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Co-extrusion of Dual Aluminum Alloys with Special Surface Properties
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Available online at www.sciencedirect.com Procedia Engineering Engineering 00 00 (2017) (2017) 000–000 000–000 Procedia
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Procedia Engineering 207 (2017) 413–418
International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom
Co-extrusion of Dual Aluminum Alloys with Special Surface Properties a a b c d Xiang Maa*, Christian J. Simensena, Rune Østhusb, Wilhelm Dallc, Harald Kalagerd, Hans J. Rovendd, Leigang Wangee SINTEF SINTEF Materials Materials and and Chemistry, Chemistry, P.O.Box P.O.Box 124, 124, Blindern, Blindern, 0314 0314 Oslo, Oslo, Norway Norway SINTEF Raufoss Raufoss Manufacturing Manufacturing AS, AS, P.O.Box P.O.Box 163, 163, Raufoss, Raufoss, 2831 2831 Raufoss, Raufoss, Norway Norway SINTEF cc SINTEF SINTEF Materials Materials and and Chemistry, Chemistry, P.O. P.O. Box Box 4760, 4760, Sluppen, Sluppen, 7465 7465 Trondheim, Trondheim, Norway Norway ddDepartment of Materials Science and Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway Department of Materials Science and Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway ee School School of of Materials Materials Science Science and and Engineering, Engineering, Jiangsu Jiangsu University, University, Zhenjiang Zhenjiang 212013, 212013, China China a a
b b
Abstract Abstract Co-extrusion Co-extrusion method method is is used used for for production production of of aa dual dual Aluminum Aluminum rod. rod. The The surface surface layer layer material material for for co-extrusion co-extrusion is is prepared prepared by by rapid solidification process. The alloys Al4.5Mg1.0Ag (wt%) and Al4.5Mg are selected as the surface and the bulk rapid solidification process. The alloys Al4.5Mg1.0Ag (wt%) and Al4.5Mg are selected as the surface and the bulk materials, materials, respectively, and and are are co-extruded co-extruded at at high high temperature temperature range range (450480C). (450480C). The The microstructures microstructures of of rapid rapid solidified solidified Al Al in in co-extruded co-extruded respectively, rod consist consist of of small small grains grains (50µm) (50µm) and and some some small small particles particles (0.11µm). (0.11µm). A A proper proper annealing annealing on on the the extruded extruded rod rod increases increases the the rod surface surface hardness hardness more more than than 30%. 30%. Since Since the the co-extruded co-extruded material material contains contains small small T-phase T-phase particles, particles, this this increase increase in in hardness hardness indicates indicates precipitation precipitation of of aa metastable metastable MgAg MgAg phase phase or or aa MgAgAl MgAgAl phase phase at at 160C 160C during during annealing. annealing. © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. © © 2017 The Authors. Published by Elsevier Ltd. the scientific committee of the International Conference on the Technology Peer-review under responsibility of Peer-review under under responsibility responsibility of of the Peer-review scientific committee of the International Conference on the Technology of Plasticity. of Plasticity.. Keywords: Rapid Rapid solidification; solidification; Co-extrusion; Co-extrusion; Aluminium Aluminium alloy; alloy; Silver. Silver. Keywords:
1. Introduction As a crucial engineering material, Aluminum alloys are increasingly used in the automotive and transport
* * Corresponding Corresponding author. author. Tel.: Tel.: +47-98243925; +47-98243925; fax: fax: +47-22067350. +47-22067350. E-mail address: address: [email protected] [email protected] E-mail 1877-7058 1877-7058 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. Peer-review under under responsibility responsibility of of the scientific committee Peer-review Plasticity..
