' plot for various per cents recrystallized in S.T. (a) and P.T. (b) samples after deformation H = 90%.
Fig. 7. Avrami's plots showing the isothermal transformations of S.T. (a) and P.T. (b) samples after deformation H = 9 0 ~ .
thus again indicating the occurrence of the same recrystallization mechanism. It was not possible to obtain isothermal recrystallization curves beyond H = 3 0 ~ for samples both in the P.T. and S.T. states, since the micro-optical observations did not allow clear distinction to be made between the recrystallized, recovered and highly deformed grains ; in addition, micro-hardness differences observed were too small. Therefore in this case we confined ourselves to the determination, by X-ray technique, of the times for the complete recrystallization at various temperatures (Fig. 8) in order to obtain the activation energy of the process. The values determined were : Q = 108 4- 6 kcal/mole for S.T. samples and Q= 1204-4 kcal/mole for P.T. samples. The actual activation energy values obtained for recrystallization after H =30 and H = 90~o confirm the behaviour shown by isochronal curves in Fig. 2.
state, especially at low deformation (b) Recrystallization mechanism is the same in both S.T. and P.T. states (c) Recrystallization kinetics is enhanced in the P.T. state after heavy deformation and in the S.T. state after low deformation. Point (a) can be explained by the role exerted by precipitate particles on the process of cell formation ; in accordance with the findings of other authors 1° M n m l 6 particles should hinder the aggregation of
~--
rnin
i
o P T Samples A ST Samples
,
--
/
10
/"
/
/"
/ .,/
/
x"
/
"
/
//
/
i"
J
J
/
DISCUSSION
The main results arising from the present investigation can be summarized as follows: (a) A dislocation cell structure after deformation is better defined in the S.T. state than in the P.T.
;
/
O,
I
1.26 1.28
1.30
1.32
1.34
1.36
1.38
1.40 1000 1.44 T
Fig. 8. Times and temperatures for complete recrystallization in S.T. and P.T. samples, after deformation H = 30%.
Mater. Sci.
Eng., 3 (1968/69) 56-61
DEFORMATION STRUCTURES OF A 1 - M n 1.04 ALLOY
dislocations of the same sign forming cell boundaries. With regard to point (b) it is stressed that no preferential nucleation of new grains at MnAI 6 particles was detected, contrary to the observation of other authors 6. Coming to point (c), first let us consider the mechanisms which can effect sub-grain boundary migration in both states. In P.T. alloy the hindering effect is obviously played only by precipitate particles and is independent of temperature as long as precipitate coalescence is negligible. In S.T. alloy the hindering effect is due to solute atoms forming a Cottrell atmosphere around dislocations constituting the boundaries la'x2; the density of solute within these atmospheres, hence the force opposing to the boundary migration, fall sharply with increasing temperature. Now, results reported in Fig. 4 indicate that the temperature above which Cottrell atmospheres fade out, being the ratecontrolling factor in S.T. alloy recrystallization, is about 450°C. Therefore in all cases where recrystallization temperature is shifted above 450°C (low deforma-
61
tion range) it is seen that recrystallization occurs more easily in S.T. samples; when the recrystallization temperature is below 450°C (case of high deformation) one observes the reverse.
REFERENCES 1 E. C. W. PERRYMAN,J. Metals, 7 (1955) 369. 2 C. RZEPSKI AND J. MONTOUELLE,Ecrouissage, restauration, recrystallization. Vllem Colloque de Metallurgie, Paris, 1963, p. 17. 3 G. MARGHAND,Can. J. Technol., 31 (1953) 15. 4 P. R. SPERRY, Trans. Am. Soc. Metals, 50 (1958) 589. 5 W. C. SETZER AND J. MORRIS, Trans. Am. Soc. Metals, 57 (1964) 589. 6 V. I. DOaATKIN AND YA. G. GRISHKOVETS,Metal. Sci. Heat Treat. Metals, 7 ~ (1966) 628. 7 A. FERRARI, P. FIORINI AND F. GATTO, Alluminio, 35 (1966) 223. 8 M. CONSERVAAND F. GA'rTO, Alluminio, 34 (1965) 401. 9 M. AVRAMI,J. Chem. Phys., 7 (1939) 1103; 8 (1940) 212; 9 (1941) 177. 10 P. R. SWANN,Electron Microscopy and Strength of Crystals. Wiley, New York, 1963, p. 131. 11 J. W. CAHN, Acta Met., 10 (1962) 789. 12 K. Li)CKE AND K. DETERT, Acta Met., 5 (1957) 628.
