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Exceptional mechanical properties of an Mg97Y2Zn1 alloy wire strengthened by dispersive LPSO particle clusters
Accepted Manuscript Exceptional mechanical properties of an Mg97Y2Zn1 alloy wire strengthened by dispersive LPSO particle clusters Kai Yan, Jiapeng Sun, Huan Liu, Honghui Cheng, Jing Bai, Xin Huang PII: DOI: Reference:
S0167-577X(19)30123-5 https://doi.org/10.1016/j.matlet.2019.01.089 MLBLUE 25634
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
21 November 2018 13 January 2019 14 January 2019
Please cite this article as: K. Yan, J. Sun, H. Liu, H. Cheng, J. Bai, X. Huang, Exceptional mechanical properties of an Mg97Y2Zn1 alloy wire strengthened by dispersive LPSO particle clusters, Materials Letters (2019), doi: https:// doi.org/10.1016/j.matlet.2019.01.089
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Exceptional mechanical properties of an Mg97Y2Zn1 alloy wire strengthened by dispersive LPSO particle clusters Kai Yana*, Jiapeng Sunb, Huan Liub*, Honghui Chenga, Jing Baic, Xin Huanga a
College of Mechanical Engineering, Yangzhou University, Yangzhou 225127, China
b
College of Mechanics and Materials, Hohai University, Nanjing 211100, China
c
College of Materials Science and Engineering, Southeast University, Nanjing 211189, China
*Corresponding authors. E-mail address: [email protected] (H. Liu); [email protected] (K. Yan) Abstract A 0.31mm-diameter Mg97Y2Zn1 alloy wire with high yield strength of 550 MPa, ultimate tensile strength of 570 MPa and elongation of 12% was successfully prepared via the combination of ECAP and heavy drawing at elevated temperatures. Microstructure observation showed that the 18R phases were broken into fine particles and formed clusters during drawing of ECAP rod. The α-Mg matrix was refined via dynamic recrystallization, and the DRX grains were mixed with dynamically precipitated 14H particles. The ultra-fined microstructure, as well as the homogenous distribution of LPSO particles and clusters, contributed to the exceptional mechanical properties of Mg97Y2Zn1 alloy wire. Keywords: Metals and alloys; Long period stacking ordered phase; Equal channel angular pressing; Microstructure; Mechanical property. 1. Introduction Mg-RE-Zn alloys containing long period stacking ordered (LPSO) structure exhibit great potential in aerospace, military, automobile and biomedical applications due to their promising high-strength and reasonable ductility at both room temperature and elevated temperatures [1]. By now, the most high strength of magnesium alloy was acquired in 2001 by Kawamura et al. via a rapidly solidified powder metallurgy (RS/PM) method [2]. The RS/PM Mg97Y2Zn1 (at%) alloy possessed high tensile yield strength of 610 MPa and elongation of 5% at room temperature. Its high strength was attributed to the nanocrystalline α-Mg grains (100～200 nm) and uniformly dispersed Mg24Y5 and LPSO particles [3]. Since then, most researchers have tried to prepare high-strength
LPSO-reinforced
alloys
via
conventional 1
casting,
heat
treatment
and
thermomechanical processing. Two strategies, alloying with multiple elements and combined plastic processing, have been widely employed to further enhance the Mg-RE-TM alloys [4]. It has been reported that the extruded and aged Mg-Gd-Y-Zn-Zr alloys could achieve high ultimate tensile strength over 500 MPa, owing to the synergetic strengthening effects of fine grain strengthening, LPSO strengthening, texture strengthening and precipitation strengthening [5]. However, these alloys usually contain high RE contents (> 10 wt.%), which increases the cost and density of the alloys. Recently, Mg alloy wires have been developed, which exhibited much higher strength than hot extruded or SPD-processed alloys [6]. Therefore, in this paper, to excavate the strength potential of low-alloyed Mg97Y2Zn1 alloy, an alloy wire with exceptional mechanical properties was developed via combining ECAP and heavy drawing, and its microstructure was investigated. 