of the International Conference on the Technology of
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. 10.1016/j.proeng.2017.10.797
Xiang Ma et al. / Procedia Engineering 207 (2017) 413–418 X. Ma / Procedia Engineering 00 (2017) 000–000
414 2
industries, which have become the fastest growing markets for Al suppliers. The conventional process route for production of Al products, such as extruded sections, tubes or forged products is DC (direct chilled) casting, followed by homogenization, extrusion, forging and age hardening. For high-alloyed materials, this process route has its limitations because the solidification during DC casting is so slow that the material generates large macro-segregations if the alloying content is above 5–10 wt% [1, 2]. An alternative to the conventional DC casting process for such alloys is the rapid solidification process [3]. With this process, it is possible to achieve a very small-scaled crystalline structure and a homogeneous microstructure even for high alloyed materials. These factors can contribute to significant improvement with regard to material properties, with high yield strength, excellent fatigue resistant properties, reasonable ductility, high wear resistance and low thermal expansion coefficient. Such materials therefore have a great potential for automotive, aerospace and defense applications. Various production techniques are used to produce rapid solidified (RS) material. Both melt spinning process and centrifuge melt spinning process are developed in SINTEF and NTNU [4, 5] for RS Al production. During the melt spinning process, liquid Al is poured onto a fast-rotating copper wheel, causing very rapid solidification and forming a very thin metal ribbon. Our previous investigations [4, 5] have shown that RS Al alloys with excellent fatigue resistant properties can be obtained with only small intermetallic particles. Excellent properties with high pitting corrosion resistance can also be made from Al materials even without particles. Alloying elements with a high solubility, such as magnesium, zinc, silver and to some extent manganese, copper and chromium, are highly desirable for such purpose. To improve the production efficiency of lightweight parts through the combination of multi-materials and forming technologies, this investigation aims to examine the possibility to combine the production of RS Al-material with coextrusion method for production of a dual Al rod with high strength and/or excellent corrosion resistant properties at the surface and a ductile alloy in the bulk. As the surface layer is expected to be thin, pure Al without the common impurities and more exotic elements like Ag, Sc etc. can be used in the RS material for making the surface layer. The commercial Al materials as the bulk alloy also should have a low content of impurities. In doing so, a process route through production of RS Al, compaction of RS Al ribbons, and co-extrusion of RS Al with base Al alloys is proposed. The first part in this paper focuses on alloying for Al RS and base metals, rapid solidification, compacting of the RS material and successive co-extrusion. The second part is the microstructure analysis by EDS and hardness measurement of the co-extruded material, and annealing of the co-extruded rod and subsequent analysis. 2. Experimental 2.1. Alloying The base material is Al-4.5wt%Mg produced in Hydro Aluminium at Sunndal Verk. The compositions are determined by emission spectrometer. The main result is seen in Table 1. The material is grain refined with about 66 ppm borides, and is also expected to be refined by 64 ppm TiB2 and Ti in solid solution [1]. Table 1. Base alloy compositions (wt%) Si
Fe
Mg
Zn
Ti
Ni
Pb
Sn
Ca
B
Zr
V
Ga
Al
0.0753
0.0705
4.5252
0.0034
0.0173
0.0031
0.0021
0.0004
0.0004
0.0030
0.0017
0.0059
0.0087
95.2837
For RS-material the same alloy is used except that 1wt% Ag is added. Silver is selected as it may interact with Magnesium and form particles for strengthening or remain in solid solution. The Al4.5Mg is remelted in a graphite crucible and cast as rods with 40-44 mm in diameter. Then Al4.5Mg1.0Ag is alloyed by adding silver at 720°C and cast in a graphite crucible with an inner diameter of 40mm. 2.2. Rapid solidification, compacting and co-extrusion The rapid solidification device used is a laboratory scale melt spinning machine at NTNU/SINTEF. The working zone is shown in Figure 1a. The casting alloys are heated in a closed crucible by induction heating until melting at
Xiang Ma et al. / Procedia Engineering 207 (2017) 413–418 X. Ma / Procedia Engineering 00 (2017) 000–000
415 3
720°C. The material is kept in an argon atmosphere during heating. The temperature evolution of the crucible during this operation is shown in Figure 1b. The heating effect is increased in steps and about 4 kW is used to melt aluminium. The measured temperature dropped from 720°C to 660°C during the melting as the material obtains a better contact with the crucible wall (indicating by an purple arrow). The melt is kept 15 minutes at 720°C. Then a stream of melt is poured on the top of the rapid spinning wheel. The spinning wheel is continuously cooled internally by water so the melt is rapidly solidified. The rotating velocity is around 500rpm. A 0.5kg melt is rapidly solidified in two and a half minutes. An example of RS ribbons is shown in Figure 2a. Measurement of the ribbons shows that they are 1525μm thick with an average of about 19μm. The ribbons are about 5mm wide and several cm long (Figure 2b). The ribbons are cut in small pieces and compacted into a solid ring shape (Figure 2b).
