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High strain rate superplasticity of a SiC particulate reinforced aluminium alloy composite by a vortex method
Pergamon
Scripta Metallurgica
et
Materialia, Vol. 31, No. 9, pp. 1181-1186, 1994 Copyright © 1994 Elsevier Science Ltd Printed in the USA. All rights reserved 0956-716X/94 $6.00 + 00
HIGH STRAIN RATE SUPERPLASTICITY OF A SiC PARTICULATE REINFORCED ALUMINIUM ALLOY COMPOSITE BY A VORTEX METHOD Takeo Hikosaka*, Tsunemichi Imai**, T.G.Nieh **and Jeff Wadsworth*** * Industrial Research Institute, Aichi Prefectural Government, Nishishinwari Hitotsuki, Kariya City, Aichi 448, Japan ** National Industrial Research Institute of Nagoya, 1 Hirate-cho, Kita-ku, Nagoya 462, Japan *** Lawrence Livermore National Laboratory, P.O.Box 808, Livermore, CA 94551-9900, U.S.A. (Received May 3, 1994) (Revised June 13, 1994)
Introduction High strain rate superplasticity (HSRS) for ceramic whisker or particulate reinforced aluminium alloy composites exhibiting a total elongation of 250-600% at a high strain rate such as 0.1-10S -l is expected to establish an efficient, near-net shape forming for automobile engineering components, aerospace structures and semi-conductor packagings (111). The composites can be fabricated by squeeze casting, the vortex method and compocasting, the powder metallurgical (P/M) method and spray deposition. Casting processes such as squeeze casting, compocasting and the vortex method are cost-effective. The composites fabricated by casting processes have already been applied to automobile engine components, satellite components and the like (12). Cast aluminium alloy composites have serious problems for practical application in that their tensile ductility and fracture toughness at room temperature are significantly poor and their relatively large ceramic particles make them too hard. These problems encourage the establishment of a secondary fabrication process which can efficiently produce engineering components of a cast aluminium alloy composite. The ceramic particulates reinforced aluminium alloy composites which can produce HSRS have been fabricated primarily by a P/M method. However, the superplastic aluminium alloy P/M composites are too expensive for use in non-military engineering components (1). A vortex method has been used to produce a metal matrix composite in which agglomerated particles and several defects result in poor quality. Thus, it is important to improve fabrication processing in order to make fine ceramic particles dispersed homogeneously and to remove defects in the composite. The purpose of this study is to establish thermomechanical processing to build fine microstructure and to produce HSRS for a SiC particulate reinforced aluminium alloy composite fabricated by a voltex method and to make clear the superplastic characteristics. 1181
1182
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Vol. 31, No. 9
Experimental Procedure SiC particles (the average particle size of dso=0.61am) were used as reinforcement materials. Table 1 shows the chemical compositions of the SiC particles and 6061 aluminium alloy. The molten 6061 aluminium alloy heated at 1023K was stirred with the heating SiC particles and 0.3%wt-calcium at a rotating speed of 500-700rpm in a crucible for 90 minutes by vortex method equipment. The volume fraction of the SiC particle was about Vf=0.20. The as-cast composite was reforged at 1123K in an atmosphere under the pressure of 100MPa by a squeeze casting machine. The mold was heated at 623K. Thermomechanical processings used to produce HSRS for the composite was hot rolling after extrusion. Hot extrusion was performed with the extrusion ratio of 56 at 623K. After heating at 798K, the composite was hot-rolled. The thickness reduction of each rolling pass was 0.5mm and the reheating-holding time between rolling passes was about 5 minutes. The final thickness of the composite hot-rolled was about 0.75mm. Tensile specimens with a 4mm gage width and a 5.5mm gage length were pulled at 853K and in the strain rate region from 0.01 to about 2S--1. The microstructure and fracture surface were observed by TEM and SEM. Experimental Results and Discussion Figures 1 show optical microstructures of the SiCp/6061 aluminium alloy composites (a) squeeze casting after a vortex method and (b) hot-rolled after a vortex method, squeeze casting and extrusion, respectively. SiC particle size was dispersed homogeneously in the SiCp/6061 AI composite hot-rolled after the vortex method, squeeze casting and extrusion although an aluminium alloy layer and some agglomerated SiC particles appear in the asextruded composite. A relationship between a flow