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Mechanical properties of a powder metallurgically processed Mg–5Y–6Re alloy
Materials Science and Engineering A293 (2000) 15 – 18 www.elsevier.com/locate/msea
Mechanical properties of a powder metallurgically processed Mg–5Y–6Re alloy K. Nakashima a, H. Iwasaki a,*, T. Mori a, M. Mabuchi b, M. Nakamura b, T. Asahina b a
College of Engineering, Department of Materials Science and Engineering, Himeji Institute of Technology, Shosha, Himeji, Hyogo 671 -2201, Japan b National Industrial Research Institute of Nagoya, Hirate-cho, Kita-ku, Nagoya 462 -8510, Japan Received 21 April 2000; received in revised form 5 June 2000
Abstract A rapidly solidified powder of Mg–5 wt.%Y–6 wt.%Re alloy (chemical composition: Mg – 4.74 wt.%Y – 3.36 wt.%Nd–1.76 wt.%Pr–0.71 wt.%Ce) was extruded at 573 K with a reduction ratio of 20:1 in a vacuum. Mechanical properties of the P/M Mg alloy were investigated by velocity-constant tensile tests at room temperature to 773 K. The powder metallurgy Mg alloy had a mean grain size of 0.5 mm. The alloy exhibited a high strength of 536 MPa at room temperature and superplastic behavior at a high strain rate of 1.7×10 − 1 s − 1 at 773 K. These characteristic mechanical properties might be attributed to the sub-micron grained structure. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Powder processing; Magnesium–rare earth alloy; Mechanical properties; Superplasticity; Fine-grained structure
1. Introduction Magnesium alloys have a high potential as structural light materials because of their low density. Furthermore, Mg resources are abundant, and also Mg products can be recycled more easily compared to polymers. Recently, it has been reported that the mechanical properties of Mg alloys significantly depend on the grain size [1]. Mg – Al – Zn and Mg – Zn – Zr alloys processed by a powder metallurgy (P/M) method exhibited a high strength of greater than 400 MPa at room temperature [2,3] and superplasticity in the high strain rate range of 10 − 2 – 10 − 1 s − 1 at 523 – 673 K [4]. The high strength and high strain rate superplasticity of the P/M Mg–Al–Zn and Mg – Zn – Zr alloys are attributed to the small grain sizes of about 1 – 3 mm. It is important to attain high creep resistance and
* Corresponding author. Tel.: +81-792-674908; fax: + 81-792674908. E-mail address: [email protected] (H. Iwasaki).
high strength at elevated temperatures as well as high strength at room temperature and high strain rate superplasticity in order to increase the applications of Mg alloys. Creep resistance of Mg can be improved by the addition of Y and Re (Re: rare earth metals) [5–7]. Recently, Mohri et al. [8] extruded the cast Mg–4Y– 3Re alloy and investigated the mechanical properties of the extruded Mg–Y–Re alloy. They showed that the extruded Mg–Y–Re alloy exhibited a high strength of greater than 300 MPa to a high temperature of 473 K and a large elongation of 1274% at 673 K and 2 ×10 − 3 s − 1. These excellent mechanical properties of the extruded Mg–Y–Re alloy are attributed to the small grain size of 1.5 mm and the uniform distribution of the fine precipitates [8]. In the present investigation, a Mg–5 wt.%Y–6 wt.%Re alloy was processed by a powder metallurgy method in order to attain a smaller grain size. The mechanical properties of the P/M Mg–Y–Re alloy are investigated by tensile tests from room temperature to 773 K.
