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High temperature mechanical properties of a β-Si3N4 whisker reinforced aluminium alloy composite produced by squeeze casting
ScriptaMetallurgic8et Mdcriali
Vol. 32, No. 11,
Pergamon 0!356-716X(!B)OOO10-0
HIGH TEMPERATURE MECHANICAL PROPERTIES OF A p-S&N4WHISKER REINFORCED ALUMINIUM ALLOY COMPOSITE PRODUCED BY SQUEEZE CASTING Isao To&@*, Tsunemichi Imai** and Kyosuke Ai*** *Kanagawa High-Technology Foundation, Kanagawa Science Park 3-2- 1, Sakato Takatsu-ku, Kawasaki 2 13, Japan **National Industrial Research Insitutte of Nagoya, 1 Hirate-cho, Kita-ku, Nagoya 462 Japan ***Industrial Research Institute of Kanagawa, 3 173 Showa-Machi, Kanazawa-ku, Yokohama 236, Japan (Received November 11,1994) (Revised December 20,1994)
Ceramic whisker reinforced aluminium alloy composites exhibit higher specific tensile strength and specific elastic moduli, excellent wear resistance and heat reisistance, low thermal expansion. As a results, they have apotentialforuseinaerospacestmcmms, automobile engineering components, semiconducter packgings and so on. The composites can be fabricated by a P/M method, squeeze casting, compocasting and spray deposition. The squeeze casting has been already established as a practical near-net shape forming method for the composite engine components with a complicated shape such as a piston, a connecting rod, a cylinder linear, etc. Recently, it was found that altium alloy composites reinforced by Sic or S&N, whiskers or particulates can exhibit superplasticity at a very high strain rate such as 0. 1- 10 s-r (HSRS). However, up to date, it was mported that the HSRS composites coukl be fabricated by the P/M method tLV7]. It is thought that metal matrix composites fabricated by the P/M route is too expensive to apply to a non-military field such as automobile engineering components. It is, therefore, important to produce HSRS for composite materials fabricated by cost-effective processing such as squeeze casting in order to establish practical near-net shape superplastic forming and forging. Tsuzuku and Takahashi reported superplastic forging of a SiCwnO75 aluminium alloy composite fabricated by squeeze casting before extrusion and hot rolling by which the superplasticty at the strain rate of about 0.02 s? [email protected] et al reported that a SiCw/2324 Al composite extruded atler squeeze casting exhibites the total elongation of about 500 % at the strain rate of 0.02 S’ t9]. However, it has not yet been reported if a S-Si& whisker minfomed ahnninium alloy composite fabricated by squeeze casting can produce HSRS. It is, therefore, necessary to establish the optimum thermomechanical processing to produce HSRS for a composite fabricated by squeeze casting. The aim ofthis study is to investigate the tensile strength at an elevated temperature and the superplastic 1801
1802
MECHANICAL PROPERTIES OF A SQUEEZE CAST ALLOY
Vol. 32, No. 11
&am&r&z ofa p&N, whisker reinforced ahrminium alloy composite fabricated by squeeze casting and the superplastic deformation mechanism of the composite. Procedureg materials used were p-S&N, whiskers which had a diameter of about 1pm and the length of 10-20 pm and the whiskem were fabricated by a water absorbed method. The molten 606 1 ahuninium alloy was intiltrated into the p -Si$J, whisker prefm by the pressure of about 1000 Pa under the mold kept at 823 K r&r the molten 606 1 ahtminium ahoy and the preform were heated up to 1073 K. The composite was exuuded with the extrusion ratios of 44 and 100 at 773 K. The tensile specimen with a gage diameter of 3 mm and a gage length of 10 mm was pulled at 8 18 K. The testing strain rates were changed from 0.01 to about 2 s-l, A tensile test to evaluate the tensile strength was performed up to at 673 K and at 0.001 s‘l. The microstructure and the fracture surface were observed by SE&l and EM. Thex-eirbxcement
Microstructuq The volume fi-actions (Vt) of the p-S&N, whisker preform which originally had Vf = 0.20 was compressed during inflitration of a molten aluminium alloy so as to result in about Vf = 0.25. Although the S-S&N, whiskers of the composite fabricated by the squeeze casting were randomly arranged, the whiskers were oriented to an extrusion direction after extrusion as shown in Fig. 1. As squeeze casting can fabricate the eng&e&g componems in a few minutes, a contact time between ceramic whiskers and a molten alummium alloy was so short as to build a clean interface between the matrix and reinforcement material without a reaction product. On the surface of the whisker etched deeply after squeeze casting, no seriously reaction product was detected except AlN which indicates that the interface was clean. Tensile strewth The squeeze casting has the benefit of not damaging a whisker so that it is thought that the metal matrix composite (MMC) produced by squeeze casting contains longer whiskers than that produced by the P/M method. Fig. 2 shows the tensile strength at an elevated temperature of the @Si,N,/6061 Al composite, the as-cast a-Si,N,w/6Q61 Al composite and the as-cast 606 1 matrix. The tensile strengths of the p -Si,N,/606 1 Al composite become about 400 MPa at mom temperature and about 250 MPa at 573 K which is higher than those of the as-cast a -Si,N,w/606 1 Al composite and the as-cast 606 1 matrix. The results indicate that a S-E&N,whisker has a stronga e&t on a tensile strength of an aluminium alloy composite than that observed in an a -Si,N,w/606 1 Al composite.