stress (or) and a true strain rate (e) in superplastic materials can be expressed as the equation o=Ke ~, where K is a constant. It is necessary to find optimum testing temperature and optimum strain rate in which the strain rate sensitivity of a flow stress, m-value, is larger than 0.3 because a higher m value suppresses the development of necking and leads to higher total elongation. Figure 2 shows the relationship between the flow stress and the strain rate of the SiCp/6061 aluminum alloy composite fabricated by the vortex method before squeeze casting, extrusion and hot rolling. The flow stress in the composite increases linearly with a raising strain rate and the strain rate sensitivity of the flow stress (the m value) shows about 0.33 in the strain rate region from 0.1S -~ up to 1.3S-1 and at 833K, but the m value becomes less than 0.3 in the strain rate less than 1.0S-1 . Total elongation of the composite is shown in Fig. 3. The superplastically deformed SiCp/6061 AI composite in which maximum total elongation of about 200% was obtained is shown in Fig.4. The total elongation of the SiCp/6061 AI composite became about 200% in the strain rate region from 0.1S ~ to 0.3S -I and the total elongation more than 100% was obtained in the wide strain rate region from 0.01S ~up to 0.gs -j . The result indicates that defects in the SIC/6061 aluminium alloy composite fabricated by the vortex method can be removed by squeeze casting, and hot rolling after extrusion has a significant effect on making finer SiC particles dispersed homogeneously.
Vol. 31, No. 9
SUPERPLASTICITY COMPOSITE
1183
The superplastic deformation mechanism includes fine grain boundary sliding, interfacial sliding at a liquid phase and dynamic recrystallization. The m value of 0.33 in Fig.2 shows that the SiCp/6061 A1 composites could produce HSRS predominantly by fine grain boundary sliding. Figure 5 shows the flow stress-true strain curves of the SiCp/6061 AI composite fabricated by the vortex method and squeeze casting before extrusion and hot rolling. The maximum flow stress increases with a raising strain rate and, strain hardening and softening in these flow stress-true strain curves are not so high; therefore, continuous recrystallization of the SIC/6061 A1 composite may be accomplished during hot rolling and extrusion. A fracture surface of the SiCp/6061 AI composites hot-rolled after extrusion, the vortex method and squeeze casting is shown in Fig. 6. The strain rate and the total elongation of the composite are 0.13S -1 and about 200%, respectively. The fracture surface of the composite has a partially melted matrix although the composite was deformed just below the solidus temperature of the 6061 aluminium matrix, and filaments appear on the fracture surface. The diameter of the filaments in the SiCp/6061 AI composite is very fine due to the finer relative distance between SiC particles. The filament should be related to a semi-liquid phase at or near a SiCp/6061 interface since the semi-liquid layer at the interface between the matrix and the SiC particle could be elongated significantly during hot rolling and superplastic deformation. The Mg segregation in the SiCp/6061 AI composite should occur because the SIC/6061 AI composite was deformed with a matrix and at the interface in a partially liquid phase condition (9, 10). The SiCp/6061 AI composite can achieve the high total elongation of about 200% by interfacial sliding at a liquid phase in addition to fine grain boundary sliding. Conclusions SiCp/6061 AI alloy composites fabricated by a vortex method and squeeze casting were hot-rolled after extrusion and the superplastic chracteristics of the composite were investigated. The following results were obtained: (l)The strain rate sensitivity (m value) of the SiCp/6061 AI composites is 0.33. (2)The SiCp/6061 AI composite hot-rolled and extruded after the vortex mehtod and squeeze casting exhibited the total elongation of 200% in strain rates from 0.13S -1 to 0.3 S-1 at 853K. (3)The fracture surface of the composite has a partially liquid phase although the composite was deformed just below the solidus temperature of the 6061 matrix and filaments appeared, lnterfacial sliding at the liquid phase contributes to HSRS in addition to fine grain boundary sliding. References 1. T.G.Nieh, C.A.Henshall and J.Wadsworth, Scripta Metallurgica, 18-12(1984) 1405/1408 2. M.W.Mahoney and A.K.Ghosh, Metall. Trans, 18A(1987) 653/661 3. T.Imai, M.Mabuchi, Y.Tozawa and M.Yamada,J.Materials Science letters, 9(1990) 255/257 4. M.Mabuchi, T.Imai, K.Kubo, H.Higashi, Y.Obada and T.Tanimura, Materials Letters,11,12(1991)339/342
1184
SUPERPLASTICITY COMPOSITE
Vol. 31, No. 9
5.