0921-5093/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 0 ) 0 1 2 4 1 - 7
K. Nakashima et al. / Materials Science and Engineering A293 (2000) 15–18
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2. Experimental procedures A rapidly solidified Mg – 5 wt.%Y – 6 wt.%Re powder (chemical composition: Mg – 4.74 wt.%Y–3.36
wt.%Nd–1.76 wt.%Pr–0.71 wt.%Ce) was prepared (Fig. 1). The powder was extruded at 573 K with a reduction ratio of 20:1 in a vacuum. Tensile specimens were machined from the as-extruded bar. The tensile specimens had a gage length of 10 mm and a gage diameter of 2.5 mm. Constant velocity tensile tests were carried out from room temperature to 773 K and at a constant initial strain rate of 1.7× 10 − 3 s − 1 in air. In addition constant velocity tensile tests were carried out at 673 and 773 K with 1.7× 10 − 3 –1.7×10 − 1 s − 1 in air to investigate the superplastic behavior. The tensile axis was made parallel to the extrusion direction. The specimens required 1.8× 103 s to equilibrate at the test temperature prior to the initiation of straining. The temperature variation during the tensile tests was not more than 91 K. The microstructures of the grains and precipitates were investigated using a transmission electron microscope.
Fig. 1. Rapidly solidified Mg–5 wt.%Y–6 wt.%Re powder.
3. Results and discussion
Fig. 2. A transmission electron micrograph of the P/M Mg – Y – Re alloy.
A transmission electron micrograph of the P/M Mg– Y–Re alloy is shown in Fig. 2. The grains were almost equiaxed. The grain size of the P/M Mg–Y–Re alloy was 0.5 mm. Mohri et al. [8] showed that grain refinement of the cast Mg–4Y–3Re alloy was attained by hot extrusion and the extruded Mg–Y–Re alloy showed a small grain size of 1.5 mm. However, the grain size of the P/M Mg–Y–Re alloy was much smaller than that of the extruded Mg–Y–Re alloy. A very small grain size of 0.5 mm was attained by the powder metallurgical method. Precipitates of the P/M Mg–Y–Re alloy are shown in Fig. 3. The morphology of the precipitates was plate-like, suggesting that the precipitates were b%% [9]. The mean values of the precipitate size, a, and the precipitate center-to-center spacing, L, were 0.075 and 0.286 mm, respectively. The results of the tensile tests at room temperature of the Mg–Y–Re alloys are listed in Table 1. The P/M Mg–Y–Re alloy exhibited a high strength of 536 MPa and a high 0.2% proof stress of 528 MPa. The high strength of the P/M Mg–Y–Re alloy may be attributed to the dislocation–particle interaction by the Orowan process and the small grain size. An increase in the yield stress due to the Orowan process, Dsorowan, can be given by [10,11]: Dsorowan =
Fig. 3. Precipitates in the P/M Mg–Y–Re alloy.
AEMb D ln + B 4p(1+ n)l ro
n
(1)
where A= 1/(1 + n) and B=0.6 for screw dislocations and A= 1 and B= 0.7 for edge dislocations, E is Young’s modulus, M is the Taylor factor, b is the Burgers vector, n is Poisson’s ratio, l is the interparticle
K. Nakashima et al. / Materials Science and Engineering A293 (2000) 15–18
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Table 1 Tensile properties at room temperature of Mg–Y–Re alloys Materials P/M Mg–5Y–6Re Solution treated Mg–4Y–3Rea Peak aged Mg–4Y–3Rea Extruded Mg–4Y–3Rea,b a b
Ultimate tensile strength (MPa)
0.2% Proof stress (MPa)
536 233 301 320
528 141 178 208
Elongation to failure (%) 2 16 6 20
Ref. [8]. Extrusion at 673 K.