Sunerulastic characteristics
The compo&e fabricated by squeeze casting con&s just of the 606 1 aluminium alloy and p -Si,N, whisk-em, although in the composite fabricated by the PA4 method, alumina and magnesia particles are dispersed in the matrix in addtion to S-S&N, whiskers because a surface of a 606 1 ahrminium alloy powder is covered by ahrminaor magnesia t’o! These particles and the whisker can work jointly as obstacles for grain growth during hot deformation. However, squeeze casting is superior to produce action of a reinforcement material on the superplastic characteristics of the ceramic whisker and aluminium alloy system composites to the P/M method. Figure 3 indicates the relationship between a flow stress and a strain rate of the SSi,N,w/6061 Al composite fabricated by squeeze casting before hot extrusion as compared with those produced by the P/M route. The P/M route includes hot pressing and hot extrusion. The flow stress of the composite extruded atIer
Vol. 32, No. 11
MECHANICAL
PROPERTIES
OF A SQUEEZE CAST ALLOY
1803
squeeze casting is higher than that of the composite extruded in the PM route with the same extrusion ratio. The primax@reason is that the volume fraction of the whiskers of Vf = 0.25 produced by squeeze casting is higher than that produced by the P/M route. The strain rate sensitivity of the flow stress (m value) in the composite pmduced by the squeeze casting is 0.3, although the m value of the composite produced by the P/M route becomes about 0.46. A constitutive equation for superplastic materials is expressed as o = K?“, where o is the flow stress, t ~strainrate,Kaconstantandmthr:strainratesensistivityoftheflowstress. Themvahteislargerthan0.3 for a superplastic ahnninium alloy,inwhichtine grainboundaty sliding is a primarily deformation mechanism, because the higher m value avoids necking and leads to higher total elongation. The result of Fig. 3 indicates that the superplastic deformation mechanism of both composites which have the m value larger than 0.3 consists of line grain boundary sliding. Figure 4 shows the relationship between a total elongation and a strain rate of the as-extruded g-S&N, w/606 1 Al composites fabricated by the squeeze casting and by the P/M route, and tensile specimens prior to tensile tests and after superplastic deformation are shown in Figure 5. The g-Si,N,w/6061 Al composite by squeeze casting had about 173 % at the strain rate of 0.02 s”, although the g-Si,N,w/6061 Al composite The fabricated by the P/M route exhibites the total elongation of 600 % at the strain rate of about 0.2 s* t4s61. result repmsents that ceramic whiskers reinforced ahnninium alloy composites produced by squeese casting could produce excellent high strain rate superplasticity. Fracture
surface
Defamation mechanisms of HSRS for MMC include dynamic recrystalization and interfacial sliding [“l in additionto& grain boundary sliding because MMC has a lot of interfaces and the deformation mechanism should be diff&ent from that of a conventional superplastic ahuninum alloy. Figure 6 indicates a fiactrue surface of the g -Si,N,w/606 1 Al composite fabricated by squeeze casting before extrusion Although the composite was pulled just below the solidus temperature of the 6061 aluminum alloy, the f+actrue surface includes a partially melt matrix and also small filaments appear. L’Esperance et al demonstrated that in g -Si,N4w/2 124 Al ~1 and S -Si,N4w/7064 Al compsoites [I31the segregation of Mg and Cu was detected at the interfaces between the whisker and matrix. Since the segr;gation of Mg and Cu could reduce the melting tempaature of the ahtminium solid so&ion at the inte&ce and produce an interfacial sliding, it is thought that interfacial sliding at a requid phase should promote HSRS in addition to fine grain boundary sliding for the l.3-Si,N,w/606 1 Al composite fabricated by squeeze casting. Conclusions
The g-Si$14w/6061Al composite was fabricated by the squeeze casting and extruded with the extrusion ratios of 44 and 100 at 773 K. Its tensile strength and superplastic characteristics were investigated and the following results were obtained. (1) The p-S&N4w/6061AI composite exhibites the tensilestrengths of about 400 MPa at room temperature and of about 250 MPa at 773 K. (2) The m value of the composite pulled at 818 K is 0.33 in the strain rate range from 0.02 up to 1.0 s-l. (3) The total elongation of the composite becomes about 173 % at the strain rate of 0.02 s-l even in the case of the high volume fraction of 0.25. (4) No reaction product on the surface of g-Si& whisker after removing a matrix by etching was detected except AlN. (5) ‘Ihe fiactrue surface of the composite includes the melt matrix and small filaments, which shows that interfacial sliding should promot HSRS in addition to fine grain boundary sliding.