M.Mabuchi, K.Higashi, Y.Okada, S.Tanimura, T.Imai and K.Kubo,Scripta Metallurgica et Materialia, 25(1991)2517/2522 6. T.Imai, M.Mabuchi and T.Tozawa, Superplasticity in Advanced Materials, edited by S.Hori,M.Tokizane and N.Furushiro(A Publication of JSRS, 1991)373/378 7. T.Tsuzuki and A.Takahashi, Proc. of 1st Japan International SAMPE Symposium (Nov.28-Decl, 1989)243 8. T.G.Nieh and J.Wadsworth, Superplasticity in Advanced Materials, edited by S.Hori, M.Tokizane and N.Furushiro(A Publication of JSRS, 1991)339/348 9. G.L'Esperance, T.Imai and B.Hong, ibid, 379/384 10. T.Imai, G.L'Esperance, B.Hong, M.Mabuchi, and Y.Tozawa, Advances in Powder Metallurgy & Particulate Materials-1992, compiled by J.M.Caus and R.M.German, 9(1992) 181/194 11. T.lmai, G.L'Esperance & B.D.Hong, Scripta Metall.et Mate., accepted 12. S.Kennerknecht, Fabrication of Particulate Reinforced Metal Composites, edited by J.Masounave & F.G.Hamel, (1990, published by ASM International)87/100 Acknowledgment The financial support of the New Enegy and Industrial Technology Development Organization (NEDO) of Japan is greatly acknowledged. And this work was, in part, supported by the U.S. Department of Energy at LLNL under Contact No.W7405-Eng-48 Table 1
Chemical Compositions of SiC Particle and 6061 Aluminium Alloy crystal SiC SiO2 Si C A1 Density ds0 phase (g/cm3) (lam) SiC ct 94.0 1.30 1.53 1.05 0.02 3.14 0.6 Si
6061
Cu
0.71 0.36
Zn
Mg
Cr
Ti
AI
0.18
0.01
0.75
0.02
Bal
also:Averageparticlesize(lam)
Fig. 1 SEM microstructures of the SiCp/6061 A1 composite (a) hot-rolled and extruded after vortex method & squeeze casting and (b) fabricated by squeeze casting after vortex method
Vol. 31, No. 9
SUPERPLASTICITYCOMPOSITE
1185
100 SiCp/6061 AI composite, Vf=0.20 Vortex method, squeeze casting, extr tsion & hot rolling i Rolling temp.=798K
m=0.33 10
f
._O____3~._.._-----e
0
1
Testing temp.
. . . . . . . . .
.01
'
' , ,,,,1
.1
,
.......