Temperature (°C)
700
Temperature Power
4.5 4.0 3.5
600
3.0
500
2.5
400
2.0
300
1.5
200
1.0
100
0.5
0
0 10 20 30 40 50 60 70 80 90 100
Power (kW)
800
0.0
Time (min) (a)
(b)
Figure 1. Rapid solidification device (a) and the melting and power curves (b)
(a)
(b)
Figure 2. A large number of RS ribbons after rapid solidification of Al-4.5Mg-1.0Ag (a) and a metal ring compacted from the RS ribbons (b).
The co-extrusion is carried out by a 500 ton vertical press at SINTEF Raufoss Manufacturing. The extrusion device during operation is shown in Figure 3a. The base material billet is 125mm long with a diameter of 41mm. The RS material is 25mm long, with outer and inner diameters of 41 and 16mm, respectively. The base Al is put on the top of the RS Al, and both are pressed through a die with a diameter of 12mm. The container and the punch are heated up to temperatures of 440 and 250C respectively. The billets are co-extruded at temperature of 480C with an extrusion speed of 2.5mm/s. A typical load versus time curve is shown in Figure 3b with a maximum load of 140 ton recorded. Co-extrusion is performed successfully to generate a hybrid bar with a smooth RS surface layer.
Xiang Ma et al. / Procedia Engineering 207 (2017) 413–418 X. Ma / Procedia Engineering 00 (2017) 000–000
416 4
200 180
Extrusion force (Ton)
160 140 120 100 80 60 40 20 0
(a)
0
10
20
30
40
50
Time (sec)
60
70
80
(b)
Figure 3. Press equipment for co-extrusion (a) and a typical loadtime curve (b)
3. Analysis of RS material and co-extruded material 3.1. Microstructure of RS materials and co-extruded materials An optical image of the RS ribbons is shown in Figure 4a. The materials contain roundish particles with the size 0.10.5μm in most ribbons. The side with the straight line border has been solidified towards the cooled wheel, while the air-cooled side has a more wavy border. Some particles up to 1.5μm are found. The anodized cross section is shown in Figure 4b. These show that the side cooled by the wheel has recrystallized and has some grains of the order of 80-90μm, while the grain on the other side are only about 10μm. The figure also show the white etched areas of particles, indicating that these particles are on the side cooled by air. When the Al-4.5Mg material is coextruded with the RS material, a thin layer of RS-material is found on the surface of the extruded bar. The thickness of the RS surface layer is much larger in the beginning of the extrusion, compared with later stages. This RS material contains a high number of small dispersoids less than 1μm in diameter which are shown both in the optical and anodized images (white spots are etched particles) in Figure 5.
(a)
(b)
Figure 4. Optical image of the cross section of a RS ribbon containing small particles (a) and it's anodized cross sectional image (b).
When the material Al-4.5Mg is coextruded with the RS-material, a thin layer of RS-material is found on the surface of the extruded bar. The thickness of the RS surface layer is much larger in the beginning of the extrusion, compared with later stages. This RS material contains a high number of small dispersoids less than 1μm in diameter which are shown both in the optical and anodized images (white spots are etched particles) in Figure 5.
Xiang Ma et al. / Procedia Engineering 207 (2017) 413–418 X. Ma / Procedia Engineering 00 (2017) 000–000
(a)
417 5
(b)
Figure 5. Optical image (a) and anodized image (b) of a cross section of co-extruded bar with RS Al on the surface and Al-4.5Mg at the centre.
3.2. EDS analysis of RS ribbons and co-extruded materials Samples of RS ribbons and co-extruded material are polished and analyzed optically and by using SEM equipped with EDS for chemical analysis of the microstructures. The particles are so small that all analyses are a mixture of matrix with the particle in view. Therefore we analyze a series of the same phase to deduce what phase is in focus. Table 2. Analysis of elements in solid solution in RS ribbons No of analysis 1 9
wt% Mg 5.85 6.07
wt% Al 93.27 92.81
wt% Ag 0.88 1.12
Table 3. Analysis of particles in RS-materials in co-extruded material Size (m) 0.7 04 0.6 0.5 Matrix
wt%Mg wt%Al wt%Ag Volume% particle* 8.5 89.1 2.4 9.9 8.3 89.7 2.0 9.3 10.3 86.2 3.6 15.1 11.6 84.3 4.1 18.9 5.1 94.87 0.12 *The estimated percentage of the analyzed volume that is the AlAgMg particle
(a)
(b)
Figure 6. SEM images of a RS ribbon (a) and a RS surface layer in extruded samples (b).