Mater. ScL Eng., 3 (1968/69) 56-61
(Received January 15, 1968)
S UMMA R Y Deformation and recrystallization structures, as well as recrystallization kinetics, of an Al-Mn 1.04% alloy containin 9 Mn both in solid solution and as p.recipitate phase, have been investigated by optical and electron microscopy, X-rays and micro-hardness.
Results indicate that, on the whole, precipitate tends to influence deformation structures, whereas Mn in solid solution strongly controls recrystallization kinetics.
RESUME Les structures obtenues apr~s ~crouissage et aprks recristallisation ainsi que la cinOtique de recristallisation ont Ot~ ~tudiOes dans un alliage Al-1,04% Mn par microscopie optique et Olectronique, diffraction des rayons X et microduretk. Le manganbse Otait soit
en solution, soit prOcipitO. Les r~sultats montrent que les pr~cipit~s ont surtout pour influence de modifier partiellement les structures de dOformation, tandis que le mangankse en solution solide contr6le la cinOtique de recristallisation.
Z USA M M E N F A S S UNG Mit Hilfe optischer, elektronenmikroskopischer und r6ntgenographischer Verfahren sowie Mikrohdrte wurden Verformungs- und Rekristallisationsstrukturen sowie die Rekristallisationskirtetik einer Al1.04°//o Mn-Legierun9 mit Manoan in L6sun9 oder
INTRODUCTION
Among elements which affect the deformation and recrystallization behaviour of Al1'2, Mn has been recognized as one of the most efficient 3-6, its influence mostly depending on the supersaturation of the alloy and on size and distribution of the precipitate particles of MnA16 eventually present in the matrix. In this paper we report the result of a detailed investigation on deformation structures-and recrystallization kinetics o f A1-Mn 1.04% alloy (both single and two phase) performed by optical and electron microscopy, X-ray and hardness measurements.
als ausgeschiedene Phase untersucht. Die Ergebnisse lassen vermuten, dass die Ausscheidungen zum Teil die Verformungsstrukturen beeinflussen, wgihrend Mangan in L6sun9 stark die Rekristallisationskinetik bestimmt.
EXPERIMENTAL
The chemical composition of the alloy is given in Table 1. The chill cast material, after homogenization, was rolled to 5 .ram thickness. For further processing each sheet was divided in two parts: one part was solution treated at 620°C for 80 h in order to obtain a monophase alloy (in the following indicated as S.T., namely solution treated); the other part, after solubilization, was precipitation treated at 560°C for 48 h (in the follow-
* With CISE, Segrate (Milano), Italy. ** Formerly with C.N.R., Cinisello Balsamo (Milano), Italy.
Materials Science and Enoineerin9 - Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands
DEFORMATION STRUCTURES OF A 1 - M n
1 . 0 4 ALLOY
57
T A B L E 1 : COMPOSITIONOF THE INVESTIGATEDALLOY
Cu %
Fe %
Si %
Mn %
At %
0.003
0.015
0.015
1.04
98.927
ing indicated as P.T., namely precipitation treated), in order to obtain a dense dispersion of MnA16. The solubilization and precipitation procedures were performed according to previous resistometric workT; our solubilization procedure differs from that reported by other authors 6. Alloy sheet samples in both states (P.T. and S.T.) were rolled at room temperature at various degrees of deformation, H, ranging from 10 to 9 0 ~ (H is here defined as percent reduction in sample thickness). Deformation and recrystallization structures were investigated by electron microscopy; the recrystallization range for each deformation was investigated by X-ray techniques; finally recrystallization kinetics was determined by optical microscopy. All heat treatments were performed in molten salt baths, the temperature of which was kept constant to witl~in +2°C.
RESULTS AND ANALYSIS OF RESULTS
Deformation and recrystallization structures Deformation structures of the alloy in the S.T. state are shown by the electron micrographs shown in Fig. 1 (a, b, c). After low deformation ( H = 1 0 ~ , Fig. la) the material is characterized by isolated dislocation tangles; a weak cell structure occurs for H = 30~o (Fig. lb); a well defined cell structure appears for H = 5 0 ~ (Fig. lc) (regions where selected area diffraction indicated the presence of lattice misorienration have been interpreted as having a cell structure). The deformation structures of the P.T. state were reported in a previous paper8 ; a comparison between the latter and present results shows that the normal cell structure in the S.T. state occurs at lower deformation and its evolution by increasing deformation proceeds more regularly and homogeneously. Recrystallization structures after deformation H = 7 0 ~ are given in Figs. 2 (a, b, c) and 3 (a, b, c) for the S.T. and P.T. states, respectively.
Fig. 1. Distribution of dislocations in S.T. samples after deformation H = 2 0 % ( a ) ( × 1 6 0 0 0 ) , H = 3 0 ~ ( b ) ( × 2 6 0 0 0 ) , and H = 70% (c) ( x 10000).