2. Experimental The starting material is the as-extruded Mg97Y2Zn1 alloy rod with diameter of 20 mm, as described in reference [7]. Samples with size of ϕ15 mm70 mm were then cut from the extruded rod for ECAP. The ECAP processing was carried out for 6 passes via route Bc using a die with channel diameter of ϕ15 mm and die angle of 90 at 633 K at a constant extrusion speed of 1 mm/s. The un-ECAP and ECAP rods were named as Rod-1 and Rod-2, respectively. Then, a two-stage multi-pass drawing was conducted on Rod-1 and Rod-2 samples at 673 K at a drawing speed of 6 mm/s. The diameter was reduced from 15 mm to 0.96 mm after 20-pass drawing with single-pass deformation of 25～36% in the first step, and from 0.96 mm to 0.31 mm after 11-pass drawing with single-pass deformation of 15～22% in the second step. The wires obtained from Rod-1 and Rod-2 were then named as Wire-1 and Wire-2, respectively. The microstructure observation of the alloys was performed by using a scanning electron microscope (SEM, Hitachi S-4800II) and a transmission electron microscope (TEM, Tecnai G2). Tensile tests of the samples were carried out by an Instron 3367 electronic universal testing machine at a speed of 1 mm/min, with sample gauge length of 100 mm. 3. Results and discussion Fig. 1 shows the typical engineering stress-strain curves and mechanical properties values of the studied alloys. It is apparent that both wires exhibit high tensile yield strengths (TYS) over 400 2
MPa. Especially, the Wire-2 has an exceptional tensile property with ultimate tensile strength (UTS) of 570 MPa and TYS of 550 MPa, together with good ductility of elongation 12%. Such integrated high strength and high ductility are rarely reported in Mg-Y-Zn alloys. Seen from Fig. 1(b), although both the strength and elongation of Rod-2 are higher than that of Rod-1, the difference is unconspicuous. However, a leap occurs after hot drawing of ECAP rod, which must be originated from the microstructure evolutions during heavy drawing. Fig. 2 (a) and (b) show the SEM micrographs of cross sections of Rod-1 and Rod-2 samples. The as-extruded Rod-1 is composed of bright block 18R LPSO phase and dark α-Mg matrix. Some lamellae are also observed within α-Mg grains, which are 14H LPSO phases according to our previous studies [7]. Moreover, the 18R LPSO phase is distorted or kinked, but the 14H LPSO structure is straight, suggesting the 14H lamellae could be formed during cooling of extruded bars. Regarding to the Rod-2, after six passes of ECAP, the α-Mg grains are obviously refined by dynamic recrystallization (DRX) and the LPSO structure is severely deformed, even partially breaking into small particles. As marked in Fig. 2(b), abundant LPSO particles are dispersed and mixed with the α-Mg DRX grains, or aggregated as clusters. As seen in Fig. 2(c), great changes in microstructure have happened after heavy drawing of Rod-1. The original kinked 18R LPSO phase almost disappears, and the dense clusters of intermetallic phases are uniformly distributed within the matrix. Moreover, some unbroken LPSO phase exhibits lath-shape, delaminated and elongated along the drawing direction. However, with the aid of ECAP before drawing, the LPSO phases in Wire-2 are broken into fine particles completely and transformed into the denser clusters, as shown in Fig. 2(d). It is evident that the Wire-2 has a more uniform and finer microstructure than Wire-1, which can be attributed to the pre-refining effect of ECAP before drawing. ECAP mainly produces shearing deformation in the alloy, resulting in the kinking and crushing of LPSO structure with increased ECAP passes [8]. While the drawing and extrusion produce tense and compress deformation, causing the LPSO phase bent and elongated. The above results indicate that it is more effective to promote homogeneous and refined microstructure with the combination of ECAP and drawing. Fig. 3(a) shows the TEM micrograph of Wire-1. It is apparent that a band-like microstructure forms, which consists of alternately arranged dark bands of clusters and bright bands of α-Mg 3