The RS ribbon is analysed after solidification from a SEM image (Figure 6a), and the result is summarized in Table 2. The measured values are probably slightly high. Figure 6b is a SEM image from a co-extruded sample. According
Xiang Ma et al. / Procedia Engineering 207 (2017) 413–418 X. Ma / Procedia Engineering 00 (2017) 000–000
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to the ternary phase diagram of Al-Mg-Ag [1], the particles formed in our material are (Al, Ag)49Mg32. Assuming that this phase is present, the concentration of Mg is 39.5wt%. Then our analysis given in Table 3 shows that the concentration of silver in the particles is 21.9±1.4wt%. Thus the composition of the T-phase is close to Al31Ag17Mg32 (38.6wt%Al21.9wt%Ag39.5wt%Mg). The Tphase is reported to be cubic with a lattice parameter a=1.416nm. The metastable version is reported to strengthen Al–10wt%Mg–0.5wt%Ag at 240C [6]. Since the contents of Mg and Ag are higher in RS ribbons, some precipitation must have taken place during extrusion. We also detect some impurities in the RS material, namely Si-particles, and a few Al–Fe–Si particles, probably Al4Si2Fe. 3.3. Hardness of co-extruded materials The Vickers hardness distribution versus the positions in the co-extruded rod is shown in Figure 7a. The surface layer is harder than the base metal. The co-extruded material is then annealed at 160°C until 120 hours, after solution treatment in two steps at 400°C and 450°C. Figure 7b shows that the RS-material on the surface hardens higher than 85HV from the initial 65HV. It will be more if the material is hardened at a lower temperature that is 100 to 120°C. 90
74 85
70
68
66 1 2 3 4 5 6 7 8. . .
12
Vickers Hardness (HV)
Vickers hardness
72
Series1 Series2 Series3 Series4 Series5 Series6 Surface layer boundary Average
64
62
0
(a)
1
2
3
4
RS Al-4,5Mg-1Ag surface material
80
Al-4,5Mg base material
75
Average RS surface Average base
70
65
60
5
6
Position
7
8
9
10
11
12
0.1
1
10
100
1000
Annealing time (hour)]
(b)
Figure 7. Vickers hardness as a function of the position in the co-extruded rod (a) and after annealing (b).
Conclusions A laboratory scale rapid solidification device is used to produce RS-material of Al4.5Mg1.0Ag alloy. Coextrusion of this RS alloy with a base Al rod made of an Al4.5Mg can make a dual Al rod with superior RS surface layer, i.e., improved mechanical strength. Annealing of co-extruded rod with RS surface layer at 160C even give an increase in hardness of 30%. The microstructures of rapid solidified Al in co-extruded rod consist of small grains (50µm) and some small particles (0.11µm), mostly Al4Fe2Si and Si particles. Acknowledgements This work is sponsored by Hydro's fund on "Production of a dual Al alloy with distinguished surface properties". References [1] G. Petzow, G. Effenberg, Ternary Alloys: Volumes 13, VCH Publishers, New York, 19891990. [2] T.B. Massalski, Binary Alloy Phase Diagrams: Volume 1, 2nd ed., ASM International, Materials Park, Ohio, 1990. [3] E.J. Lavernia, T.S. Srivatsan, The rapid solidification processing of materials: science, principles, technology, advances, and applications, J. Mater. Sci., 45(2) (2009) 287325. [4] I. Johansen, H.J. Roven, Mechanical properties of a rapidly solidified AlSiNiMn alloy, Mater. Sci. Eng. A, 179 (1994) 605608. [5] I. Johansen, Properties, microstructure and modelling of a RS Aluminium Alloy, Norwegian Institute of Technology, Trondheim, PhD thesis, 1995. [6] M. Kubota, J.F. Nie, B.C. Muddle, Characterisation of Quasicrystalline Particles in an Isothermally Aged Al10Mg0.5Ag (mass%) Alloy, Materials Transactions, 46(6) (2005) 1278-1287.