Figure 2a shows that at 300°C the sub-grains have already a regular morphology, and their interior is comparatively dislocation-free. Mater. Sci. Eng., 3 (1968/69) 5(~61
58
F. GATTO e t al.
Fig. 2. Typical microstructures of S.T. samples after 1 hour annealing at 300°C (a) ( x 14000), 350°C (b) ( x 16000) and 370°C (c) ( x 20000).
Fig. 3. Typical microstructures of P.T. samples after 1 hour annealing at 310°C (a) ( x 16000), 350°C (b) ( x 6000) and 370°C (c) ( x 9000).
After an annealing at 350°C (Fig. 2b) a further thinning of sub-grain b o u n d a r i e s m a y be observed, but they are not yet high-angle boundaries, as is confirmed by electron-diffraction patterns. After
being annealed at 370°C (Fig. 2c) the sub-grains b e c o m e larger. Full recrystallization was seen to occur at 420°C. In P.T. samples, cell structure r e a r r a n g e m e n t Mater. Sci. Eng., 3 (1968/69) 56-61
DEFORMATION S T R U C T U R E S
was noticed already at 250°C; the process was more advanced at 310°C (Fig. 3a), where sub-grain growth and the thinning of sub-boundaries were clearly apparent. After the annealing at 350°C (Fig. 3b) a structure comprising well-recrystallized areas and unconsumed sub-grains was observed. The recrystallization of P.T. samples was complete at about 370°C (Fig. 3c). In conclusion, it should be pointed out that the recrystallization sequence is the same for both states, the process however being shifted towards higher temperatures in the S.T. samples.
Recrystallization kinetics
OF A 1 - M n
1 . 0 4 ALLOY
1.^
1.O x
0.5
Figure 4 shows the temperature-deformation plots corresponding to recrystallization commencement (lower curves) and recrystallization finish (upper curves) for both P.T. and S.T. states after 1 h annealing. Three deformation ranges can be envisaged : in the first, including values of H < 15~, both the beginning and end of recrystallization occur at lower temperatures in S.T. samples; in the second range, including H values of from 15~ to 40)/0, the beginning of recrystallization occurs at lower temperatures in P.T. samples, but the end of recrystallization is shifted to higher temperatures with respect to S.T. samples; finally, in the third range (H > 40~) both the beginning and end of recrystallization occur at higher temperatures in S.T. samples. Attention is drawn to the temperature--about 450° C--at which recrystallization beginning curves and recrystallization finish curves cut one another. 700 °C
600
59
"~ T
I i 0.1
1
Fig. 5. Plot of % recrystallization vs. time for S.T. samples (a) and for P.T. samples (b), after deformation H = 9 0 %
Isothermal reaction curves for P.T. and S.T. samples after deformation H=90~o are given in Fig. 5 (a and b, respectively). Experimental points were determined by optical microscopy, the fraction of recrystallized matrix being measured; in addition, the evolution of the recrystallization process was checked by Vickers micro-hardness measurements and by X-ray examination. Figure 6 (a and b) shows a plot of the log of the times t requ!red to obtain 30 and 50~ recrystallization vs. the reciprocal of the absolute temperature. As will be seen, the data follow an Arrhenius-type law: t = A e x p - (Q/RT),
(1)
A being a constant and Q the activation energy for recrystallization. Values obtained for Q are 60_ 6 kcal/mole for the P.T. state and 82+4 kcal/mole for the S.T. state, roughly independently of the recrystallization fraction. Data in Fig. 5 fit the Avrami relation 9 :
500
400
x = 1 - exp ( - B T) r 300
I 0
I 20
i
I 40
i
J 60
,
I 80
i
HO/o
I 1 O0
Fig. 4. Plot of recrystallization beginning and end temperatures vs. ~ deformation.
(2)
where x is the recrystallized fraction and B and K are constants, as indicated in Fig. 7 (a and b). The value of K is - 1 for both S.T. and P.T. states, Mater. Sci. Eng.,3 (1968/69) 56-61
F. GATTO et al.
60
rain
-- m m m - + ~
XI
I " 3 7 5 *C I o 365"C
m ,
m- - . * J i i i
10 x= 5ON*l° 7
J
.,~..- ~ f J f~.l
'
11~H_~t
/
'
k?'l
,4'V i .L.+ !.,.~z.
II
I t±
L ll - -/,,4-1 / !
/JI
0
1.50
1.52
1.54
001
1.56 10001.58 T
10 2
+ f~'
,
--
1
10
rain
Ib 2
I
10
rain
102
I~"
rain x=50O/o
10
~q
/J /f t f'g"
0.1 1.58
f
f
/~X=30
=/*
J
j~
f~
0 1.62
1.66
1.70
1000
1.76
0.1
T
Fig. 6. Arrhenius' plot for various per cents recrystallized in S.T. (a) and P.T. (b) samples after deformation H = 90%.