spacing, D is the harmonic mean of l and a, and ro is the inner cutoff radius of the dislocation (= b–3b). From Eq. (1) an increase in the yield stress due to the Orowan process in the P/M Mg – Y – Re alloy is estimated to be 250 MPa (ro =b) and 207 MPa (ro = 3b) for screw dislocations, and 178 MPa (ro =b) and 148 MPa (ro = 3b) for edge dislocations, where E= 44.8 GPa [12], M=6.5 [13], b =3.21 ×10 − 10 m [14] and n = 0.3. The influence of the grain size on the yield stress can be estimated using a standard Hall – Petch equation of the form [15]: DsGS = K/d 1/2
the high strain rate range 1.7× 10 − 3 –1.7×10 − 1 s − 1 at 673 and 773 K. The results are listed in Table 2. A large elongation of 346% was obtained at the high strain rate of 1.7× 10 − 1 s − 1 at 773 K. The superplastic strain rate of 1.7× 10 − 1 s − 1 in the P/M Mg–Y–Re alloy is much higher than that of 2× 10 − 3 s − 1 in the
(2)
where DsGS is the increase in yield stress due to grain refinement, K is a constant and d is the grain size. From Eq. (2) an increase in the yield stress due to grain refinement in the P/M Mg – Y – Re alloy is estimated to be 297 MPa, assuming that the value of K of the Mg –Y –Re alloys is the same as that of the AZ91 Mg alloys ( =210 MPa mm − 1/2 [16]). This suggests that the contribution of the fine-grain strengthening mechanism to the high strength of the P/M Mg – Y – Re alloy is relatively large. The variations in the ultimate tensile strength (top figure) and elongation to failure (bottom figure) as a function of testing temperature in the Mg – Y – Re alloys are shown in Fig. 4. The P/M Mg – Y – Re alloy exhibited a much higher strength than the cast and the extruded Mg–Y – Re alloys up to the high temperature of 473 K. In particular, the P/M Mg – Y – Re alloy showed a high strength of more than 400 MPa even at 473 K. However, the P/M Mg – Y – Re alloy showed a rapid decrease in strength at 573 K and the strength of the P/M Mg–Y – Re alloy was almost the same as or lower than those of the cast and the extruded Mg–Y– Re alloys in the temperature range greater than 573 K. The extruded Mg – Y – Re alloy showed superplastic behavior for a large elongation of 1274% at 673 K [8]. However, the elongation of the P/M Mg – Y – Re alloy at 673 K was 96%, despite the very small grain size of 0.5 mm. The superplastic strain rate range tends to increase with decreasing grain size [17]. Hence, superplastic behavior of the P/M Mg – Y – Re alloy was investigated in
Fig. 4. The variations in ultimate tensile strength (top figure) and elongation to failure (bottom figure) as a function of testing temperature in Mg – Y – Re alloys. Table 2 The superplastic properties of the P/M Mg–Y–Re alloy Temperature (K)
Strain rate (s−1)
Flow stressa (MPa)
673 673 673 773 773
1.7×10−3 1.7×10−2 1.7×10−1 1.7×10−3 1.7×10−1
16.7 27.2 39.8 4.7 17.1
a
The true stress at o =0.1.
Elongation (%) 96 173 256 129 346
18
K. Nakashima et al. / Materials Science and Engineering A293 (2000) 15–18
extruded Mg–Y – Re alloy [8]. This is attributed to the significantly smaller grain size of 0.5 mm of the P/M Mg –Y –Re alloy. Grain growth often occurs during superplastic deformation. Grain growth may cause a large decrease in strength of the post-deformation P/M Mg – Y – Re alloy because a contribution of the fine-grain strengthening mechanism to the high strength of the P/M Mg –Y–Re alloy is relatively large. However, probably, grain growth in the P/M Mg – Y – Re alloy is not large, compared to conventional superplastic materials, because the superplastic deformation time for the P/M Mg–Y– Re alloy is much shorter than that for conventional superplastic materials. Hence, a decrease in strength for the post-deformation P/M Mg – Y – Re alloy may not be large. Further research is needed to investigate effects of microstructural evolution on the post-deformation properties of the P/M Mg – Y – Re alloy.
4. Summary The P/M Mg – 5Y – 6Re alloy exhibited a high strength of 536 MPa at room temperature and superplastic behavior at a high strain rate of 1.7 × 10 − 1 s − 1 at 773 K. These excellent mechanical properties of the P/M Mg–Y –Re alloy are attributed to the very small grain size of 0.5 mm.
.