matrix. The dynamic recrystallization occurs in the bright regions, and the grain sizes of DRX grains are about 0.5 ～ 1μm. Similar microstructure is also confirmed in Wire-2, but its microstructure is finer, as seen from Fig. 3(b). Moreover, the average distance between the adjacent cluster bands of Wire-2 is smaller than that of Wire-1. The α-Mg bands in Wire-1 contain three or four columns of α-Mg DRX grains, while it is only one column of α-Mg grains for Wire-2. Fig. 3(c) and (d) show the morphology of clusters. From the corresponding diffraction rings inset of Fig. 3(c), it can be confirmed that the LPSO grains within the clusters possess near nanocrystalline structure. The corresponding selected area electron diffraction (SAED) pattern (inset of Fig. 3(d)) suggests the particle phase is 18R LPSO structure, and no 14H phase is detected within the clusters. Fig. 3(e) shows the TEM morphology of a α-Mg band region. Apart from the fine DRX grains, some isolated particles are distributed along grain boundaries. The enlargement of several particles are illustrated in Fig. 3(f). The lamellar contrasts within the particles reveal the existence of LPSO structure, and its corresponding SAED pattern demonstrates they are 14H LPSO phases. Thus, the microstructure of the high-performance Wire-2 is clearly resolved as a fine band structure with alternately distributed LPSO bands (18R clusters) and DRX bands (mixed DRX and 14H grains). It has been reported that the strengthening mechanism of LPSO phase in wrought Mg-RE-Zn alloys mainly resulted from the short-fiber strengthening of LPSO stripes aligned along deformation directions, as well as the strengthening of LPSO kinking bands [9-11]. These conclusions were derived from the as-extruded Mg-Y-Zn alloys where 18R LPSO phase is kinked but not refined. In this paper, kinking of 18R phases is rarely observed in Wire-2. Instead, a microstructure with dispersive 18R particles or clusters was first prepared during combined ECAP and drawing. Therefore, short-fiber strengthening and kinking bands strengthening cannot be operative for this high-strength wire. Interestingly, this Mg97Y2Zn1 wire shows much higher strength than conventionally extruded Mg-Y-Zn alloys, suggesting the finely dispersed LPSO particles (clusters) are more effective in enhancing magnesium alloys. We consider that the fine and dispersed 18R particles (cluster) are responsible for the high strength, which might operate via a volume based strengthening. The detailed strengthening mechanism of this unique 4
microstructure need to be further investigated. 4. Conclusions This paper reports a 0.31 mm-diameter Mg97Y2Zn1 alloy wire with exceptional high UTS of 570 MPa and elongation of 12% prepared by combined ECAP and heavy drawing. Due to the pre-refining effect of ECAP prior to drawing, the alloy wire exhibits a homogeneous and refined band microstructure. The 18R phase is broken into dispersive particles and clusters. The α-Mg bands are composed of mixed DRX grains and 14H particles. This novel microstructure contributes to the synchronously improved strength and ductility.
Conflict of Interest The authors declare that they have no conflict of interest.
Acknowledgement The work is supported by the National Natural Science Foundation of China (No. 51301151) and Jiangsu Province Natural Science Foundation of China (No. BK20130447 and BK20160869). References [1] X.J. Wang, D.K. Xu, R.Z. Wu, X.B. Chen, Q.M. Peng, L. Jin, Y.C. Xin, Z.Q. Zhang, Y. Liu, X.H. Chen, G. Chen, K.K. Deng, H.Y. Wang, J. Mater. Sci. Technol. 34 (2018) 245-247. [2] Y. Kawamura, K. Hayashi, A. Inoue, T. Masumoto, Mater. Trans. 42 (2001) 1172-1176. [3] E. Abe, Y. Kawamura, K. Hayashi, A. Inoue, Acta Mater. 50 (2002) 3845-3857. [4] D.K. Xu, E.H. Han, Y.B. Xu, Prog. Nat. Sci. Mater. 26 (2016) 117-128. [5] C. Xu, G.H. Fan, T. Nakata, X. Liang, Y.Q. Chi, X.G. Qiao, G.J. Cao, T.T. Zhang, M. Huang, K.S. Miao, M.Y. Zheng, S. Kamado, H.L. Xie, Metall. Mater. Trans. A 49 (2018) 1931–1947. [6] K. Yan, J.P. Sun, J. Bai, H. Liu, X. Huang, Z.Y. Jin, Y.N. Wu, Mater. Sci. Eng. A 739 (2019) 513-518. [7] H. Liu, J. Bai, K. Yan, J.L. Yan, A.B. Ma, J.H. Jiang, Mater. Des. 93 (2016) 9-18. [8] H. Liu, J. Ju, X.W. Yang, J.L. Yan, D. Song, J.H. Jiang, A.B. Ma, J Alloy. Compd. 704 (2017) 509-517. 5
[9] K. Hagihara, A. Kinoshita, Y. Sugino, M. Yamasaki, Y. Kawamura, H. Y. Yasuda, Y. Umakoshi, Acta Mater. 58 (2010) 6282-6293. [10] K. Hagihara, Z.X. Li, M. Yamasaki, Y. Kawamura, T. Nakano, Mater. Lett. 214 (2018) 119-122 [11] K. Hagihara, Z.X. Li, M. Yamasaki, Y. Kawamura, T. Nakano, Acta Mater. 163 (2019) 226-239
6
(a)
(b)
Fig.1. (a) The tensile engineering stress and strain curves of Wire-1 and Wire-2 samples, and (b) the UTS, TYS and Elongation values for Rod-1, Rod-2, Wire-1 and Wire-2 samples.
