hot extrusion of nanostructured al alloy powder: extrusion ratio and temperature effect on the...
TRANSCRIPT
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
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Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio andTemperature Effect on the Microstructure and Mechanical Properties
Peres M M1Fogagnolo JB
1 AH
1 Audebert F
2 Saporiti F
2 Jorge Jr AM
1 Kiminami CS
1Botta F
WJ1and Bolfarini C
1
1
Department of Materials Engineering ndash Federal University of Satildeo CarlosRod Washington Luiz km 235 ndash Satildeo Carlos ndash SP ndash Brazil - CEP 13565-905
Corresponding author moreirapowerufscarbr2Departamento de Ingenieria Mecacircnica - Facultad de Ingenieria - Universidad de Buenos Aires
Av Paseo Coloacuten 850 ndash Buenos Aires BA ndash Argentina
ABSTRACT
A nanostructured aluminium alloy powder prepared by rapid solidification via gas
atomization was consolidated into bulk material under various processing conditions via hot
extrusion The microstructure modifications and mechanical properties of the consolidated alloys as
a function of the extrusion conditions were investigated The increase in the extrusion-load with the
increase of extrusion-rate and decrease of temperature are shown and discussed in association withthe modification in the microstructures The differences in mechanical properties measured by
compressive tests are also discussed in association with the extrusion parameters Furthermore
suggestions are given for rationalising the extrusion ratio and temperature conditions for the
consolidation of nanostructured aluminium alloy powders via hot extrusion
INTRODUCTION
In the last years due to remarkable potentialities in terms of physical and mechanical
properties nanostructured materials have been subject of large amount of research [1ndash3] A variety
of techniques such as mechanical alloying and rapid solidification have been successfully used to prepare nanostructured materials [4] However powders or foils are usually the result of these
materials when they are prepared by the above mentioned methods and thus they cannot be directly
used for structural applications Consequently development of consolidation processes suitable fornanostructured materials are of interest associated mainly with nanostructured powder materials
The published research up to date has shown that extrusion is one of the most effective
processes for the powder materials consolidation [5ndash8] In the present work we investigated the
influence of the two main technical parameters strain rate and temperature of hot extrusion on the
microstructure and mechanical properties of the bulk material consolidated from nanostructured
aluminium alloy powder
MATERIALS AND METHODS
Rapidly solidified aluminium alloy powder with a nominal composition of Al-30Fe-
042Cu-037Mn (wt ) were prepared using argon gas atomisation The nanostructured aluminium
alloy powder with an average grain size of 25 nm microstructure was obtained The nanostructured
powder cylindrical preforms for consolidation processing with a relative density of about 0middot96 and
with initial diameter of 262 mm were prepared by cold pressing The preforms were then
consolidated into 79 mm diameter bars of bulk material by hot extrusion at 3 di983142983142 erent temperatures
375 400 and 425degC with an extrusion ratio of 101 and ram speed of 1 15 and 30 mms
Materials Science Forum Vol 570 (2008) pp 91-96 online at httpwwwscientificnet copy (2008) Trans Tech Publications Switzerland Online available since 2008Feb18
All rights reserved No part of contents of this paper may be repr oduced or transmitted in any form or by any means without the written permission of thepublisher Trans Tech Publications Ltd Switzerland wwwttpnet (ID 14310725255-130808043841)
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
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The mean extrusion strain rate was calculated using the following equation [9]
where V is the average ram speed DC is the container bore (262mm) DE is the diameter of the
extruded rod (79mm) and α is the dead-metal zone semiangle (60o)
The mechanical properties of the bulk material consolidated from nanostructured aluminium
alloy powder were determined by means of room-temperature compression tests which were
performed using the Interactive Instruments 1k-16 universal testing machine the compression speed
was 05 mmmin
The grain size of the as extruded alloy was characterised by X-ray di983142983142 raction using a Rigaku
diffractometer with Cu K α radiation Microstructural observations were carried out by transmission
electron microscopy (TEM) with a Philips CMndash120 microscope Thin foils for TEM observation
were prepared by ion milling
RESULTS AND DISCUSSION
Grain size and microstructure
To understand the strength and ductility achieved in the processed Al-30Fe-042Cu-037Mn
powder alloy the microstructure and phases constitution of the alloy have been investigated Fig 1
shows a zoom of the XRD pattern after extrusion from samples in three different temperatures Two
phases have been identified from the XRD patterns these are fcc-Al solid solution and Al3Fe One
can observe the substantial fcc-Al peak broadening with decreasing of extrusion temperature
suggesting nanosized fcc-Al grains and the Al3Fe peak contraction and intensity reduction with theextrusion temperature increasing indicating both precipitate coarsening and dissolution
30 35 40 45 50
2θθθθ (deg)
I n t e n s i t y
Al3Fe
375oC
400oC
425oC
Powder
Al3Fe
Figure 1 - XRD patterns of the processed bulk Al-30Fe-042Cu-037Mn powder alloy after
extrusion
Figure 2 shows the average grain size of the bulk aluminium alloy before and after
extrusion as a function of extrusion temperature The value at 25degC is the powder average grain
size The data points were fitted to a representative curve to obtain the approximate behaviour
between 25degC and the other temperatures It is believed that there is a critical temperature for grain