References [1] K. Kubota, M. Mabuchi, K. Higashi, J. Mater. Sci. 34 (1999) 2255. [2] H. Iwasaki, K. Yanase, T. Mori, M. Mabuchi, K. Higashi, J. Jpn. Soc. Powder Powder Metall. 43 (1996) 1350 (in Japanese). [3] M. Mabuchi, M. Nakamura, K. Higashi, in: B.L. Mordike, K.U. Kainer (Eds.), Magnesium Alloys and their Applications, Werkstoff-Informationsgesellshaft, Frankfurt, 1998, p. 91. [4] M. Mabuchi, T. Asahina, H. Iwasaki, K. Higashi, Mater. Sci. Technol. 13 (1997) 825. [5] T.E. Leontis, J. Met. 3 (1951) 987. [6] B.L. Mordike, W. Henning, in: C. Baker, G.W. Lorimer, W. Unsworth (Eds.), Magnesium Technology, The Institute of Metals, London, 1987, p. 54. [7] H. Karimzadeh, J.M. Worrall, R. Pilkington, G.W Lorimer, in: C. Baker, G.W. Lorimer, W. Unsworth (Eds.), Magnesium Technology, The Institute of Metals, London, 1987, p. 138. [8] T. Mohri, M. Mabuchi, N. Saito, M. Nakamura, Mater. Sci. Eng. A257 (1998) 287. [9] I.J. Polmear, Mater. Sci. Technol. 10 (1994) 1. [10] R.O. Scattergood, D. Bacon, Phil. Mag. A31 (1975) 179. [11] Y.H. Yeh, H. Nakashima, H. Kurishita, S. Goto, H. Yoshinaga, Mater. Trans. JIM 31 (1990) 284. [12] K. Ito, K. Shibata, J. Kaneko, in: Kouzou Zairyou-Kinzoku, Tokyo University Press, Tokyo, 1985, p. 138 (in Japanese). [13] R.W. Armstrong, I. Codd, R.M. Douthwaite, N.J. Petch, Phil. Mag. 7 (1962) 45. [14] H.J. Frost, M.F. Ashby, in: Deformation-Mechanism Maps, Pergamon, Oxford, 1982, p. 44. [15] N.J. Petch, J. Iron Steel Inst. 174 (1953) 25. [16] G. Nussbaum, P. Sainfort, G. Regazzoni, H. Gjestland, Scrip. Metall. 23 (1989) 1079. [17] M. Mabuchi, K. Higashi, Phil. Mag. A74 (1996) 887.
Mechanical properties of a powder metallurgically processed Mg–5Y–6Re alloy K. Nakashima a, H. Iwasaki a,*, T. Mori a, M. Mabuchi b, M. Nakamura b, T. Asahina b a
College of Engineering, Department of Materials Science and Engineering, Himeji Institute of Technology, Shosha, Himeji, Hyogo 671 -2201, Japan b National Industrial Research Institute of Nagoya, Hirate-cho, Kita-ku, Nagoya 462 -8510, Japan Received 21 April 2000; received in revised form 5 June 2000
Abstract A rapidly solidified powder of Mg–5 wt.%Y–6 wt.%Re alloy (chemical composition: Mg – 4.74 wt.%Y – 3.36 wt.%Nd–1.76 wt.%Pr–0.71 wt.%Ce) was extruded at 573 K with a reduction ratio of 20:1 in a vacuum. Mechanical properties of the P/M Mg alloy were investigated by velocity-constant tensile tests at room temperature to 773 K. The powder metallurgy Mg alloy had a mean grain size of 0.5 mm. The alloy exhibited a high strength of 536 MPa at room temperature and superplastic behavior at a high strain rate of 1.7×10 − 1 s − 1 at 773 K. These characteristic mechanical properties might be attributed to the sub-micron grained structure. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Powder processing; Magnesium–rare earth alloy; Mechanical properties; Superplasticity; Fine-grained structure
1. Introduction Magnesium alloys have a high potential as structural light materials because of their low density. Furthermore, Mg resources are abundant, and also Mg products can be recycled more easily compared to polymers. Recently, it has been reported that the mechanical properties of Mg alloys significantly depend on the grain size [1]. Mg – Al – Zn and Mg – Zn – Zr alloys processed by a powder metallurgy (P/M) method exhibited a high strength of greater than 400 MPa at room temperature [2,3] and superplasticity in the high strain rate range of 10 − 2 – 10 − 1 s − 1 at 523 – 673 K [4]. The high strength and high strain rate superplasticity of the P/M Mg–Al–Zn and Mg – Zn – Zr alloys are attributed to the small grain sizes of about 1 – 3 mm. It is important to attain high creep resistance and
* Corresponding author. Tel.: +81-792-674908; fax: + 81-792674908. E-mail address: [email protected] (H. Iwasaki).