(a)
(b) Aggregated 18R particles
Undeformed 14H
DRXed α-Mg Kinked 18R α-Mg
Dispersed 18R particles Kinked 18R
10 μm
(c)
10 μm
(d) Delaminated LPSO Elongated LPSO
10 μm
10 μm
Fig.2. SEM images of (a) Rod-1, (b) Rod-2, (c) Wire-1 and (d) Wire-2 samples.
7
(a)
(b) LPSO clusters
LPSO clusters
DRX grains
1 μm
1 μm
(c)
(d)
18R LPSO structure
Particle clusters region
00018 0001
200 nm
(e)
50 nm
(f)
DRX grains 14H LPSO structure 00014
LPSO Particles
0001 50 nm
500 nm
Fig. 3. TEM micrographs of the Wire-1 and Wire-2 samples: The band-like structures in (a) Wire-1 and (b) Wire-1. (c) The cluster and its corresponding SAED pattern. (d) The 18R LPSO 8
structure within clusters and its corresponding SAED pattern. (e) The α-Mg grain regions. (f) The 14H LPSO phase particles in α-Mg grain regions and its corresponding SAED pattern.
9
A Mg97Y2Zn1 wire was prepared via combined ECAP and drawing. The wire exhibited ultimate tensile strength of 570 MPa and elongation of 12%. Refined and dispersive 18R LPSO clusters contributed to the improved mechanical properties.
10
S0167-577X(19)30123-5 https://doi.org/10.1016/j.matlet.2019.01.089 MLBLUE 25634
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
21 November 2018 13 January 2019 14 January 2019
Please cite this article as: K. Yan, J. Sun, H. Liu, H. Cheng, J. Bai, X. Huang, Exceptional mechanical properties of an Mg97Y2Zn1 alloy wire strengthened by dispersive LPSO particle clusters, Materials Letters (2019), doi: https:// doi.org/10.1016/j.matlet.2019.01.089
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Exceptional mechanical properties of an Mg97Y2Zn1 alloy wire strengthened by dispersive LPSO particle clusters Kai Yana*, Jiapeng Sunb, Huan Liub*, Honghui Chenga, Jing Baic, Xin Huanga a
College of Mechanical Engineering, Yangzhou University, Yangzhou 225127, China
b
College of Mechanics and Materials, Hohai University, Nanjing 211100, China
c
College of Materials Science and Engineering, Southeast University, Nanjing 211189, China
*Corresponding authors. E-mail address: [email protected] (H. Liu); [email protected] (K. Yan) Abstract A 0.31mm-diameter Mg97Y2Zn1 alloy wire with high yield strength of 550 MPa, ultimate tensile strength of 570 MPa and elongation of 12% was successfully prepared via the combination of ECAP and heavy drawing at elevated temperatures. Microstructure observation showed that the 18R phases were broken into fine particles and formed clusters during drawing of ECAP rod. The α-Mg matrix was refined via dynamic recrystallization, and the DRX grains were mixed with dynamically precipitated 14H particles. The ultra-fined microstructure, as well as the homogenous distribution of LPSO particles and clusters, contributed to the exceptional mechanical properties of Mg97Y2Zn1 alloy wire. Keywords: Metals and alloys; Long period stacking ordered phase; Equal channel angular pressing; Microstructure; Mechanical property. 1. Introduction Mg-RE-Zn alloys containing long period stacking ordered (LPSO) structure exhibit great potential in aerospace, military, automobile and biomedical applications due to their promising high-strength and reasonable ductility at both room temperature and elevated temperatures [1]. By now, the most high strength of magnesium alloy was acquired in 2001 by Kawamura et al. via a rapidly solidified powder metallurgy (RS/PM) method [2]. The RS/PM Mg97Y2Zn1 (at%) alloy possessed high tensile yield strength of 610 MPa and elongation of 5% at room temperature. Its high strength was attributed to the nanocrystalline α-Mg grains (100～200 nm) and uniformly dispersed Mg24Y5 and LPSO particles [3]. Since then, most researchers have tried to prepare high-strength
LPSO-reinforced
alloys
via
conventional 1
casting,
heat
treatment
and