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Available online at www.sciencedirect.com Procedia Engineering Engineering 00 00 (2017) (2017) 000–000 000–000 Procedia
ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Engineering 207 (2017) 413–418
International Conference on the Technology of Plasticity, ICTP 2017, 17-22 September 2017, Cambridge, United Kingdom
Co-extrusion of Dual Aluminum Alloys with Special Surface Properties a a b c d Xiang Maa*, Christian J. Simensena, Rune Østhusb, Wilhelm Dallc, Harald Kalagerd, Hans J. Rovendd, Leigang Wangee SINTEF SINTEF Materials Materials and and Chemistry, Chemistry, P.O.Box P.O.Box 124, 124, Blindern, Blindern, 0314 0314 Oslo, Oslo, Norway Norway SINTEF Raufoss Raufoss Manufacturing Manufacturing AS, AS, P.O.Box P.O.Box 163, 163, Raufoss, Raufoss, 2831 2831 Raufoss, Raufoss, Norway Norway SINTEF cc SINTEF SINTEF Materials Materials and and Chemistry, Chemistry, P.O. P.O. Box Box 4760, 4760, Sluppen, Sluppen, 7465 7465 Trondheim, Trondheim, Norway Norway ddDepartment of Materials Science and Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway Department of Materials Science and Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway ee School School of of Materials Materials Science Science and and Engineering, Engineering, Jiangsu Jiangsu University, University, Zhenjiang Zhenjiang 212013, 212013, China China a a
b b
Abstract Abstract Co-extrusion Co-extrusion method method is is used used for for production production of of aa dual dual Aluminum Aluminum rod. rod. The The surface surface layer layer material material for for co-extrusion co-extrusion is is prepared prepared by by rapid solidification process. The alloys Al4.5Mg1.0Ag (wt%) and Al4.5Mg are selected as the surface and the bulk rapid solidification process. The alloys Al4.5Mg1.0Ag (wt%) and Al4.5Mg are selected as the surface and the bulk materials, materials, respectively, and and are are co-extruded co-extruded at at high high temperature temperature range range (450480C). (450480C). The The microstructures microstructures of of rapid rapid solidified solidified Al Al in in co-extruded co-extruded respectively, rod consist consist of of small small grains grains (50µm) (50µm) and and some some small small particles particles (0.11µm). (0.11µm). A A proper proper annealing annealing on on the the extruded extruded rod rod increases increases the the rod surface surface hardness hardness more more than than 30%. 30%. Since Since the the co-extruded co-extruded material material contains contains small small T-phase T-phase particles, particles, this this increase increase in in hardness hardness indicates indicates precipitation precipitation of of aa metastable metastable MgAg MgAg phase phase or or aa MgAgAl MgAgAl phase phase at at 160C 160C during during annealing. annealing. © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. © © 2017 The Authors. Published by Elsevier Ltd. the scientific committee of the International Conference on the Technology Peer-review under responsibility of Peer-review under under responsibility responsibility of of the Peer-review scientific committee of the International Conference on the Technology of Plasticity. of Plasticity.. Keywords: Rapid Rapid solidification; solidification; Co-extrusion; Co-extrusion; Aluminium Aluminium alloy; alloy; Silver. Silver. Keywords:
1. Introduction As a crucial engineering material, Aluminum alloys are increasingly used in the automotive and transport
* * Corresponding Corresponding author. author. Tel.: Tel.: +47-98243925; +47-98243925; fax: fax: +47-22067350. +47-22067350. E-mail address: address: [email protected] [email protected] E-mail 1877-7058 1877-7058 © © 2017 2017 The The Authors. Authors. Published Published by by Elsevier Elsevier Ltd. Ltd. Peer-review under under responsibility responsibility of of the scientific committee Peer-review Plasticity..