high strength at elevated temperatures as well as high strength at room temperature and high strain rate superplasticity in order to increase the applications of Mg alloys. Creep resistance of Mg can be improved by the addition of Y and Re (Re: rare earth metals) [5–7]. Recently, Mohri et al. [8] extruded the cast Mg–4Y– 3Re alloy and investigated the mechanical properties of the extruded Mg–Y–Re alloy. They showed that the extruded Mg–Y–Re alloy exhibited a high strength of greater than 300 MPa to a high temperature of 473 K and a large elongation of 1274% at 673 K and 2 ×10 − 3 s − 1. These excellent mechanical properties of the extruded Mg–Y–Re alloy are attributed to the small grain size of 1.5 mm and the uniform distribution of the fine precipitates [8]. In the present investigation, a Mg–5 wt.%Y–6 wt.%Re alloy was processed by a powder metallurgy method in order to attain a smaller grain size. The mechanical properties of the P/M Mg–Y–Re alloy are investigated by tensile tests from room temperature to 773 K.
0921-5093/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 0 ) 0 1 2 4 1 - 7
K. Nakashima et al. / Materials Science and Engineering A293 (2000) 15–18
16
2. Experimental procedures A rapidly solidified Mg – 5 wt.%Y – 6 wt.%Re powder (chemical composition: Mg – 4.74 wt.%Y–3.36
wt.%Nd–1.76 wt.%Pr–0.71 wt.%Ce) was prepared (Fig. 1). The powder was extruded at 573 K with a reduction ratio of 20:1 in a vacuum. Tensile specimens were machined from the as-extruded bar. The tensile specimens had a gage length of 10 mm and a gage diameter of 2.5 mm. Constant velocity tensile tests were carried out from room temperature to 773 K and at a constant initial strain rate of 1.7× 10 − 3 s − 1 in air. In addition constant velocity tensile tests were carried out at 673 and 773 K with 1.7× 10 − 3 –1.7×10 − 1 s − 1 in air to investigate the superplastic behavior. The tensile axis was made parallel to the extrusion direction. The specimens required 1.8× 103 s to equilibrate at the test temperature prior to the initiation of straining. The temperature variation during the tensile tests was not more than 91 K. The microstructures of the grains and precipitates were investigated using a transmission electron microscope.
Fig. 1. Rapidly solidified Mg–5 wt.%Y–6 wt.%Re powder.
3. Results and discussion
Fig. 2. A transmission electron micrograph of the P/M Mg – Y – Re alloy.
A transmission electron micrograph of the P/M Mg– Y–Re alloy is shown in Fig. 2. The grains were almost equiaxed. The grain size of the P/M Mg–Y–Re alloy was 0.5 mm. Mohri et al. [8] showed that grain refinement of the cast Mg–4Y–3Re alloy was attained by hot extrusion and the extruded Mg–Y–Re alloy showed a small grain size of 1.5 mm. However, the grain size of the P/M Mg–Y–Re alloy was much smaller than that of the extruded Mg–Y–Re alloy. A very small grain size of 0.5 mm was attained by the powder metallurgical method. Precipitates of the P/M Mg–Y–Re alloy are shown in Fig. 3. The morphology of the precipitates was plate-like, suggesting that the precipitates were b%% [9]. The mean values of the precipitate size, a, and the precipitate center-to-center spacing, L, were 0.075 and 0.286 mm, respectively. The results of the tensile tests at room temperature of the Mg–Y–Re alloys are listed in Table 1. The P/M Mg–Y–Re alloy exhibited a high strength of 536 MPa and a high 0.2% proof stress of 528 MPa. The high strength of the P/M Mg–Y–Re alloy may be attributed to the dislocation–particle interaction by the Orowan process and the small grain size. An increase in the yield stress due to the Orowan process, Dsorowan, can be given by [10,11]: Dsorowan =
Fig. 3. Precipitates in the P/M Mg–Y–Re alloy.