1
10
Strain rate(llsec) Fig. 2 Relationship between flow stress and strain rate of the SiCp/6061 aluminium alloy composite hot-rolled and extruded after vortex & squeeze castings 1000 :Vortex method, squeeze casting, extrusion &~-;::~:::==..-=..:. -hot rolling . . . . . . . ~ - - . . . . . . . . . . . . . ~,-Rolling t e m p . = 7 9 8 K . . . . . . . . . . . . . . . . . . . . . ~---........................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
o
S
o . ......o o ; [
1 O0 ~ ' : : : = . : ' :
~:::::::::::::::::
:..0.::::::~@?iii::33333S::333337::.:.337iii each passes(mm) _.__
o
..........................................................i .........................................................[
E10
.01
.
.
.
.
.
.
.
.
'
.
.1
.
.
.
.
.
.
.
t°
1
:0.5mm
]
..............
10
Strain rate(llsec) Fig. 3 Relationship between total elongation and strain rate of the SiCp/6061 AI alloy composite hot-rolled and extruded after vortex & squeeze castings
Fig.4
(a) E --0.27S -1, the total elongation=207%, (b) Before test Superplastic deformed sample of the SIC/6061 A1 composite fabricated by vortex method before squeeze casting, extrusion and hot rolling
1186
SUPERPLASTICITY COMPOSITE
15
,-~
10
Vol. 31, No. 9
SiCpl6061 Al'composite [ O , ~,,,,~, II . . . . t : x . ~ , . ~ J t ~Jt i o ) II Vl=,.z, [ • :0.735(11S) 1~ t [ Ill "0 273(11S) I/ 0 0 0,-,~ _J A [0:133(11S) t] ................................ x . . , " ~ ........................... rn :0.083(11S)
]C 0
] •
:0.014(11S)ii
....................................... t
ol-0.0
0.5
1.0
J 1.5
T r u e strain Fig. 5
Flow stress-true strain curves of the SiCp/6061 A1 composite fabricated by vortex & squeeze castings before extrusion and hot rolling
Fig.6 Fracture surface of the SiCp/6061 aluminium alloy composite hot-rolled and extruded after vortex & squeeze castings
Scripta Metallurgica
et
Materialia, Vol. 31, No. 9, pp. 1181-1186, 1994 Copyright © 1994 Elsevier Science Ltd Printed in the USA. All rights reserved 0956-716X/94 $6.00 + 00
HIGH STRAIN RATE SUPERPLASTICITY OF A SiC PARTICULATE REINFORCED ALUMINIUM ALLOY COMPOSITE BY A VORTEX METHOD Takeo Hikosaka*, Tsunemichi Imai**, T.G.Nieh **and Jeff Wadsworth*** * Industrial Research Institute, Aichi Prefectural Government, Nishishinwari Hitotsuki, Kariya City, Aichi 448, Japan ** National Industrial Research Institute of Nagoya, 1 Hirate-cho, Kita-ku, Nagoya 462, Japan *** Lawrence Livermore National Laboratory, P.O.Box 808, Livermore, CA 94551-9900, U.S.A. (Received May 3, 1994) (Revised June 13, 1994)
Introduction High strain rate superplasticity (HSRS) for ceramic whisker or particulate reinforced aluminium alloy composites exhibiting a total elongation of 250-600% at a high strain rate such as 0.1-10S -l is expected to establish an efficient, near-net shape forming for automobile engineering components, aerospace structures and semi-conductor packagings (111). The composites can be fabricated by squeeze casting, the vortex method and compocasting, the powder metallurgical (P/M) method and spray deposition. Casting processes such as squeeze casting, compocasting and the vortex method are cost-effective. The composites fabricated by casting processes have already been applied to automobile engine components, satellite components and the like (12). Cast aluminium alloy composites have serious problems for practical application in that their tensile ductility and fracture toughness at room temperature are significantly poor and their relatively large ceramic particles make them too hard. These problems encourage the establishment of a secondary fabrication process which can efficiently produce engineering components of a cast aluminium alloy composite. The ceramic particulates reinforced aluminium alloy composites which can produce HSRS have been fabricated primarily by a P/M method. However, the superplastic aluminium alloy P/M composites are too expensive for use in non-military engineering components (1). A vortex method has been used to produce a metal matrix composite in which agglomerated particles and several defects result in poor quality. Thus, it is important to improve fabrication processing in order to make fine ceramic particles dispersed homogeneously and to remove defects in the composite. The purpose of this study is to establish thermomechanical processing to build fine microstructure and to produce HSRS for a SiC particulate reinforced aluminium alloy composite fabricated by a voltex method and to make clear the superplastic characteristics. 1181