thermomechanical processing. Two strategies, alloying with multiple elements and combined plastic processing, have been widely employed to further enhance the Mg-RE-TM alloys [4]. It has been reported that the extruded and aged Mg-Gd-Y-Zn-Zr alloys could achieve high ultimate tensile strength over 500 MPa, owing to the synergetic strengthening effects of fine grain strengthening, LPSO strengthening, texture strengthening and precipitation strengthening [5]. However, these alloys usually contain high RE contents (> 10 wt.%), which increases the cost and density of the alloys. Recently, Mg alloy wires have been developed, which exhibited much higher strength than hot extruded or SPD-processed alloys [6]. Therefore, in this paper, to excavate the strength potential of low-alloyed Mg97Y2Zn1 alloy, an alloy wire with exceptional mechanical properties was developed via combining ECAP and heavy drawing, and its microstructure was investigated. 2. Experimental The starting material is the as-extruded Mg97Y2Zn1 alloy rod with diameter of 20 mm, as described in reference [7]. Samples with size of ϕ15 mm70 mm were then cut from the extruded rod for ECAP. The ECAP processing was carried out for 6 passes via route Bc using a die with channel diameter of ϕ15 mm and die angle of 90 at 633 K at a constant extrusion speed of 1 mm/s. The un-ECAP and ECAP rods were named as Rod-1 and Rod-2, respectively. Then, a two-stage multi-pass drawing was conducted on Rod-1 and Rod-2 samples at 673 K at a drawing speed of 6 mm/s. The diameter was reduced from 15 mm to 0.96 mm after 20-pass drawing with single-pass deformation of 25～36% in the first step, and from 0.96 mm to 0.31 mm after 11-pass drawing with single-pass deformation of 15～22% in the second step. The wires obtained from Rod-1 and Rod-2 were then named as Wire-1 and Wire-2, respectively. The microstructure observation of the alloys was performed by using a scanning electron microscope (SEM, Hitachi S-4800II) and a transmission electron microscope (TEM, Tecnai G2). Tensile tests of the samples were carried out by an Instron 3367 electronic universal testing machine at a speed of 1 mm/min, with sample gauge length of 100 mm. 3. Results and discussion Fig. 1 shows the typical engineering stress-strain curves and mechanical properties values of the studied alloys. It is apparent that both wires exhibit high tensile yield strengths (TYS) over 400 2
MPa. Especially, the Wire-2 has an exceptional tensile property with ultimate tensile strength (UTS) of 570 MPa and TYS of 550 MPa, together with good ductility of elongation 12%. Such integrated high strength and high ductility are rarely reported in Mg-Y-Zn alloys. Seen from Fig. 1(b), although both the strength and elongation of Rod-2 are higher than that of Rod-1, the difference is unconspicuous. However, a leap occurs after hot drawing of ECAP rod, which must be originated from the microstructure evolutions during heavy drawing. Fig. 2 (a) and (b) show the SEM micrographs of cross sections of Rod-1 and Rod-2 samples. The as-extruded Rod-1 is composed of bright block 18R LPSO phase and dark α-Mg matrix. Some lamellae are also observed within α-Mg grains, which are 14H LPSO phases according to our previous studies [7]. Moreover, the 18R LPSO phase is distorted or kinked, but the 14H LPSO structure is straight, suggesting the 14H lamellae could be formed during cooling of extruded bars. Regarding to the Rod-2, after six passes of ECAP, the α-Mg grains are obviously refined by dynamic recrystallization (DRX) and the LPSO structure is severely deformed, even partially breaking into small particles. As marked in Fig. 2(b), abundant LPSO particles are dispersed and mixed with the α-Mg DRX grains, or aggregated as clusters. As seen in Fig. 2(c), great changes in microstructure have happened after heavy drawing of Rod-1. The original kinked 18R LPSO phase almost disappears, and the dense clusters of intermetallic phases are uniformly distributed within the matrix. Moreover, some unbroken LPSO phase exhibits lath-shape, delaminated and elongated along the drawing direction. However, with the aid of ECAP before drawing, the LPSO phases in Wire-2 are broken