1804
Vol. 32, No. 11
MECHANICAL PROPERTIES OF A SQUEEZE CAST ALLOY
References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
T.G. Nieb, CA. Hen&all and J. Wadsworth, Scripta Metallurgica, 18-12 (1984) 1405 1408 M.W. Mahoney and AK w ~etall. crank, 18~ (1987) 653661 T. Iok. M.Mabuchi. Y. Tozawa end M. Yamada, JMateriak Science letters,9 (1990) 255-257 Mat&& L&s, 10 (1991) 339342 M.Malkhi,T.Ln~ai,K.Kubo,H.HiSashi,Y.Ol&aaadT.Ti~imua, T. Imai, G.L’Esperancxand B.D. Hong, ScriptaMetaU.etMater., 31-9 (1994) 1181-l 186 M. M&&i, K. H&&i, Y. C&da, S. Tanimum, T. Imai and K. Kubo, Scripta Metallurgica et Matek& 25 (1991) 2517-2522 T. Imai,M. Mabucbi and T. Tozawa, Superplesticityin advanced materialsedited by S. Hori, M. Tokizene and N. Fuusbiro (A Publication of JSRS, 1991) 373-378 T. Tsuzuki end A Takaha& Pmt. of 1st Japan Inkmational SAMPE Symposium (Nov. 28&c. 1,1989) 243 M.Kon, J. Kaneko and S. Sugamata, J the Japan Society for Tecbno~ogy of Plasticity, 35-402 (1994) 823-828 RAShabeni and T.W.Clyne, Materials Science & EnginecrinS,Al35 (1991) 281-285 T.G. Nieh and J. Wadsworth, Superplasticity in Advanced Materials edii by S. Hori, M. Tokkane and N. Furushiro (A Publication ofJSRS, 1991), 339-348 G. LZqemnce, T. Imai and B.Hong. ibid, 379-384 T. Imai, G.L ‘Esperance,B. Hong. M. Mabuchi, and Y. Tozawa, Advances io Powder Metallurgy & ParticulateMaterials-1992 compiled by J.M. Caus aad RM. German, 9 (1992) 181-194
Figure 1. Mirrostructureof (a) the as-cast and @) es-extnukd p-Si,N,w/6061 Al composiks.
loo-
10
Temperature Figure 2. The tensile strengthsofthe as-e-
/K
$-Si,N,w/ 6061 Al, as-cast a-Si,N,w/6061 AL
MECHANICAL
Vol. 32. No. 11
o!al
PROPERTIES
L
II
0.1
0.01
Strain Figure 3. The relationship ratios of 44 and 100.
1805
OF A SQUEEZE CAST ALLQY
I/S’
rate
between the flow stress and the strain rate of the @Si,N,w/6061
Al composite extruded with the extmsion
l-
l:Si~NdJ6051.Rl(Xts/q x
i
UX-P/Mj
A
A .A
0
/ A
=.
+ 0
0
Figure 4. Tlx relatioosbip between tbe total elmgatim and the strain rate of the j%Si,N,w/606 1 Al composite extruded with the extrusion ratios of44 and 100.
(a)Before test
(b) i: = 0.21 s-1 ( T= 818 K
Figure 5. Superplastic defomxl
sample ofthe (bSi,N,w/6061
Al wmposb.
1806
MECHANICAL. PROPERTIES
OF A SQUEEZE CAST ALLOY
Figure 6. Fracture surface ofthe p-Si,N,w/6061
Al composite pulled at the strain rate of 0.21 d.