of the International Conference on the Technology of
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity. 10.1016/j.proeng.2017.10.797
Xiang Ma et al. / Procedia Engineering 207 (2017) 413–418 X. Ma / Procedia Engineering 00 (2017) 000–000
414 2
industries, which have become the fastest growing markets for Al suppliers. The conventional process route for production of Al products, such as extruded sections, tubes or forged products is DC (direct chilled) casting, followed by homogenization, extrusion, forging and age hardening. For high-alloyed materials, this process route has its limitations because the solidification during DC casting is so slow that the material generates large macro-segregations if the alloying content is above 5–10 wt% [1, 2]. An alternative to the conventional DC casting process for such alloys is the rapid solidification process [3]. With this process, it is possible to achieve a very small-scaled crystalline structure and a homogeneous microstructure even for high alloyed materials. These factors can contribute to significant improvement with regard to material properties, with high yield strength, excellent fatigue resistant properties, reasonable ductility, high wear resistance and low thermal expansion coefficient. Such materials therefore have a great potential for automotive, aerospace and defense applications. Various production techniques are used to produce rapid solidified (RS) material. Both melt spinning process and centrifuge melt spinning process are developed in SINTEF and NTNU [4, 5] for RS Al production. During the melt spinning process, liquid Al is poured onto a fast-rotating copper wheel, causing very rapid solidification and forming a very thin metal ribbon. Our previous investigations [4, 5] have shown that RS Al alloys with excellent fatigue resistant properties can be obtained with only small intermetallic particles. Excellent properties with high pitting corrosion resistance can also be made from Al materials even without particles. Alloying elements with a high solubility, such as magnesium, zinc, silver and to some extent manganese, copper and chromium, are highly desirable for such purpose. To improve the production efficiency of lightweight parts through the combination of multi-materials and forming technologies, this investigation aims to examine the possibility to combine the production of RS Al-material with coextrusion method for production of a dual Al rod with high strength and/or excellent corrosion resistant properties at the surface and a ductile alloy in the bulk. As the surface layer is expected to be thin, pure Al without the common impurities and more exotic elements like Ag, Sc etc. can be used in the RS material for making the surface layer. The commercial Al materials as the bulk alloy also should have a low content of impurities. In doing so, a process route through production of RS Al, compaction of RS Al ribbons, and co-extrusion of RS Al with base Al alloys is proposed. The first part in this paper focuses on alloying for Al RS and base metals, rapid solidification, compacting of the RS material and successive co-extrusion. The second part is the microstructure analysis by EDS and hardness measurement of the co-extruded material, and annealing of the co-extruded rod and subsequent analysis. 2. Experimental 2.1. Alloying The base material is Al-4.5wt%Mg produced in Hydro Aluminium at Sunndal Verk. The compositions are determined by emission spectrometer. The main result is seen in Table 1. The material is grain refined with about 66 ppm borides, and is also expected to be refined by 64 ppm TiB2 and Ti in solid solution [1]. Table 1. Base alloy compositions (wt%) Si
Fe
Mg
Zn
Ti
Ni
Pb
Sn
Ca
B
Zr
V
Ga
Al
0.0753
0.0705
4.5252
0.0034
0.0173
0.0031
0.0021
0.0004
0.0004
0.0030
0.0017
0.0059
0.0087
95.2837
For RS-material the same alloy is used except that 1wt% Ag is added. Silver is selected as it may interact with Magnesium and form particles for strengthening or remain in solid solution. The Al4.5Mg is remelted in a graphite crucible and cast as rods with 40-44 mm in diameter. Then Al4.5Mg1.0Ag is alloyed by adding silver at 720°C and cast in a graphite crucible with an inner diameter of 40mm. 2.2. Rapid solidification, compacting and co-extrusion The rapid solidification device used is a laboratory scale melt spinning machine at NTNU/SINTEF. The working zone is shown in Figure 1a. The casting alloys are heated in a closed crucible by induction heating until melting at
Xiang Ma et al. / Procedia Engineering 207 (2017) 413–418 X. Ma / Procedia Engineering 00 (2017) 000–000
415 3
720°C. The material is kept in an argon atmosphere during heating. The temperature evolution of the crucible during this operation is shown in Figure 1b. The heating effect is increased in steps and about 4 kW is used to melt aluminium. The measured temperature dropped from 720°C to 660°C during the melting as the material obtains a better contact with the crucible wall (indicating by an purple arrow). The melt is kept 15 minutes at 720°C. Then a stream of melt is poured on the top of the rapid spinning wheel. The spinning wheel is continuously cooled internally by water so the melt is rapidly solidified. The rotating velocity is around 500rpm. A 0.5kg melt is rapidly solidified in two and a half minutes. An example of RS ribbons is shown in Figure 2a. Measurement of the ribbons shows that they are 1525μm thick with an average of about 19μm. The ribbons are about 5mm wide and several cm long (Figure 2b). The ribbons are cut in small pieces and compacted into a solid ring shape (Figure 2b).