growth during consolidation by hot extrusion When the extrusion temperature is above the critical
one the average grain size of the consolidated alloy quickly increases with the extrusion
temperature increasing reaching about 69 nm at 425degC
The influence of temperature on grain growth rate (GGR) can be expressed in an Arrheniustype equation GGR asymp exp(minusQRT ) where Q is the activation energy for isothermal grain growth
92 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 36
R the molar gas constant and T the absolute temperature
If the grain growth of the nanostructured aluminium alloy during hot extrusion can be
considered as isothermal grain growth then the grain growth behaviour is mainly dependent on two
factors which govern the grain growth rate the activation energy (Q) and the extrusion temperature
(T) From the above equation it is clear that the rate is small when the activation energy is high or
the temperature is decreased Since nanosize grains usually have very high activation energy forgrain growth the GGR has a tendency to be smaller when the nanostructured aluminium alloy
powder undertakes hot extrusion at relatively low temperatures As a result it can be expected that
the grain growth will not be significant when the extrusion temperature is low If the activation
energy is unchanged according to the above equation with the enhancement of the extrusion
temperature the grain growth rate will be increased and thus causing faster grain growth In fact
when the extrusion process is performed within a relatively low temperature range the activation
energy of the nanostructured aluminium alloy will increase with increasing temperature due to the
precipitate effect that pin the grain boundary movement necessary for grain growth and thus when
the extrusion process is carried out at lower temperatures bellow the critical one the GGR can be
kept at relatively lower values and it can be expected that the grain growth is limited to a certain
amount But when the temperature is increased up to the critical value the coarsening anddissolving of the precipitates will occur with the temperature increasing leading to the reduction or
disappearance of the pinning effect of the precipitates and thus decreasing the activation energy
even as the effect of increasing temperature on enhancement of the GGR becomes more important
Therefore when the extrusion process is carried out at temperatures above the critical value the
value of the grain growth quickly increases and the grain growth during extrusion becomes more
remarkable
0
20
40
60
80
100
0 200 400 600
Temperature (C)
G r a i n S i z e ( n m )
Figure 2 - Dependence of the average grain size on extrusion temperature
Figure 3a shows TEM image of the aluminium powder alloy and the selected area electron
diffraction pattern (SAEDP) showing the fcc-Al pattern and the small grain dimension Also the
TEM analysis reveals the presence of small precipitates especially at grain boundaries inferred
from Fig 1 as Al3Fe and that the particle sizes of Al3Fe intermetallic precipitates are similar to thegrain size of fcc-Al all of which averaging about 25 nm Also the volume fraction of these
precipitates is about 8
Figure 3b shows TEM image of the as extruded bulk aluminium alloy consolidated from
nanostructured powder at 425oC and 293 s-1 It appears that the TEM observation of grain size
agrees well with the results of the XRD analysis shown in Fig 2 The main following
microstructural features which correspond to the final extrusion temperatures have been revealed
no obvious precipitation particles can be observed in the bulk material consolidated only in the
powder before the extrusion (Fig 3a) the quantity of the precipitated particles was found to have
reduced significantly indicating the precipitate dissolution and the significant enhancement on the
solubility of the alloying elements in aluminium at that temperature (which agrees with the XRD
pattern shown in Fig 1) Obviously the TEM observation results support the preceding analysis forthe grain growth of the nanostructured aluminium alloy during the extrusion process
Materials Science Forum Vol 570 93
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 46
(a) Powder (25 degC) (b) Extruded (425 degC)
Figure 3 - TEM images of bulk aluminium alloy consolidated at the indicated temperatures
Mechanical properties
Figure 4 shows the dependence of room temperature compressive mechanical properties for
the as extruded alloy on extrusion temperature The elongation of the as extruded alloy tends to
increase with the increasing of the extrusion temperature Also only within the range 375ndash400degC
does the elongation of the consolidated material increased significantly At higher temperatures(400ndash425degC) a small decrease in elongation with increasing temperature was observed As the
elongation of the bulk material consolidated from powders is extremely dependent on the
densification effects of the powder preform and the bonding condition of the alloy powders it is
believed that only when the extrusion temperature is around 400degC good properties for the
consolidated nanostructured aluminium powder can be obtained As for yield compressive strength
σs it has similar dependence on the extrusion temperature When the nanostructured aluminium
alloy powders are extruded at temperatures below 400degC even with the poor bonding of the
powders particles the consolidated material possesses reasonably high strength due to the fact that
grain growth during extrusion is small and due to the hardening effect resulting from the existent
precipitates Yet when the extrusion process is performed within the temperature range 375ndash400degC
the strength of the consolidated material is considerably reduced Perhaps this is a result of thecoherency breakdown between the precipitates and the matrix lattice and the precipitate coarsening