Vol. 32, No. 11
Vol. 32, No. 11,
Pergamon 0!356-716X(!B)OOO10-0
HIGH TEMPERATURE MECHANICAL PROPERTIES OF A p-S&N4WHISKER REINFORCED ALUMINIUM ALLOY COMPOSITE PRODUCED BY SQUEEZE CASTING Isao To&@*, Tsunemichi Imai** and Kyosuke Ai*** *Kanagawa High-Technology Foundation, Kanagawa Science Park 3-2- 1, Sakato Takatsu-ku, Kawasaki 2 13, Japan **National Industrial Research Insitutte of Nagoya, 1 Hirate-cho, Kita-ku, Nagoya 462 Japan ***Industrial Research Institute of Kanagawa, 3 173 Showa-Machi, Kanazawa-ku, Yokohama 236, Japan (Received November 11,1994) (Revised December 20,1994)
Ceramic whisker reinforced aluminium alloy composites exhibit higher specific tensile strength and specific elastic moduli, excellent wear resistance and heat reisistance, low thermal expansion. As a results, they have apotentialforuseinaerospacestmcmms, automobile engineering components, semiconducter packgings and so on. The composites can be fabricated by a P/M method, squeeze casting, compocasting and spray deposition. The squeeze casting has been already established as a practical near-net shape forming method for the composite engine components with a complicated shape such as a piston, a connecting rod, a cylinder linear, etc. Recently, it was found that altium alloy composites reinforced by Sic or S&N, whiskers or particulates can exhibit superplasticity at a very high strain rate such as 0. 1- 10 s-r (HSRS). However, up to date, it was mported that the HSRS composites coukl be fabricated by the P/M method tLV7]. It is thought that metal matrix composites fabricated by the P/M route is too expensive to apply to a non-military field such as automobile engineering components. It is, therefore, important to produce HSRS for composite materials fabricated by cost-effective processing such as squeeze casting in order to establish practical near-net shape superplastic forming and forging. Tsuzuku and Takahashi reported superplastic forging of a SiCwnO75 aluminium alloy composite fabricated by squeeze casting before extrusion and hot rolling by which the superplasticty at the strain rate of about 0.02 s? [email protected] et al reported that a SiCw/2324 Al composite extruded atler squeeze casting exhibites the total elongation of about 500 % at the strain rate of 0.02 S’ t9]. However, it has not yet been reported if a S-Si& whisker minfomed ahnninium alloy composite fabricated by squeeze casting can produce HSRS. It is, therefore, necessary to establish the optimum thermomechanical processing to produce HSRS for a composite fabricated by squeeze casting. The aim ofthis study is to investigate the tensile strength at an elevated temperature and the superplastic 1801
1802
MECHANICAL PROPERTIES OF A SQUEEZE CAST ALLOY
Vol. 32, No. 11
&am&r&z ofa p&N, whisker reinforced ahrminium alloy composite fabricated by squeeze casting and the superplastic deformation mechanism of the composite. Procedureg materials used were p-S&N, whiskers which had a diameter of about 1pm and the length of 10-20 pm and the whiskem were fabricated by a water absorbed method. The molten 606 1 ahuninium alloy was intiltrated into the p -Si$J, whisker prefm by the pressure of about 1000 Pa under the mold kept at 823 K r&r the molten 606 1 ahtminium ahoy and the preform were heated up to 1073 K. The composite was exuuded with the extrusion ratios of 44 and 100 at 773 K. The tensile specimen with a gage diameter of 3 mm and a gage length of 10 mm was pulled at 8 18 K. The testing strain rates were changed from 0.01 to about 2 s-l, A tensile test to evaluate the tensile strength was performed up to at 673 K and at 0.001 s‘l. The microstructure and the fracture surface were observed by SE&l and EM. Thex-eirbxcement
Microstructuq The volume fi-actions (Vt) of the p-S&N, whisker preform which originally had Vf = 0.20 was compressed during inflitration of a molten aluminium alloy so as to result in about Vf = 0.25. Although the S-S&N, whiskers of the composite fabricated by the squeeze casting were randomly arranged, the whiskers were oriented to an extrusion direction after extrusion as shown in Fig. 1. As squeeze casting can fabricate the eng&e&g componems in a few minutes, a contact time between ceramic whiskers and a molten alummium alloy was so short as to build a clean interface between the matrix and reinforcement material without a reaction product. On the surface of the whisker etched deeply after squeeze casting, no seriously reaction product was detected except AlN which indicates that the interface was clean. Tensile strewth The squeeze casting has the benefit of not damaging a whisker so that it is thought that the metal matrix composite (MMC) produced by squeeze casting contains longer whiskers than that produced by the P/M method. Fig. 2 shows the tensile strength at an elevated temperature of the @Si,N,/6061 Al composite, the as-cast a-Si,N,w/6Q61 Al composite and the as-cast 606 1 matrix. The tensile strengths of the p -Si,N,/606 1 Al composite become about 400 MPa at mom temperature and about 250 MPa at 573 K which is higher than those of the as-cast a -Si,N,w/606 1 Al composite and the as-cast 606 1 matrix. The results indicate that a S-E&N,whisker has a stronga e&t on a tensile strength of an aluminium alloy composite than that observed in an a -Si,N,w/606 1 Al composite.