Temperature (°C)
700
Temperature Power
4.5 4.0 3.5
600
3.0
500
2.5
400
2.0
300
1.5
200
1.0
100
0.5
0
0 10 20 30 40 50 60 70 80 90 100
Power (kW)
800
0.0
Time (min) (a)
(b)
Figure 1. Rapid solidification device (a) and the melting and power curves (b)
(a)
(b)
Figure 2. A large number of RS ribbons after rapid solidification of Al-4.5Mg-1.0Ag (a) and a metal ring compacted from the RS ribbons (b).
The co-extrusion is carried out by a 500 ton vertical press at SINTEF Raufoss Manufacturing. The extrusion device during operation is shown in Figure 3a. The base material billet is 125mm long with a diameter of 41mm. The RS material is 25mm long, with outer and inner diameters of 41 and 16mm, respectively. The base Al is put on the top of the RS Al, and both are pressed through a die with a diameter of 12mm. The container and the punch are heated up to temperatures of 440 and 250C respectively. The billets are co-extruded at temperature of 480C with an extrusion speed of 2.5mm/s. A typical load versus time curve is shown in Figure 3b with a maximum load of 140 ton recorded. Co-extrusion is performed successfully to generate a hybrid bar with a smooth RS surface layer.
Xiang Ma et al. / Procedia Engineering 207 (2017) 413–418 X. Ma / Procedia Engineering 00 (2017) 000–000
416 4
200 180
Extrusion force (Ton)
160 140 120 100 80 60 40 20 0
(a)
0
10
20
30
40
50
Time (sec)
60
70
80
(b)
Figure 3. Press equipment for co-extrusion (a) and a typical loadtime curve (b)
3. Analysis of RS material and co-extruded material 3.1. Microstructure of RS materials and co-extruded materials An optical image of the RS ribbons is shown in Figure 4a. The materials contain roundish particles with the size 0.10.5μm in most ribbons. The side with the straight line border has been solidified towards the cooled wheel, while the air-cooled side has a more wavy border. Some particles up to 1.5μm are found. The anodized cross section is shown in Figure 4b. These show that the side cooled by the wheel has recrystallized and has some grains of the order of 80-90μm, while the grain on the other side are only about 10μm. The figure also show the white etched areas of particles, indicating that these particles are on the side cooled by air. When the Al-4.5Mg material is coextruded with the RS material, a thin layer of RS-material is found on the surface of the extruded bar. The thickness of the RS surface layer is much larger in the beginning of the extrusion, compared with later stages. This RS material contains a high number of small dispersoids less than 1μm in diameter which are shown both in the optical and anodized images (white spots are etched particles) in Figure 5.
(a)
(b)
Figure 4. Optical image of the cross section of a RS ribbon containing small particles (a) and it's anodized cross sectional image (b).
When the material Al-4.5Mg is coextruded with the RS-material, a thin layer of RS-material is found on the surface of the extruded bar. The thickness of the RS surface layer is much larger in the beginning of the extrusion, compared with later stages. This RS material contains a high number of small dispersoids less than 1μm in diameter which are shown both in the optical and anodized images (white spots are etched particles) in Figure 5.
Xiang Ma et al. / Procedia Engineering 207 (2017) 413–418 X. Ma / Procedia Engineering 00 (2017) 000–000
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Figure 5. Optical image (a) and anodized image (b) of a cross section of co-extruded bar with RS Al on the surface and Al-4.5Mg at the centre.
3.2. EDS analysis of RS ribbons and co-extruded materials Samples of RS ribbons and co-extruded material are polished and analyzed optically and by using SEM equipped with EDS for chemical analysis of the microstructures. The particles are so small that all analyses are a mixture of matrix with the particle in view. Therefore we analyze a series of the same phase to deduce what phase is in focus. Table 2. Analysis of elements in solid solution in RS ribbons No of analysis 1 9
wt% Mg 5.85 6.07
wt% Al 93.27 92.81
wt% Ag 0.88 1.12
Table 3. Analysis of particles in RS-materials in co-extruded material Size (m) 0.7 04 0.6 0.5 Matrix
wt%Mg wt%Al wt%Ag Volume% particle* 8.5 89.1 2.4 9.9 8.3 89.7 2.0 9.3 10.3 86.2 3.6 15.1 11.6 84.3 4.1 18.9 5.1 94.87 0.12 *The estimated percentage of the analyzed volume that is the AlAgMg particle
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Figure 6. SEM images of a RS ribbon (a) and a RS surface layer in extruded samples (b).