which leads to the disappearance of precipitation hardening The bonding condition of the powders
cannot be enhanced significantly within the temperature range 375ndash400degC When the extrusion tem-
perature is increased to the range 400ndash425degC the consolidated material strength tends to increase
again due to the significant enhancement of the powder bonding condition and the increase in the
alloy elements solubility in the matrix lattice even considering the grain growth that occurred during
the extrusion process
These results suggest that to obtain both high strength and good elongation the temperature
for hot extrusion of these nanostructured aluminium powders should be selected within the range
400ndash425degC when the extrusion temperature is increased above 425degC the strength of the
consolidated material will decrease with increasing temperature due to excessive grain growth
94 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 56
125
130
135
140
145
150
155
160
360 380 400 420 440
Temperature (C)
S t r
e s s σ σσ σ s ( M P a )
10
147
293
0
10
20
30
40
50
60
360 380 400 420 440
Temperature (C)
E l
o n g a t i o n ( )
10
147
293
Figure 4 - Dependence of room temperature compressive mechanical properties on extrusion
temperature
Figure 5 shows the dependence of the room temperature compressive mechanical properties
of the as extruded alloy on the strain rate in all temperature range One can note that both
compressive strength and elongation of the as extruded alloy increase with the increase in the strain
rate Increasing strain rate increases the pressure and the shear deformation that the powdersexperience during extrusion leading to improvement in the powder bonding to the densification
effect For extrusion strain rate higher than 147 s-1 the increase in mechanical properties of the as
extruded alloy is not noticeable This suggests that extrusion ratio of 147 s -1 can ensure good
bonding strength and full densification of the powder material Therefore the appropriate strain rate
for the hot extrusion of the nanostructured aluminium powder is 147 ndash 293 s-1 It can be noticed
that very high strain rate will only cause the rising of the process cost and will not do much to
increase the mechanical properties
110
120
130
140
150
160
0 10 20 30
Strain Rate (1s)
S t r e s s σ σσ σ s
( M P a )
425 C
400 C
375 C
0
10
20
30
40
50
60
0 10 20 30
Strain Rate (1s)
E l o n g a t i o
n ( )
375 C
400 C
425 C
Figure 5 - Dependence of room temperature compressive mechanical properties on extrusion ratio
CONCLUSIONS
The grain growth behaviour of the nanostructured aluminium alloy studied in this work during
extrusion is strongly dependent on the extrusion temperature
The bonding strength of the nanostructured aluminium powder is susceptible to the extrusion
temperature
A larger extrusion ratio is useful to increase the powder bonding strength and the densification
e983142983142 ect as a result both the elongation and the compressive strength of the consolidated material will
give rise to the enhancement
Materials Science Forum Vol 570 95
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 66
REFERENCES
1 - J B Fogagnolo M H Robert E M Ruiz-Navas and M Torralba Journal of Materials
Science 2002 37 4603 ndash 4607
2 - L Ma T F Zahrah R Fields - Processing And Simulation Of Consolidation Of
Amorphous Aluminum-Based Powder Material in Proceedings of IMECrsquo03 2003 ASMEIntern Mech Eng Cong Washington DC Nov 15-21 2003
3 - MD Salvador V Amigoacute N Martinez DJ Busquets Journal of Materials Processing
Technology 2003 143ndash144 605ndash611
4 - C Suryanarayana Int Mater Rev 1995 40 (2) 41
5 - L Hu Z Li and E Wang Powder Metallurgy 1999 Vol 42 No 2 153
6 - K Ohuchi And H J Takahash Bull Jpn Inst Met 1983 47 ( 3) 258
7 - N Inoue And M Nishara lsquoHydrostatic Extrusion ndash Theory And Applicationrsquo 1985
Oxford Elsevier
8 - Z Li Et Al Chin J Nonferrous Met 1995 5 ( 4) 102
9 - AF Castle and T Sheppard Hot Working Theory Applied to Extrusion of Some Aluminum
Alloys Met Technol 1976 3 (10) 1976
96 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 26
The mean extrusion strain rate was calculated using the following equation [9]
where V is the average ram speed DC is the container bore (262mm) DE is the diameter of the
extruded rod (79mm) and α is the dead-metal zone semiangle (60o)
The mechanical properties of the bulk material consolidated from nanostructured aluminium
alloy powder were determined by means of room-temperature compression tests which were
performed using the Interactive Instruments 1k-16 universal testing machine the compression speed
was 05 mmmin
The grain size of the as extruded alloy was characterised by X-ray di983142983142 raction using a Rigaku
diffractometer with Cu K α radiation Microstructural observations were carried out by transmission
electron microscopy (TEM) with a Philips CMndash120 microscope Thin foils for TEM observation
were prepared by ion milling
RESULTS AND DISCUSSION
Grain size and microstructure
To understand the strength and ductility achieved in the processed Al-30Fe-042Cu-037Mn
powder alloy the microstructure and phases constitution of the alloy have been investigated Fig 1
shows a zoom of the XRD pattern after extrusion from samples in three different temperatures Two
phases have been identified from the XRD patterns these are fcc-Al solid solution and Al3Fe One
can observe the substantial fcc-Al peak broadening with decreasing of extrusion temperature
suggesting nanosized fcc-Al grains and the Al3Fe peak contraction and intensity reduction with theextrusion temperature increasing indicating both precipitate coarsening and dissolution
30 35 40 45 50
2θθθθ (deg)
I n t e n s i t y
Al3Fe
375oC
400oC
425oC
Powder
Al3Fe
Figure 1 - XRD patterns of the processed bulk Al-30Fe-042Cu-037Mn powder alloy after
extrusion
Figure 2 shows the average grain size of the bulk aluminium alloy before and after
extrusion as a function of extrusion temperature The value at 25degC is the powder average grain