1182
SUPERPLASTICITY COMPOSITE
Vol. 31, No. 9
Experimental Procedure SiC particles (the average particle size of dso=0.61am) were used as reinforcement materials. Table 1 shows the chemical compositions of the SiC particles and 6061 aluminium alloy. The molten 6061 aluminium alloy heated at 1023K was stirred with the heating SiC particles and 0.3%wt-calcium at a rotating speed of 500-700rpm in a crucible for 90 minutes by vortex method equipment. The volume fraction of the SiC particle was about Vf=0.20. The as-cast composite was reforged at 1123K in an atmosphere under the pressure of 100MPa by a squeeze casting machine. The mold was heated at 623K. Thermomechanical processings used to produce HSRS for the composite was hot rolling after extrusion. Hot extrusion was performed with the extrusion ratio of 56 at 623K. After heating at 798K, the composite was hot-rolled. The thickness reduction of each rolling pass was 0.5mm and the reheating-holding time between rolling passes was about 5 minutes. The final thickness of the composite hot-rolled was about 0.75mm. Tensile specimens with a 4mm gage width and a 5.5mm gage length were pulled at 853K and in the strain rate region from 0.01 to about 2S--1. The microstructure and fracture surface were observed by TEM and SEM. Experimental Results and Discussion Figures 1 show optical microstructures of the SiCp/6061 aluminium alloy composites (a) squeeze casting after a vortex method and (b) hot-rolled after a vortex method, squeeze casting and extrusion, respectively. SiC particle size was dispersed homogeneously in the SiCp/6061 AI composite hot-rolled after the vortex method, squeeze casting and extrusion although an aluminium alloy layer and some agglomerated SiC particles appear in the asextruded composite. A relationship between a flow stress (or) and a true strain rate (e) in superplastic materials can be expressed as the equation o=Ke ~, where K is a constant. It is necessary to find optimum testing temperature and optimum strain rate in which the strain rate sensitivity of a flow stress, m-value, is larger than 0.3 because a higher m value suppresses the development of necking and leads to higher total elongation. Figure 2 shows the relationship between the flow stress and the strain rate of the SiCp/6061 aluminum alloy composite fabricated by the vortex method before squeeze casting, extrusion and hot rolling. The flow stress in the composite increases linearly with a raising strain rate and the strain rate sensitivity of the flow stress (the m value) shows about 0.33 in the strain rate region from 0.1S -~ up to 1.3S-1 and at 833K, but the m value becomes less than 0.3 in the strain rate less than 1.0S-1 . Total elongation of the composite is shown in Fig. 3. The superplastically deformed SiCp/6061 AI composite in which maximum total elongation of about 200% was obtained is shown in Fig.4. The total elongation of the SiCp/6061 AI composite became about 200% in the strain rate region from 0.1S ~ to 0.3S -I and the total elongation more than 100% was obtained in the wide strain rate region from 0.01S ~up to 0.gs -j . The result indicates that defects in the SIC/6061 aluminium alloy composite fabricated by the vortex method can be removed by squeeze casting, and hot rolling after extrusion has a significant effect on making finer SiC particles dispersed homogeneously.