AEMb D ln + B 4p(1+ n)l ro
n
(1)
where A= 1/(1 + n) and B=0.6 for screw dislocations and A= 1 and B= 0.7 for edge dislocations, E is Young’s modulus, M is the Taylor factor, b is the Burgers vector, n is Poisson’s ratio, l is the interparticle
K. Nakashima et al. / Materials Science and Engineering A293 (2000) 15–18
17
Table 1 Tensile properties at room temperature of Mg–Y–Re alloys Materials P/M Mg–5Y–6Re Solution treated Mg–4Y–3Rea Peak aged Mg–4Y–3Rea Extruded Mg–4Y–3Rea,b a b
Ultimate tensile strength (MPa)
0.2% Proof stress (MPa)
536 233 301 320
528 141 178 208
Elongation to failure (%) 2 16 6 20
Ref. [8]. Extrusion at 673 K.
spacing, D is the harmonic mean of l and a, and ro is the inner cutoff radius of the dislocation (= b–3b). From Eq. (1) an increase in the yield stress due to the Orowan process in the P/M Mg – Y – Re alloy is estimated to be 250 MPa (ro =b) and 207 MPa (ro = 3b) for screw dislocations, and 178 MPa (ro =b) and 148 MPa (ro = 3b) for edge dislocations, where E= 44.8 GPa [12], M=6.5 [13], b =3.21 ×10 − 10 m [14] and n = 0.3. The influence of the grain size on the yield stress can be estimated using a standard Hall – Petch equation of the form [15]: DsGS = K/d 1/2
the high strain rate range 1.7× 10 − 3 –1.7×10 − 1 s − 1 at 673 and 773 K. The results are listed in Table 2. A large elongation of 346% was obtained at the high strain rate of 1.7× 10 − 1 s − 1 at 773 K. The superplastic strain rate of 1.7× 10 − 1 s − 1 in the P/M Mg–Y–Re alloy is much higher than that of 2× 10 − 3 s − 1 in the
(2)
where DsGS is the increase in yield stress due to grain refinement, K is a constant and d is the grain size. From Eq. (2) an increase in the yield stress due to grain refinement in the P/M Mg – Y – Re alloy is estimated to be 297 MPa, assuming that the value of K of the Mg –Y –Re alloys is the same as that of the AZ91 Mg alloys ( =210 MPa mm − 1/2 [16]). This suggests that the contribution of the fine-grain strengthening mechanism to the high strength of the P/M Mg – Y – Re alloy is relatively large. The variations in the ultimate tensile strength (top figure) and elongation to failure (bottom figure) as a function of testing temperature in the Mg – Y – Re alloys are shown in Fig. 4. The P/M Mg – Y – Re alloy exhibited a much higher strength than the cast and the extruded Mg–Y – Re alloys up to the high temperature of 473 K. In particular, the P/M Mg – Y – Re alloy showed a high strength of more than 400 MPa even at 473 K. However, the P/M Mg – Y – Re alloy showed a rapid decrease in strength at 573 K and the strength of the P/M Mg–Y – Re alloy was almost the same as or lower than those of the cast and the extruded Mg–Y– Re alloys in the temperature range greater than 573 K. The extruded Mg – Y – Re alloy showed superplastic behavior for a large elongation of 1274% at 673 K [8]. However, the elongation of the P/M Mg – Y – Re alloy at 673 K was 96%, despite the very small grain size of 0.5 mm. The superplastic strain rate range tends to increase with decreasing grain size [17]. Hence, superplastic behavior of the P/M Mg – Y – Re alloy was investigated in
Fig. 4. The variations in ultimate tensile strength (top figure) and elongation to failure (bottom figure) as a function of testing temperature in Mg – Y – Re alloys. Table 2 The superplastic properties of the P/M Mg–Y–Re alloy Temperature (K)
Strain rate (s−1)
Flow stressa (MPa)
673 673 673 773 773
1.7×10−3 1.7×10−2 1.7×10−1 1.7×10−3 1.7×10−1
16.7 27.2 39.8 4.7 17.1
a
The true stress at o =0.1.