size The data points were fitted to a representative curve to obtain the approximate behaviour
between 25degC and the other temperatures It is believed that there is a critical temperature for grain
growth during consolidation by hot extrusion When the extrusion temperature is above the critical
one the average grain size of the consolidated alloy quickly increases with the extrusion
temperature increasing reaching about 69 nm at 425degC
The influence of temperature on grain growth rate (GGR) can be expressed in an Arrheniustype equation GGR asymp exp(minusQRT ) where Q is the activation energy for isothermal grain growth
92 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 36
R the molar gas constant and T the absolute temperature
If the grain growth of the nanostructured aluminium alloy during hot extrusion can be
considered as isothermal grain growth then the grain growth behaviour is mainly dependent on two
factors which govern the grain growth rate the activation energy (Q) and the extrusion temperature
(T) From the above equation it is clear that the rate is small when the activation energy is high or
the temperature is decreased Since nanosize grains usually have very high activation energy forgrain growth the GGR has a tendency to be smaller when the nanostructured aluminium alloy
powder undertakes hot extrusion at relatively low temperatures As a result it can be expected that
the grain growth will not be significant when the extrusion temperature is low If the activation
energy is unchanged according to the above equation with the enhancement of the extrusion
temperature the grain growth rate will be increased and thus causing faster grain growth In fact
when the extrusion process is performed within a relatively low temperature range the activation
energy of the nanostructured aluminium alloy will increase with increasing temperature due to the
precipitate effect that pin the grain boundary movement necessary for grain growth and thus when
the extrusion process is carried out at lower temperatures bellow the critical one the GGR can be
kept at relatively lower values and it can be expected that the grain growth is limited to a certain
amount But when the temperature is increased up to the critical value the coarsening anddissolving of the precipitates will occur with the temperature increasing leading to the reduction or
disappearance of the pinning effect of the precipitates and thus decreasing the activation energy
even as the effect of increasing temperature on enhancement of the GGR becomes more important
Therefore when the extrusion process is carried out at temperatures above the critical value the
value of the grain growth quickly increases and the grain growth during extrusion becomes more
remarkable
0
20
40
60
80
100
0 200 400 600
Temperature (C)
G r a i n S i z e ( n m )
Figure 2 - Dependence of the average grain size on extrusion temperature
Figure 3a shows TEM image of the aluminium powder alloy and the selected area electron
diffraction pattern (SAEDP) showing the fcc-Al pattern and the small grain dimension Also the
TEM analysis reveals the presence of small precipitates especially at grain boundaries inferred
from Fig 1 as Al3Fe and that the particle sizes of Al3Fe intermetallic precipitates are similar to thegrain size of fcc-Al all of which averaging about 25 nm Also the volume fraction of these
precipitates is about 8
Figure 3b shows TEM image of the as extruded bulk aluminium alloy consolidated from
nanostructured powder at 425oC and 293 s-1 It appears that the TEM observation of grain size
agrees well with the results of the XRD analysis shown in Fig 2 The main following
microstructural features which correspond to the final extrusion temperatures have been revealed
no obvious precipitation particles can be observed in the bulk material consolidated only in the
powder before the extrusion (Fig 3a) the quantity of the precipitated particles was found to have
reduced significantly indicating the precipitate dissolution and the significant enhancement on the
solubility of the alloying elements in aluminium at that temperature (which agrees with the XRD
pattern shown in Fig 1) Obviously the TEM observation results support the preceding analysis forthe grain growth of the nanostructured aluminium alloy during the extrusion process
Materials Science Forum Vol 570 93
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 46
(a) Powder (25 degC) (b) Extruded (425 degC)
Figure 3 - TEM images of bulk aluminium alloy consolidated at the indicated temperatures
Mechanical properties
Figure 4 shows the dependence of room temperature compressive mechanical properties for
the as extruded alloy on extrusion temperature The elongation of the as extruded alloy tends to
increase with the increasing of the extrusion temperature Also only within the range 375ndash400degC
does the elongation of the consolidated material increased significantly At higher temperatures(400ndash425degC) a small decrease in elongation with increasing temperature was observed As the
elongation of the bulk material consolidated from powders is extremely dependent on the
densification effects of the powder preform and the bonding condition of the alloy powders it is
believed that only when the extrusion temperature is around 400degC good properties for the
consolidated nanostructured aluminium powder can be obtained As for yield compressive strength
σs it has similar dependence on the extrusion temperature When the nanostructured aluminium
alloy powders are extruded at temperatures below 400degC even with the poor bonding of the
powders particles the consolidated material possesses reasonably high strength due to the fact that
grain growth during extrusion is small and due to the hardening effect resulting from the existent
precipitates Yet when the extrusion process is performed within the temperature range 375ndash400degC