into fine particles completely and transformed into the denser clusters, as shown in Fig. 2(d). It is evident that the Wire-2 has a more uniform and finer microstructure than Wire-1, which can be attributed to the pre-refining effect of ECAP before drawing. ECAP mainly produces shearing deformation in the alloy, resulting in the kinking and crushing of LPSO structure with increased ECAP passes [8]. While the drawing and extrusion produce tense and compress deformation, causing the LPSO phase bent and elongated. The above results indicate that it is more effective to promote homogeneous and refined microstructure with the combination of ECAP and drawing. Fig. 3(a) shows the TEM micrograph of Wire-1. It is apparent that a band-like microstructure forms, which consists of alternately arranged dark bands of clusters and bright bands of α-Mg 3
matrix. The dynamic recrystallization occurs in the bright regions, and the grain sizes of DRX grains are about 0.5 ～ 1μm. Similar microstructure is also confirmed in Wire-2, but its microstructure is finer, as seen from Fig. 3(b). Moreover, the average distance between the adjacent cluster bands of Wire-2 is smaller than that of Wire-1. The α-Mg bands in Wire-1 contain three or four columns of α-Mg DRX grains, while it is only one column of α-Mg grains for Wire-2. Fig. 3(c) and (d) show the morphology of clusters. From the corresponding diffraction rings inset of Fig. 3(c), it can be confirmed that the LPSO grains within the clusters possess near nanocrystalline structure. The corresponding selected area electron diffraction (SAED) pattern (inset of Fig. 3(d)) suggests the particle phase is 18R LPSO structure, and no 14H phase is detected within the clusters. Fig. 3(e) shows the TEM morphology of a α-Mg band region. Apart from the fine DRX grains, some isolated particles are distributed along grain boundaries. The enlargement of several particles are illustrated in Fig. 3(f). The lamellar contrasts within the particles reveal the existence of LPSO structure, and its corresponding SAED pattern demonstrates they are 14H LPSO phases. Thus, the microstructure of the high-performance Wire-2 is clearly resolved as a fine band structure with alternately distributed LPSO bands (18R clusters) and DRX bands (mixed DRX and 14H grains). It has been reported that the strengthening mechanism of LPSO phase in wrought Mg-RE-Zn alloys mainly resulted from the short-fiber strengthening of LPSO stripes aligned along deformation directions, as well as the strengthening of LPSO kinking bands [9-11]. These conclusions were derived from the as-extruded Mg-Y-Zn alloys where 18R LPSO phase is kinked but not refined. In this paper, kinking of 18R phases is rarely observed in Wire-2. Instead, a microstructure with dispersive 18R particles or clusters was first prepared during combined ECAP and drawing. Therefore, short-fiber strengthening and kinking bands strengthening cannot be operative for this high-strength wire. Interestingly, this Mg97Y2Zn1 wire shows much higher strength than conventionally extruded Mg-Y-Zn alloys, suggesting the finely dispersed LPSO particles (clusters) are more effective in enhancing magnesium alloys. We consider that the fine and dispersed 18R particles (cluster) are responsible for the high strength, which might operate via a volume based strengthening. The detailed strengthening mechanism of this unique 4
microstructure need to be further investigated. 4. Conclusions This paper reports a 0.31 mm-diameter Mg97Y2Zn1 alloy wire with exceptional high UTS of 570 MPa and elongation of 12% prepared by combined ECAP and heavy drawing. Due to the pre-refining effect of ECAP prior to drawing, the alloy wire exhibits a homogeneous and refined band microstructure. The 18R phase is broken into dispersive particles and clusters. The α-Mg bands are composed of mixed DRX grains and 14H particles. This novel microstructure contributes to the synchronously improved strength and ductility.