Vol. 31, No. 9
SUPERPLASTICITY COMPOSITE
1183
The superplastic deformation mechanism includes fine grain boundary sliding, interfacial sliding at a liquid phase and dynamic recrystallization. The m value of 0.33 in Fig.2 shows that the SiCp/6061 A1 composites could produce HSRS predominantly by fine grain boundary sliding. Figure 5 shows the flow stress-true strain curves of the SiCp/6061 AI composite fabricated by the vortex method and squeeze casting before extrusion and hot rolling. The maximum flow stress increases with a raising strain rate and, strain hardening and softening in these flow stress-true strain curves are not so high; therefore, continuous recrystallization of the SIC/6061 A1 composite may be accomplished during hot rolling and extrusion. A fracture surface of the SiCp/6061 AI composites hot-rolled after extrusion, the vortex method and squeeze casting is shown in Fig. 6. The strain rate and the total elongation of the composite are 0.13S -1 and about 200%, respectively. The fracture surface of the composite has a partially melted matrix although the composite was deformed just below the solidus temperature of the 6061 aluminium matrix, and filaments appear on the fracture surface. The diameter of the filaments in the SiCp/6061 AI composite is very fine due to the finer relative distance between SiC particles. The filament should be related to a semi-liquid phase at or near a SiCp/6061 interface since the semi-liquid layer at the interface between the matrix and the SiC particle could be elongated significantly during hot rolling and superplastic deformation. The Mg segregation in the SiCp/6061 AI composite should occur because the SIC/6061 AI composite was deformed with a matrix and at the interface in a partially liquid phase condition (9, 10). The SiCp/6061 AI composite can achieve the high total elongation of about 200% by interfacial sliding at a liquid phase in addition to fine grain boundary sliding. Conclusions SiCp/6061 AI alloy composites fabricated by a vortex method and squeeze casting were hot-rolled after extrusion and the superplastic chracteristics of the composite were investigated. The following results were obtained: (l)The strain rate sensitivity (m value) of the SiCp/6061 AI composites is 0.33. (2)The SiCp/6061 AI composite hot-rolled and extruded after the vortex mehtod and squeeze casting exhibited the total elongation of 200% in strain rates from 0.13S -1 to 0.3 S-1 at 853K. (3)The fracture surface of the composite has a partially liquid phase although the composite was deformed just below the solidus temperature of the 6061 matrix and filaments appeared, lnterfacial sliding at the liquid phase contributes to HSRS in addition to fine grain boundary sliding. References 1. T.G.Nieh, C.A.Henshall and J.Wadsworth, Scripta Metallurgica, 18-12(1984) 1405/1408 2. M.W.Mahoney and A.K.Ghosh, Metall. Trans, 18A(1987) 653/661 3. T.Imai, M.Mabuchi, Y.Tozawa and M.Yamada,J.Materials Science letters, 9(1990) 255/257 4. M.Mabuchi, T.Imai, K.Kubo, H.Higashi, Y.Obada and T.Tanimura, Materials Letters,11,12(1991)339/342
1184
SUPERPLASTICITY COMPOSITE
Vol. 31, No. 9
5.