the strength of the consolidated material is considerably reduced Perhaps this is a result of thecoherency breakdown between the precipitates and the matrix lattice and the precipitate coarsening
which leads to the disappearance of precipitation hardening The bonding condition of the powders
cannot be enhanced significantly within the temperature range 375ndash400degC When the extrusion tem-
perature is increased to the range 400ndash425degC the consolidated material strength tends to increase
again due to the significant enhancement of the powder bonding condition and the increase in the
alloy elements solubility in the matrix lattice even considering the grain growth that occurred during
the extrusion process
These results suggest that to obtain both high strength and good elongation the temperature
for hot extrusion of these nanostructured aluminium powders should be selected within the range
400ndash425degC when the extrusion temperature is increased above 425degC the strength of the
consolidated material will decrease with increasing temperature due to excessive grain growth
94 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 56
125
130
135
140
145
150
155
160
360 380 400 420 440
Temperature (C)
S t r
e s s σ σσ σ s ( M P a )
10
147
293
0
10
20
30
40
50
60
360 380 400 420 440
Temperature (C)
E l
o n g a t i o n ( )
10
147
293
Figure 4 - Dependence of room temperature compressive mechanical properties on extrusion
temperature
Figure 5 shows the dependence of the room temperature compressive mechanical properties
of the as extruded alloy on the strain rate in all temperature range One can note that both
compressive strength and elongation of the as extruded alloy increase with the increase in the strain
rate Increasing strain rate increases the pressure and the shear deformation that the powdersexperience during extrusion leading to improvement in the powder bonding to the densification
effect For extrusion strain rate higher than 147 s-1 the increase in mechanical properties of the as
extruded alloy is not noticeable This suggests that extrusion ratio of 147 s -1 can ensure good
bonding strength and full densification of the powder material Therefore the appropriate strain rate
for the hot extrusion of the nanostructured aluminium powder is 147 ndash 293 s-1 It can be noticed
that very high strain rate will only cause the rising of the process cost and will not do much to
increase the mechanical properties
110
120
130
140
150
160
0 10 20 30
Strain Rate (1s)
S t r e s s σ σσ σ s
( M P a )
425 C
400 C
375 C
0
10
20
30
40
50
60
0 10 20 30
Strain Rate (1s)
E l o n g a t i o
n ( )
375 C
400 C
425 C
Figure 5 - Dependence of room temperature compressive mechanical properties on extrusion ratio
CONCLUSIONS
The grain growth behaviour of the nanostructured aluminium alloy studied in this work during
extrusion is strongly dependent on the extrusion temperature
The bonding strength of the nanostructured aluminium powder is susceptible to the extrusion
temperature
A larger extrusion ratio is useful to increase the powder bonding strength and the densification
e983142983142 ect as a result both the elongation and the compressive strength of the consolidated material will
give rise to the enhancement
Materials Science Forum Vol 570 95
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 66
REFERENCES
1 - J B Fogagnolo M H Robert E M Ruiz-Navas and M Torralba Journal of Materials
Science 2002 37 4603 ndash 4607
2 - L Ma T F Zahrah R Fields - Processing And Simulation Of Consolidation Of
Amorphous Aluminum-Based Powder Material in Proceedings of IMECrsquo03 2003 ASMEIntern Mech Eng Cong Washington DC Nov 15-21 2003
3 - MD Salvador V Amigoacute N Martinez DJ Busquets Journal of Materials Processing
Technology 2003 143ndash144 605ndash611
4 - C Suryanarayana Int Mater Rev 1995 40 (2) 41
5 - L Hu Z Li and E Wang Powder Metallurgy 1999 Vol 42 No 2 153
6 - K Ohuchi And H J Takahash Bull Jpn Inst Met 1983 47 ( 3) 258
7 - N Inoue And M Nishara lsquoHydrostatic Extrusion ndash Theory And Applicationrsquo 1985
Oxford Elsevier
8 - Z Li Et Al Chin J Nonferrous Met 1995 5 ( 4) 102
9 - AF Castle and T Sheppard Hot Working Theory Applied to Extrusion of Some Aluminum
Alloys Met Technol 1976 3 (10) 1976
96 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 36
R the molar gas constant and T the absolute temperature
If the grain growth of the nanostructured aluminium alloy during hot extrusion can be
considered as isothermal grain growth then the grain growth behaviour is mainly dependent on two
factors which govern the grain growth rate the activation energy (Q) and the extrusion temperature
(T) From the above equation it is clear that the rate is small when the activation energy is high or
the temperature is decreased Since nanosize grains usually have very high activation energy forgrain growth the GGR has a tendency to be smaller when the nanostructured aluminium alloy
powder undertakes hot extrusion at relatively low temperatures As a result it can be expected that
the grain growth will not be significant when the extrusion temperature is low If the activation
energy is unchanged according to the above equation with the enhancement of the extrusion
temperature the grain growth rate will be increased and thus causing faster grain growth In fact
when the extrusion process is performed within a relatively low temperature range the activation
energy of the nanostructured aluminium alloy will increase with increasing temperature due to the
precipitate effect that pin the grain boundary movement necessary for grain growth and thus when
the extrusion process is carried out at lower temperatures bellow the critical one the GGR can be
kept at relatively lower values and it can be expected that the grain growth is limited to a certain
amount But when the temperature is increased up to the critical value the coarsening anddissolving of the precipitates will occur with the temperature increasing leading to the reduction or