Fig. 7. Avrami's plots showing the isothermal transformations of S.T. (a) and P.T. (b) samples after deformation H = 9 0 ~ .
thus again indicating the occurrence of the same recrystallization mechanism. It was not possible to obtain isothermal recrystallization curves beyond H = 3 0 ~ for samples both in the P.T. and S.T. states, since the micro-optical observations did not allow clear distinction to be made between the recrystallized, recovered and highly deformed grains ; in addition, micro-hardness differences observed were too small. Therefore in this case we confined ourselves to the determination, by X-ray technique, of the times for the complete recrystallization at various temperatures (Fig. 8) in order to obtain the activation energy of the process. The values determined were : Q = 108 4- 6 kcal/mole for S.T. samples and Q= 1204-4 kcal/mole for P.T. samples. The actual activation energy values obtained for recrystallization after H =30 and H = 90~o confirm the behaviour shown by isochronal curves in Fig. 2.
state, especially at low deformation (b) Recrystallization mechanism is the same in both S.T. and P.T. states (c) Recrystallization kinetics is enhanced in the P.T. state after heavy deformation and in the S.T. state after low deformation. Point (a) can be explained by the role exerted by precipitate particles on the process of cell formation ; in accordance with the findings of other authors 1° M n m l 6 particles should hinder the aggregation of
~--
rnin
i
o P T Samples A ST Samples
,
--
/
10
/"
/
/"
/ .,/
/
x"
/
"
/
//
/
i"
J
J
/
DISCUSSION
The main results arising from the present investigation can be summarized as follows: (a) A dislocation cell structure after deformation is better defined in the S.T. state than in the P.T.
;
/
O,
I
1.26 1.28
1.30
1.32
1.34
1.36
1.38
1.40 1000 1.44 T
Fig. 8. Times and temperatures for complete recrystallization in S.T. and P.T. samples, after deformation H = 30%.
Mater. Sci.
Eng., 3 (1968/69) 56-61
DEFORMATION STRUCTURES OF A 1 - M n 1.04 ALLOY
dislocations of the same sign forming cell boundaries. With regard to point (b) it is stressed that no preferential nucleation of new grains at MnAI 6 particles was detected, contrary to the observation of other authors 6. Coming to point (c), first let us consider the mechanisms which can effect sub-grain boundary migration in both states. In P.T. alloy the hindering effect is obviously played only by precipitate particles and is independent of temperature as long as precipitate coalescence is negligible. In S.T. alloy the hindering effect is due to solute atoms forming a Cottrell atmosphere around dislocations constituting the boundaries la'x2; the density of solute within these atmospheres, hence the force opposing to the boundary migration, fall sharply with increasing temperature. Now, results reported in Fig. 4 indicate that the temperature above which Cottrell atmospheres fade out, being the ratecontrolling factor in S.T. alloy recrystallization, is about 450°C. Therefore in all cases where recrystallization temperature is shifted above 450°C (low deforma-
61
tion range) it is seen that recrystallization occurs more easily in S.T. samples; when the recrystallization temperature is below 450°C (case of high deformation) one observes the reverse.
REFERENCES 1 E. C. W. PERRYMAN,J. Metals, 7 (1955) 369. 2 C. RZEPSKI AND J. MONTOUELLE,Ecrouissage, restauration, recrystallization. Vllem Colloque de Metallurgie, Paris, 1963, p. 17. 3 G. MARGHAND,Can. J. Technol., 31 (1953) 15. 4 P. R. SPERRY, Trans. Am. Soc. Metals, 50 (1958) 589. 5 W. C. SETZER AND J. MORRIS, Trans. Am. Soc. Metals, 57 (1964) 589. 6 V. I. DOaATKIN AND YA. G. GRISHKOVETS,Metal. Sci. Heat Treat. Metals, 7 ~ (1966) 628. 7 A. FERRARI, P. FIORINI AND F. GATTO, Alluminio, 35 (1966) 223. 8 M. CONSERVAAND F. GA'rTO, Alluminio, 34 (1965) 401. 9 M. AVRAMI,J. Chem. Phys., 7 (1939) 1103; 8 (1940) 212; 9 (1941) 177. 10 P. R. SWANN,Electron Microscopy and Strength of Crystals. Wiley, New York, 1963, p. 131. 11 J. W. CAHN, Acta Met., 10 (1962) 789. 12 K. Li)CKE AND K. DETERT, Acta Met., 5 (1957) 628.
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