The RS ribbon is analysed after solidification from a SEM image (Figure 6a), and the result is summarized in Table 2. The measured values are probably slightly high. Figure 6b is a SEM image from a co-extruded sample. According
Xiang Ma et al. / Procedia Engineering 207 (2017) 413–418 X. Ma / Procedia Engineering 00 (2017) 000–000
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to the ternary phase diagram of Al-Mg-Ag [1], the particles formed in our material are (Al, Ag)49Mg32. Assuming that this phase is present, the concentration of Mg is 39.5wt%. Then our analysis given in Table 3 shows that the concentration of silver in the particles is 21.9±1.4wt%. Thus the composition of the T-phase is close to Al31Ag17Mg32 (38.6wt%Al21.9wt%Ag39.5wt%Mg). The Tphase is reported to be cubic with a lattice parameter a=1.416nm. The metastable version is reported to strengthen Al–10wt%Mg–0.5wt%Ag at 240C [6]. Since the contents of Mg and Ag are higher in RS ribbons, some precipitation must have taken place during extrusion. We also detect some impurities in the RS material, namely Si-particles, and a few Al–Fe–Si particles, probably Al4Si2Fe. 3.3. Hardness of co-extruded materials The Vickers hardness distribution versus the positions in the co-extruded rod is shown in Figure 7a. The surface layer is harder than the base metal. The co-extruded material is then annealed at 160°C until 120 hours, after solution treatment in two steps at 400°C and 450°C. Figure 7b shows that the RS-material on the surface hardens higher than 85HV from the initial 65HV. It will be more if the material is hardened at a lower temperature that is 100 to 120°C. 90
74 85
70
68
66 1 2 3 4 5 6 7 8. . .
12
Vickers Hardness (HV)
Vickers hardness
72
Series1 Series2 Series3 Series4 Series5 Series6 Surface layer boundary Average
64
62
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RS Al-4,5Mg-1Ag surface material
80
Al-4,5Mg base material
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Average RS surface Average base
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65
60
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6
Position
7
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Figure 7. Vickers hardness as a function of the position in the co-extruded rod (a) and after annealing (b).
Conclusions A laboratory scale rapid solidification device is used to produce RS-material of Al4.5Mg1.0Ag alloy. Coextrusion of this RS alloy with a base Al rod made of an Al4.5Mg can make a dual Al rod with superior RS surface layer, i.e., improved mechanical strength. Annealing of co-extruded rod with RS surface layer at 160C even give an increase in hardness of 30%. The microstructures of rapid solidified Al in co-extruded rod consist of small grains (50µm) and some small particles (0.11µm), mostly Al4Fe2Si and Si particles. Acknowledgements This work is sponsored by Hydro's fund on "Production of a dual Al alloy with distinguished surface properties". References [1] G. Petzow, G. Effenberg, Ternary Alloys: Volumes 13, VCH Publishers, New York, 19891990. [2] T.B. Massalski, Binary Alloy Phase Diagrams: Volume 1, 2nd ed., ASM International, Materials Park, Ohio, 1990. [3] E.J. Lavernia, T.S. Srivatsan, The rapid solidification processing of materials: science, principles, technology, advances, and applications, J. Mater. Sci., 45(2) (2009) 287325. [4] I. Johansen, H.J. Roven, Mechanical properties of a rapidly solidified AlSiNiMn alloy, Mater. Sci. Eng. A, 179 (1994) 605608. [5] I. Johansen, Properties, microstructure and modelling of a RS Aluminium Alloy, Norwegian Institute of Technology, Trondheim, PhD thesis, 1995. [6] M. Kubota, J.F. Nie, B.C. Muddle, Characterisation of Quasicrystalline Particles in an Isothermally Aged Al10Mg0.5Ag (mass%) Alloy, Materials Transactions, 46(6) (2005) 1278-1287.