disappearance of the pinning effect of the precipitates and thus decreasing the activation energy
even as the effect of increasing temperature on enhancement of the GGR becomes more important
Therefore when the extrusion process is carried out at temperatures above the critical value the
value of the grain growth quickly increases and the grain growth during extrusion becomes more
remarkable
0
20
40
60
80
100
0 200 400 600
Temperature (C)
G r a i n S i z e ( n m )
Figure 2 - Dependence of the average grain size on extrusion temperature
Figure 3a shows TEM image of the aluminium powder alloy and the selected area electron
diffraction pattern (SAEDP) showing the fcc-Al pattern and the small grain dimension Also the
TEM analysis reveals the presence of small precipitates especially at grain boundaries inferred
from Fig 1 as Al3Fe and that the particle sizes of Al3Fe intermetallic precipitates are similar to thegrain size of fcc-Al all of which averaging about 25 nm Also the volume fraction of these
precipitates is about 8
Figure 3b shows TEM image of the as extruded bulk aluminium alloy consolidated from
nanostructured powder at 425oC and 293 s-1 It appears that the TEM observation of grain size
agrees well with the results of the XRD analysis shown in Fig 2 The main following
microstructural features which correspond to the final extrusion temperatures have been revealed
no obvious precipitation particles can be observed in the bulk material consolidated only in the
powder before the extrusion (Fig 3a) the quantity of the precipitated particles was found to have
reduced significantly indicating the precipitate dissolution and the significant enhancement on the
solubility of the alloying elements in aluminium at that temperature (which agrees with the XRD
pattern shown in Fig 1) Obviously the TEM observation results support the preceding analysis forthe grain growth of the nanostructured aluminium alloy during the extrusion process
Materials Science Forum Vol 570 93
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 46
(a) Powder (25 degC) (b) Extruded (425 degC)
Figure 3 - TEM images of bulk aluminium alloy consolidated at the indicated temperatures
Mechanical properties
Figure 4 shows the dependence of room temperature compressive mechanical properties for
the as extruded alloy on extrusion temperature The elongation of the as extruded alloy tends to
increase with the increasing of the extrusion temperature Also only within the range 375ndash400degC
does the elongation of the consolidated material increased significantly At higher temperatures(400ndash425degC) a small decrease in elongation with increasing temperature was observed As the
elongation of the bulk material consolidated from powders is extremely dependent on the
densification effects of the powder preform and the bonding condition of the alloy powders it is
believed that only when the extrusion temperature is around 400degC good properties for the
consolidated nanostructured aluminium powder can be obtained As for yield compressive strength
σs it has similar dependence on the extrusion temperature When the nanostructured aluminium
alloy powders are extruded at temperatures below 400degC even with the poor bonding of the
powders particles the consolidated material possesses reasonably high strength due to the fact that
grain growth during extrusion is small and due to the hardening effect resulting from the existent
precipitates Yet when the extrusion process is performed within the temperature range 375ndash400degC
the strength of the consolidated material is considerably reduced Perhaps this is a result of thecoherency breakdown between the precipitates and the matrix lattice and the precipitate coarsening
which leads to the disappearance of precipitation hardening The bonding condition of the powders
cannot be enhanced significantly within the temperature range 375ndash400degC When the extrusion tem-
perature is increased to the range 400ndash425degC the consolidated material strength tends to increase
again due to the significant enhancement of the powder bonding condition and the increase in the
alloy elements solubility in the matrix lattice even considering the grain growth that occurred during
the extrusion process
These results suggest that to obtain both high strength and good elongation the temperature
for hot extrusion of these nanostructured aluminium powders should be selected within the range
400ndash425degC when the extrusion temperature is increased above 425degC the strength of the
consolidated material will decrease with increasing temperature due to excessive grain growth
94 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 56
125
130
135
140
145
150
155
160
360 380 400 420 440
Temperature (C)
S t r
e s s σ σσ σ s ( M P a )
10
147
293
0
10
20
30
40
50
60
360 380 400 420 440
Temperature (C)
E l
o n g a t i o n ( )
10
147
293
Figure 4 - Dependence of room temperature compressive mechanical properties on extrusion
temperature
Figure 5 shows the dependence of the room temperature compressive mechanical properties
of the as extruded alloy on the strain rate in all temperature range One can note that both
compressive strength and elongation of the as extruded alloy increase with the increase in the strain
rate Increasing strain rate increases the pressure and the shear deformation that the powdersexperience during extrusion leading to improvement in the powder bonding to the densification
effect For extrusion strain rate higher than 147 s-1 the increase in mechanical properties of the as
extruded alloy is not noticeable This suggests that extrusion ratio of 147 s -1 can ensure good
bonding strength and full densification of the powder material Therefore the appropriate strain rate
for the hot extrusion of the nanostructured aluminium powder is 147 ndash 293 s-1 It can be noticed
that very high strain rate will only cause the rising of the process cost and will not do much to
increase the mechanical properties
110
120
130
140
150
160