Sunerulastic characteristics
The compo&e fabricated by squeeze casting con&s just of the 606 1 aluminium alloy and p -Si,N, whisk-em, although in the composite fabricated by the PA4 method, alumina and magnesia particles are dispersed in the matrix in addtion to S-S&N, whiskers because a surface of a 606 1 ahrminium alloy powder is covered by ahrminaor magnesia t’o! These particles and the whisker can work jointly as obstacles for grain growth during hot deformation. However, squeeze casting is superior to produce action of a reinforcement material on the superplastic characteristics of the ceramic whisker and aluminium alloy system composites to the P/M method. Figure 3 indicates the relationship between a flow stress and a strain rate of the SSi,N,w/6061 Al composite fabricated by squeeze casting before hot extrusion as compared with those produced by the P/M route. The P/M route includes hot pressing and hot extrusion. The flow stress of the composite extruded atIer
Vol. 32, No. 11
MECHANICAL
PROPERTIES
OF A SQUEEZE CAST ALLOY
1803
squeeze casting is higher than that of the composite extruded in the PM route with the same extrusion ratio. The primax@reason is that the volume fraction of the whiskers of Vf = 0.25 produced by squeeze casting is higher than that produced by the P/M route. The strain rate sensitivity of the flow stress (m value) in the composite pmduced by the squeeze casting is 0.3, although the m value of the composite produced by the P/M route becomes about 0.46. A constitutive equation for superplastic materials is expressed as o = K?“, where o is the flow stress, t ~strainrate,Kaconstantandmthr:strainratesensistivityoftheflowstress. Themvahteislargerthan0.3 for a superplastic ahnninium alloy,inwhichtine grainboundaty sliding is a primarily deformation mechanism, because the higher m value avoids necking and leads to higher total elongation. The result of Fig. 3 indicates that the superplastic deformation mechanism of both composites which have the m value larger than 0.3 consists of line grain boundary sliding. Figure 4 shows the relationship between a total elongation and a strain rate of the as-extruded g-S&N, w/606 1 Al composites fabricated by the squeeze casting and by the P/M route, and tensile specimens prior to tensile tests and after superplastic deformation are shown in Figure 5. The g-Si,N,w/6061 Al composite by squeeze casting had about 173 % at the strain rate of 0.02 s”, although the g-Si,N,w/6061 Al composite The fabricated by the P/M route exhibites the total elongation of 600 % at the strain rate of about 0.2 s* t4s61. result repmsents that ceramic whiskers reinforced ahnninium alloy composites produced by squeese casting could produce excellent high strain rate superplasticity. Fracture
surface
Defamation mechanisms of HSRS for MMC include dynamic recrystalization and interfacial sliding [“l in additionto& grain boundary sliding because MMC has a lot of interfaces and the deformation mechanism should be diff&ent from that of a conventional superplastic ahuninum alloy. Figure 6 indicates a fiactrue surface of the g -Si,N,w/606 1 Al composite fabricated by squeeze casting before extrusion Although the composite was pulled just below the solidus temperature of the 6061 aluminum alloy, the f+actrue surface includes a partially melt matrix and also small filaments appear. L’Esperance et al demonstrated that in g -Si,N4w/2 124 Al ~1 and S -Si,N4w/7064 Al compsoites [I31the segregation of Mg and Cu was detected at the interfaces between the whisker and matrix. Since the segr;gation of Mg and Cu could reduce the melting tempaature of the ahtminium solid so&ion at the inte&ce and produce an interfacial sliding, it is thought that interfacial sliding at a requid phase should promote HSRS in addition to fine grain boundary sliding for the l.3-Si,N,w/606 1 Al composite fabricated by squeeze casting. Conclusions
The g-Si$14w/6061Al composite was fabricated by the squeeze casting and extruded with the extrusion ratios of 44 and 100 at 773 K. Its tensile strength and superplastic characteristics were investigated and the following results were obtained. (1) The p-S&N4w/6061AI composite exhibites the tensilestrengths of about 400 MPa at room temperature and of about 250 MPa at 773 K. (2) The m value of the composite pulled at 818 K is 0.33 in the strain rate range from 0.02 up to 1.0 s-l. (3) The total elongation of the composite becomes about 173 % at the strain rate of 0.02 s-l even in the case of the high volume fraction of 0.25. (4) No reaction product on the surface of g-Si& whisker after removing a matrix by etching was detected except AlN. (5) ‘Ihe fiactrue surface of the composite includes the melt matrix and small filaments, which shows that interfacial sliding should promot HSRS in addition to fine grain boundary sliding.