M.Mabuchi, K.Higashi, Y.Okada, S.Tanimura, T.Imai and K.Kubo,Scripta Metallurgica et Materialia, 25(1991)2517/2522 6. T.Imai, M.Mabuchi and T.Tozawa, Superplasticity in Advanced Materials, edited by S.Hori,M.Tokizane and N.Furushiro(A Publication of JSRS, 1991)373/378 7. T.Tsuzuki and A.Takahashi, Proc. of 1st Japan International SAMPE Symposium (Nov.28-Decl, 1989)243 8. T.G.Nieh and J.Wadsworth, Superplasticity in Advanced Materials, edited by S.Hori, M.Tokizane and N.Furushiro(A Publication of JSRS, 1991)339/348 9. G.L'Esperance, T.Imai and B.Hong, ibid, 379/384 10. T.Imai, G.L'Esperance, B.Hong, M.Mabuchi, and Y.Tozawa, Advances in Powder Metallurgy & Particulate Materials-1992, compiled by J.M.Caus and R.M.German, 9(1992) 181/194 11. T.lmai, G.L'Esperance & B.D.Hong, Scripta Metall.et Mate., accepted 12. S.Kennerknecht, Fabrication of Particulate Reinforced Metal Composites, edited by J.Masounave & F.G.Hamel, (1990, published by ASM International)87/100 Acknowledgment The financial support of the New Enegy and Industrial Technology Development Organization (NEDO) of Japan is greatly acknowledged. And this work was, in part, supported by the U.S. Department of Energy at LLNL under Contact No.W7405-Eng-48 Table 1
Chemical Compositions of SiC Particle and 6061 Aluminium Alloy crystal SiC SiO2 Si C A1 Density ds0 phase (g/cm3) (lam) SiC ct 94.0 1.30 1.53 1.05 0.02 3.14 0.6 Si
6061
Cu
0.71 0.36
Zn
Mg
Cr
Ti
AI
0.18
0.01
0.75
0.02
Bal
also:Averageparticlesize(lam)
Fig. 1 SEM microstructures of the SiCp/6061 A1 composite (a) hot-rolled and extruded after vortex method & squeeze casting and (b) fabricated by squeeze casting after vortex method
Vol. 31, No. 9
SUPERPLASTICITYCOMPOSITE
1185
100 SiCp/6061 AI composite, Vf=0.20 Vortex method, squeeze casting, extr tsion & hot rolling i Rolling temp.=798K
m=0.33 10
f
._O____3~._.._-----e
0
1
Testing temp.
. . . . . . . . .
.01
'
' , ,,,,1
.1
,
.......
1
10
Strain rate(llsec) Fig. 2 Relationship between flow stress and strain rate of the SiCp/6061 aluminium alloy composite hot-rolled and extruded after vortex & squeeze castings 1000 :Vortex method, squeeze casting, extrusion &~-;::~:::==..-=..:. -hot rolling . . . . . . . ~ - - . . . . . . . . . . . . . ~,-Rolling t e m p . = 7 9 8 K . . . . . . . . . . . . . . . . . . . . . ~---........................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
o
S
o . ......o o ; [
1 O0 ~ ' : : : = . : ' :
~:::::::::::::::::
:..0.::::::~@?iii::33333S::333337::.:.337iii each passes(mm) _.__
o
..........................................................i .........................................................[
E10
.01
.
.
.
.
.
.
.
.
'
.
.1
.
.
.
.
.
.
.
t°
1
:0.5mm
]
..............
10
Strain rate(llsec) Fig. 3 Relationship between total elongation and strain rate of the SiCp/6061 AI alloy composite hot-rolled and extruded after vortex & squeeze castings
Fig.4
(a) E --0.27S -1, the total elongation=207%, (b) Before test Superplastic deformed sample of the SIC/6061 A1 composite fabricated by vortex method before squeeze casting, extrusion and hot rolling
1186
SUPERPLASTICITY COMPOSITE
15
,-~
10
Vol. 31, No. 9
SiCpl6061 Al'composite [ O , ~,,,,~, II . . . . t : x . ~ , . ~ J t ~Jt i o ) II Vl=,.z, [ • :0.735(11S) 1~ t [ Ill "0 273(11S) I/ 0 0 0,-,~ _J A [0:133(11S) t] ................................ x . . , " ~ ........................... rn :0.083(11S)
]C 0
] •
:0.014(11S)ii
....................................... t
ol-0.0
0.5
1.0
J 1.5
T r u e strain Fig. 5
Flow stress-true strain curves of the SiCp/6061 A1 composite fabricated by vortex & squeeze castings before extrusion and hot rolling
Fig.6 Fracture surface of the SiCp/6061 aluminium alloy composite hot-rolled and extruded after vortex & squeeze castings