0 10 20 30
Strain Rate (1s)
S t r e s s σ σσ σ s
( M P a )
425 C
400 C
375 C
0
10
20
30
40
50
60
0 10 20 30
Strain Rate (1s)
E l o n g a t i o
n ( )
375 C
400 C
425 C
Figure 5 - Dependence of room temperature compressive mechanical properties on extrusion ratio
CONCLUSIONS
The grain growth behaviour of the nanostructured aluminium alloy studied in this work during
extrusion is strongly dependent on the extrusion temperature
The bonding strength of the nanostructured aluminium powder is susceptible to the extrusion
temperature
A larger extrusion ratio is useful to increase the powder bonding strength and the densification
e983142983142 ect as a result both the elongation and the compressive strength of the consolidated material will
give rise to the enhancement
Materials Science Forum Vol 570 95
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 66
REFERENCES
1 - J B Fogagnolo M H Robert E M Ruiz-Navas and M Torralba Journal of Materials
Science 2002 37 4603 ndash 4607
2 - L Ma T F Zahrah R Fields - Processing And Simulation Of Consolidation Of
Amorphous Aluminum-Based Powder Material in Proceedings of IMECrsquo03 2003 ASMEIntern Mech Eng Cong Washington DC Nov 15-21 2003
3 - MD Salvador V Amigoacute N Martinez DJ Busquets Journal of Materials Processing
Technology 2003 143ndash144 605ndash611
4 - C Suryanarayana Int Mater Rev 1995 40 (2) 41
5 - L Hu Z Li and E Wang Powder Metallurgy 1999 Vol 42 No 2 153
6 - K Ohuchi And H J Takahash Bull Jpn Inst Met 1983 47 ( 3) 258
7 - N Inoue And M Nishara lsquoHydrostatic Extrusion ndash Theory And Applicationrsquo 1985
Oxford Elsevier
8 - Z Li Et Al Chin J Nonferrous Met 1995 5 ( 4) 102
9 - AF Castle and T Sheppard Hot Working Theory Applied to Extrusion of Some Aluminum
Alloys Met Technol 1976 3 (10) 1976
96 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 46
(a) Powder (25 degC) (b) Extruded (425 degC)
Figure 3 - TEM images of bulk aluminium alloy consolidated at the indicated temperatures
Mechanical properties
Figure 4 shows the dependence of room temperature compressive mechanical properties for
the as extruded alloy on extrusion temperature The elongation of the as extruded alloy tends to
increase with the increasing of the extrusion temperature Also only within the range 375ndash400degC
does the elongation of the consolidated material increased significantly At higher temperatures(400ndash425degC) a small decrease in elongation with increasing temperature was observed As the
elongation of the bulk material consolidated from powders is extremely dependent on the
densification effects of the powder preform and the bonding condition of the alloy powders it is
believed that only when the extrusion temperature is around 400degC good properties for the
consolidated nanostructured aluminium powder can be obtained As for yield compressive strength
σs it has similar dependence on the extrusion temperature When the nanostructured aluminium
alloy powders are extruded at temperatures below 400degC even with the poor bonding of the
powders particles the consolidated material possesses reasonably high strength due to the fact that
grain growth during extrusion is small and due to the hardening effect resulting from the existent
precipitates Yet when the extrusion process is performed within the temperature range 375ndash400degC
the strength of the consolidated material is considerably reduced Perhaps this is a result of thecoherency breakdown between the precipitates and the matrix lattice and the precipitate coarsening
which leads to the disappearance of precipitation hardening The bonding condition of the powders
cannot be enhanced significantly within the temperature range 375ndash400degC When the extrusion tem-
perature is increased to the range 400ndash425degC the consolidated material strength tends to increase
again due to the significant enhancement of the powder bonding condition and the increase in the
alloy elements solubility in the matrix lattice even considering the grain growth that occurred during
the extrusion process
These results suggest that to obtain both high strength and good elongation the temperature
for hot extrusion of these nanostructured aluminium powders should be selected within the range
400ndash425degC when the extrusion temperature is increased above 425degC the strength of the
consolidated material will decrease with increasing temperature due to excessive grain growth
94 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 56
125
130
135
140
145
150
155
160
360 380 400 420 440
Temperature (C)
S t r
e s s σ σσ σ s ( M P a )
10
147
293
0
10
20
30
40
50
60
360 380 400 420 440
Temperature (C)
E l
o n g a t i o n ( )
10
147
293
Figure 4 - Dependence of room temperature compressive mechanical properties on extrusion
temperature
Figure 5 shows the dependence of the room temperature compressive mechanical properties
of the as extruded alloy on the strain rate in all temperature range One can note that both
compressive strength and elongation of the as extruded alloy increase with the increase in the strain
rate Increasing strain rate increases the pressure and the shear deformation that the powdersexperience during extrusion leading to improvement in the powder bonding to the densification
effect For extrusion strain rate higher than 147 s-1 the increase in mechanical properties of the as
extruded alloy is not noticeable This suggests that extrusion ratio of 147 s -1 can ensure good
bonding strength and full densification of the powder material Therefore the appropriate strain rate
for the hot extrusion of the nanostructured aluminium powder is 147 ndash 293 s-1 It can be noticed
that very high strain rate will only cause the rising of the process cost and will not do much to
increase the mechanical properties
110
120
130
140
150
160
0 10 20 30
Strain Rate (1s)
S t r e s s σ σσ σ s
( M P a )
425 C
400 C
375 C
0
10
20
30
40
50
60
0 10 20 30
Strain Rate (1s)
E l o n g a t i o
n ( )
375 C
400 C
425 C