Conflict of Interest The authors declare that they have no conflict of interest.
Acknowledgement The work is supported by the National Natural Science Foundation of China (No. 51301151) and Jiangsu Province Natural Science Foundation of China (No. BK20130447 and BK20160869). References [1] X.J. Wang, D.K. Xu, R.Z. Wu, X.B. Chen, Q.M. Peng, L. Jin, Y.C. Xin, Z.Q. Zhang, Y. Liu, X.H. Chen, G. Chen, K.K. Deng, H.Y. Wang, J. Mater. Sci. Technol. 34 (2018) 245-247. [2] Y. Kawamura, K. Hayashi, A. Inoue, T. Masumoto, Mater. Trans. 42 (2001) 1172-1176. [3] E. Abe, Y. Kawamura, K. Hayashi, A. Inoue, Acta Mater. 50 (2002) 3845-3857. [4] D.K. Xu, E.H. Han, Y.B. Xu, Prog. Nat. Sci. Mater. 26 (2016) 117-128. [5] C. Xu, G.H. Fan, T. Nakata, X. Liang, Y.Q. Chi, X.G. Qiao, G.J. Cao, T.T. Zhang, M. Huang, K.S. Miao, M.Y. Zheng, S. Kamado, H.L. Xie, Metall. Mater. Trans. A 49 (2018) 1931–1947. [6] K. Yan, J.P. Sun, J. Bai, H. Liu, X. Huang, Z.Y. Jin, Y.N. Wu, Mater. Sci. Eng. A 739 (2019) 513-518. [7] H. Liu, J. Bai, K. Yan, J.L. Yan, A.B. Ma, J.H. Jiang, Mater. Des. 93 (2016) 9-18. [8] H. Liu, J. Ju, X.W. Yang, J.L. Yan, D. Song, J.H. Jiang, A.B. Ma, J Alloy. Compd. 704 (2017) 509-517. 5
[9] K. Hagihara, A. Kinoshita, Y. Sugino, M. Yamasaki, Y. Kawamura, H. Y. Yasuda, Y. Umakoshi, Acta Mater. 58 (2010) 6282-6293. [10] K. Hagihara, Z.X. Li, M. Yamasaki, Y. Kawamura, T. Nakano, Mater. Lett. 214 (2018) 119-122 [11] K. Hagihara, Z.X. Li, M. Yamasaki, Y. Kawamura, T. Nakano, Acta Mater. 163 (2019) 226-239
6
(a)
(b)
Fig.1. (a) The tensile engineering stress and strain curves of Wire-1 and Wire-2 samples, and (b) the UTS, TYS and Elongation values for Rod-1, Rod-2, Wire-1 and Wire-2 samples.
(a)
(b) Aggregated 18R particles
Undeformed 14H
DRXed α-Mg Kinked 18R α-Mg
Dispersed 18R particles Kinked 18R
10 μm
(c)
10 μm
(d) Delaminated LPSO Elongated LPSO
10 μm
10 μm
Fig.2. SEM images of (a) Rod-1, (b) Rod-2, (c) Wire-1 and (d) Wire-2 samples.
7
(a)
(b) LPSO clusters
LPSO clusters
DRX grains
1 μm
1 μm
(c)
(d)
18R LPSO structure
Particle clusters region
00018 0001
200 nm
(e)
50 nm
(f)
DRX grains 14H LPSO structure 00014
LPSO Particles
0001 50 nm
500 nm
Fig. 3. TEM micrographs of the Wire-1 and Wire-2 samples: The band-like structures in (a) Wire-1 and (b) Wire-1. (c) The cluster and its corresponding SAED pattern. (d) The 18R LPSO 8
structure within clusters and its corresponding SAED pattern. (e) The α-Mg grain regions. (f) The 14H LPSO phase particles in α-Mg grain regions and its corresponding SAED pattern.
9
A Mg97Y2Zn1 wire was prepared via combined ECAP and drawing. The wire exhibited ultimate tensile strength of 570 MPa and elongation of 12%. Refined and dispersive 18R LPSO clusters contributed to the improved mechanical properties.
10