1804
Vol. 32, No. 11
MECHANICAL PROPERTIES OF A SQUEEZE CAST ALLOY
References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
T.G. Nieb, CA. Hen&all and J. Wadsworth, Scripta Metallurgica, 18-12 (1984) 1405 1408 M.W. Mahoney and AK w ~etall. crank, 18~ (1987) 653661 T. Iok. M.Mabuchi. Y. Tozawa end M. Yamada, JMateriak Science letters,9 (1990) 255-257 Mat&& L&s, 10 (1991) 339342 M.Malkhi,T.Ln~ai,K.Kubo,H.HiSashi,Y.Ol&aaadT.Ti~imua, T. Imai, G.L’Esperancxand B.D. Hong, ScriptaMetaU.etMater., 31-9 (1994) 1181-l 186 M. M&&i, K. H&&i, Y. C&da, S. Tanimum, T. Imai and K. Kubo, Scripta Metallurgica et Matek& 25 (1991) 2517-2522 T. Imai,M. Mabucbi and T. Tozawa, Superplesticityin advanced materialsedited by S. Hori, M. Tokizene and N. Fuusbiro (A Publication of JSRS, 1991) 373-378 T. Tsuzuki end A Takaha& Pmt. of 1st Japan Inkmational SAMPE Symposium (Nov. 28&c. 1,1989) 243 M.Kon, J. Kaneko and S. Sugamata, J the Japan Society for Tecbno~ogy of Plasticity, 35-402 (1994) 823-828 RAShabeni and T.W.Clyne, Materials Science & EnginecrinS,Al35 (1991) 281-285 T.G. Nieh and J. Wadsworth, Superplasticity in Advanced Materials edii by S. Hori, M. Tokkane and N. Furushiro (A Publication ofJSRS, 1991), 339-348 G. LZqemnce, T. Imai and B.Hong. ibid, 379-384 T. Imai, G.L ‘Esperance,B. Hong. M. Mabuchi, and Y. Tozawa, Advances io Powder Metallurgy & ParticulateMaterials-1992 compiled by J.M. Caus aad RM. German, 9 (1992) 181-194
Figure 1. Mirrostructureof (a) the as-cast and @) es-extnukd p-Si,N,w/6061 Al composiks.
loo-
10
Temperature Figure 2. The tensile strengthsofthe as-e-
/K
$-Si,N,w/ 6061 Al, as-cast a-Si,N,w/6061 AL
MECHANICAL
Vol. 32. No. 11
o!al
PROPERTIES
L
II
0.1
0.01
Strain Figure 3. The relationship ratios of 44 and 100.
1805
OF A SQUEEZE CAST ALLQY
I/S’
rate
between the flow stress and the strain rate of the @Si,N,w/6061
Al composite extruded with the extmsion
l-
l:Si~NdJ6051.Rl(Xts/q x
i
UX-P/Mj
A
A .A
0
/ A
=.
+ 0
0
Figure 4. Tlx relatioosbip between tbe total elmgatim and the strain rate of the j%Si,N,w/606 1 Al composite extruded with the extrusion ratios of44 and 100.
(a)Before test
(b) i: = 0.21 s-1 ( T= 818 K
Figure 5. Superplastic defomxl
sample ofthe (bSi,N,w/6061
Al wmposb.
1806
MECHANICAL. PROPERTIES
OF A SQUEEZE CAST ALLOY
Figure 6. Fracture surface ofthe p-Si,N,w/6061
Al composite pulled at the strain rate of 0.21 d.
Vol. 32, No. 11