Figure 5 - Dependence of room temperature compressive mechanical properties on extrusion ratio
CONCLUSIONS
The grain growth behaviour of the nanostructured aluminium alloy studied in this work during
extrusion is strongly dependent on the extrusion temperature
The bonding strength of the nanostructured aluminium powder is susceptible to the extrusion
temperature
A larger extrusion ratio is useful to increase the powder bonding strength and the densification
e983142983142 ect as a result both the elongation and the compressive strength of the consolidated material will
give rise to the enhancement
Materials Science Forum Vol 570 95
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 66
REFERENCES
1 - J B Fogagnolo M H Robert E M Ruiz-Navas and M Torralba Journal of Materials
Science 2002 37 4603 ndash 4607
2 - L Ma T F Zahrah R Fields - Processing And Simulation Of Consolidation Of
Amorphous Aluminum-Based Powder Material in Proceedings of IMECrsquo03 2003 ASMEIntern Mech Eng Cong Washington DC Nov 15-21 2003
3 - MD Salvador V Amigoacute N Martinez DJ Busquets Journal of Materials Processing
Technology 2003 143ndash144 605ndash611
4 - C Suryanarayana Int Mater Rev 1995 40 (2) 41
5 - L Hu Z Li and E Wang Powder Metallurgy 1999 Vol 42 No 2 153
6 - K Ohuchi And H J Takahash Bull Jpn Inst Met 1983 47 ( 3) 258
7 - N Inoue And M Nishara lsquoHydrostatic Extrusion ndash Theory And Applicationrsquo 1985
Oxford Elsevier
8 - Z Li Et Al Chin J Nonferrous Met 1995 5 ( 4) 102
9 - AF Castle and T Sheppard Hot Working Theory Applied to Extrusion of Some Aluminum
Alloys Met Technol 1976 3 (10) 1976
96 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 56
125
130
135
140
145
150
155
160
360 380 400 420 440
Temperature (C)
S t r
e s s σ σσ σ s ( M P a )
10
147
293
0
10
20
30
40
50
60
360 380 400 420 440
Temperature (C)
E l
o n g a t i o n ( )
10
147
293
Figure 4 - Dependence of room temperature compressive mechanical properties on extrusion
temperature
Figure 5 shows the dependence of the room temperature compressive mechanical properties
of the as extruded alloy on the strain rate in all temperature range One can note that both
compressive strength and elongation of the as extruded alloy increase with the increase in the strain
rate Increasing strain rate increases the pressure and the shear deformation that the powdersexperience during extrusion leading to improvement in the powder bonding to the densification
effect For extrusion strain rate higher than 147 s-1 the increase in mechanical properties of the as
extruded alloy is not noticeable This suggests that extrusion ratio of 147 s -1 can ensure good
bonding strength and full densification of the powder material Therefore the appropriate strain rate
for the hot extrusion of the nanostructured aluminium powder is 147 ndash 293 s-1 It can be noticed
that very high strain rate will only cause the rising of the process cost and will not do much to
increase the mechanical properties
110
120
130
140
150
160
0 10 20 30
Strain Rate (1s)
S t r e s s σ σσ σ s
( M P a )
425 C
400 C
375 C
0
10
20
30
40
50
60
0 10 20 30
Strain Rate (1s)
E l o n g a t i o
n ( )
375 C
400 C
425 C
Figure 5 - Dependence of room temperature compressive mechanical properties on extrusion ratio
CONCLUSIONS
The grain growth behaviour of the nanostructured aluminium alloy studied in this work during
extrusion is strongly dependent on the extrusion temperature
The bonding strength of the nanostructured aluminium powder is susceptible to the extrusion
temperature
A larger extrusion ratio is useful to increase the powder bonding strength and the densification
e983142983142 ect as a result both the elongation and the compressive strength of the consolidated material will
give rise to the enhancement
Materials Science Forum Vol 570 95
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 66
REFERENCES
1 - J B Fogagnolo M H Robert E M Ruiz-Navas and M Torralba Journal of Materials
Science 2002 37 4603 ndash 4607
2 - L Ma T F Zahrah R Fields - Processing And Simulation Of Consolidation Of
Amorphous Aluminum-Based Powder Material in Proceedings of IMECrsquo03 2003 ASMEIntern Mech Eng Cong Washington DC Nov 15-21 2003
3 - MD Salvador V Amigoacute N Martinez DJ Busquets Journal of Materials Processing
Technology 2003 143ndash144 605ndash611
4 - C Suryanarayana Int Mater Rev 1995 40 (2) 41
5 - L Hu Z Li and E Wang Powder Metallurgy 1999 Vol 42 No 2 153
6 - K Ohuchi And H J Takahash Bull Jpn Inst Met 1983 47 ( 3) 258
7 - N Inoue And M Nishara lsquoHydrostatic Extrusion ndash Theory And Applicationrsquo 1985
Oxford Elsevier
8 - Z Li Et Al Chin J Nonferrous Met 1995 5 ( 4) 102
9 - AF Castle and T Sheppard Hot Working Theory Applied to Extrusion of Some Aluminum
Alloys Met Technol 1976 3 (10) 1976
96 Metastable and Nanostructured Materials III
8102019 Hot Extrusion of Nanostructured Al Alloy Powder Extrusion Ratio and Temperature Effect on the Microstructure anhellip
httpslidepdfcomreaderfullhot-extrusion-of-nanostructured-al-alloy-powder-extrusion-ratio-and-temperature 66
REFERENCES
1 - J B Fogagnolo M H Robert E M Ruiz-Navas and M Torralba Journal of Materials
Science 2002 37 4603 ndash 4607
2 - L Ma T F Zahrah R Fields - Processing And Simulation Of Consolidation Of
Amorphous Aluminum-Based Powder Material in Proceedings of IMECrsquo03 2003 ASMEIntern Mech Eng Cong Washington DC Nov 15-21 2003
3 - MD Salvador V Amigoacute N Martinez DJ Busquets Journal of Materials Processing
Technology 2003 143ndash144 605ndash611
4 - C Suryanarayana Int Mater Rev 1995 40 (2) 41
5 - L Hu Z Li and E Wang Powder Metallurgy 1999 Vol 42 No 2 153
6 - K Ohuchi And H J Takahash Bull Jpn Inst Met 1983 47 ( 3) 258
7 - N Inoue And M Nishara lsquoHydrostatic Extrusion ndash Theory And Applicationrsquo 1985
Oxford Elsevier
8 - Z Li Et Al Chin J Nonferrous Met 1995 5 ( 4) 102
9 - AF Castle and T Sheppard Hot Working Theory Applied to Extrusion of Some Aluminum
Alloys Met Technol 1976 3 (10) 1976
96 Metastable and Nanostructured Materials III