Elongation (%) 96 173 256 129 346
18
K. Nakashima et al. / Materials Science and Engineering A293 (2000) 15–18
extruded Mg–Y – Re alloy [8]. This is attributed to the significantly smaller grain size of 0.5 mm of the P/M Mg –Y –Re alloy. Grain growth often occurs during superplastic deformation. Grain growth may cause a large decrease in strength of the post-deformation P/M Mg – Y – Re alloy because a contribution of the fine-grain strengthening mechanism to the high strength of the P/M Mg –Y–Re alloy is relatively large. However, probably, grain growth in the P/M Mg – Y – Re alloy is not large, compared to conventional superplastic materials, because the superplastic deformation time for the P/M Mg–Y– Re alloy is much shorter than that for conventional superplastic materials. Hence, a decrease in strength for the post-deformation P/M Mg – Y – Re alloy may not be large. Further research is needed to investigate effects of microstructural evolution on the post-deformation properties of the P/M Mg – Y – Re alloy.
4. Summary The P/M Mg – 5Y – 6Re alloy exhibited a high strength of 536 MPa at room temperature and superplastic behavior at a high strain rate of 1.7 × 10 − 1 s − 1 at 773 K. These excellent mechanical properties of the P/M Mg–Y –Re alloy are attributed to the very small grain size of 0.5 mm.
.
References [1] K. Kubota, M. Mabuchi, K. Higashi, J. Mater. Sci. 34 (1999) 2255. [2] H. Iwasaki, K. Yanase, T. Mori, M. Mabuchi, K. Higashi, J. Jpn. Soc. Powder Powder Metall. 43 (1996) 1350 (in Japanese). [3] M. Mabuchi, M. Nakamura, K. Higashi, in: B.L. Mordike, K.U. Kainer (Eds.), Magnesium Alloys and their Applications, Werkstoff-Informationsgesellshaft, Frankfurt, 1998, p. 91. [4] M. Mabuchi, T. Asahina, H. Iwasaki, K. Higashi, Mater. Sci. Technol. 13 (1997) 825. [5] T.E. Leontis, J. Met. 3 (1951) 987. [6] B.L. Mordike, W. Henning, in: C. Baker, G.W. Lorimer, W. Unsworth (Eds.), Magnesium Technology, The Institute of Metals, London, 1987, p. 54. [7] H. Karimzadeh, J.M. Worrall, R. Pilkington, G.W Lorimer, in: C. Baker, G.W. Lorimer, W. Unsworth (Eds.), Magnesium Technology, The Institute of Metals, London, 1987, p. 138. [8] T. Mohri, M. Mabuchi, N. Saito, M. Nakamura, Mater. Sci. Eng. A257 (1998) 287. [9] I.J. Polmear, Mater. Sci. Technol. 10 (1994) 1. [10] R.O. Scattergood, D. Bacon, Phil. Mag. A31 (1975) 179. [11] Y.H. Yeh, H. Nakashima, H. Kurishita, S. Goto, H. Yoshinaga, Mater. Trans. JIM 31 (1990) 284. [12] K. Ito, K. Shibata, J. Kaneko, in: Kouzou Zairyou-Kinzoku, Tokyo University Press, Tokyo, 1985, p. 138 (in Japanese). [13] R.W. Armstrong, I. Codd, R.M. Douthwaite, N.J. Petch, Phil. Mag. 7 (1962) 45. [14] H.J. Frost, M.F. Ashby, in: Deformation-Mechanism Maps, Pergamon, Oxford, 1982, p. 44. [15] N.J. Petch, J. Iron Steel Inst. 174 (1953) 25. [16] G. Nussbaum, P. Sainfort, G. Regazzoni, H. Gjestland, Scrip. Metall. 23 (1989) 1079. [17] M. Mabuchi, K. Higashi, Phil. Mag. A74 (1996) 887.