- Email: [email protected]
Joining of Zr51Ti5Ni10Cu25Al9 BMG to aluminum alloy by friction stir welding
Accepted Manuscript Joining of Zr51Ti5Ni10Cu25Al9 BMG to aluminum alloy by friction stir welding Hao Zhang, Yunzhuo Lu, Yongjiang Huang, Aihan Feng, Zuoxiang Qin, Xing Lu PII:
S0042-207X(15)00282-1
DOI:
10.1016/j.vacuum.2015.06.020
Reference:
VAC 6724
To appear in:
Vacuum
Received Date: 11 April 2015 Revised Date:
9 June 2015
Accepted Date: 10 June 2015
Please cite this article as: Zhang H, Lu Y, Huang Y, Feng A, Qin Z, Lu X, Joining of Zr51Ti5Ni10Cu25Al9 BMG to aluminum alloy by friction stir welding, Vaccum (2015), doi: 10.1016/ j.vacuum.2015.06.020. 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.
ACCEPTED MANUSCRIPT
Joining of Zr51Ti5Ni10Cu25Al9 BMG to aluminum alloy by friction stir welding Hao Zhang a, Yunzhuo Lu a,*, Yongjiang Huang b, Aihan Feng c, Zuoxiang Qin a, Xing Lu a a
SC
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School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028, People’s Republic of China b School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China c School of Materials Science and Engineering, Tongji University, Shanghai 200092, People’s Republic of China * Corresponding author: Tel.: +86-411-84105700; Fax: +86-411-84109417.
M AN U
E-mail address: [email protected] (Yunzhuo Lu)
Abstract
Plates of Zr51Ti5Ni10Cu25Al9 bulk metallic glass (BMG) and 7075 aluminum alloy
TE D
were successfully joined by friction stir welding (FSW). On the aluminum alloy side near the interface, some BMG fragments with irregular shapes and different sizes are
EP
found distributed in the nugget zone. The hardness of 7075 aluminum alloy first decreases and then increases as the distance away from the weld interface. The
AC C
harness of BMG firstly increases as the position moves away from the weld interface. Then the hardness decreases and keeps constant at about 540 Hv. The evolution of the hardness in the BMG side is closely related to the variation of free volume in the glassy alloy.
Keywords: Friction stir welding; bulk metallic glass; aluminum alloy
-1-
ACCEPTED MANUSCRIPT Bulk metallic glasses (BMGs), which are newcomers to the field of amorphous materials, exhibit many unique properties such as high strength, good hardness, and good corrosion resistance [1-4]. However, the small dimension of BMGs in the region
RI PT
of only tens of millimeters severely limits the scope of industrial applications. The employment of welding technique in BMGs is the most likely way to bring about the break through of size restriction. Friction stir welding (FSW) is a new solid-state
SC
joining process used in BMGs [5], in which the heat input is relatively low and an
M AN U
excellent joining can be obtained without any crystallization in the BMGs. For instance, Wang et al. first successfully applied the FSW method to the joining of Zr55Cu30Al10Ni5 BMG with AlZnMgCu alloys, which showed excellent metallurgical bonding and mixed microstructure in the stir zone [6]. Then Ji et al. welded two
TE D
Zr-base BMGs together without crystallization in the stir zone by using the FSW method [7]. Soon after, Qin et al. joined the Zr55Cu30Al10Ni5 BMG with the crystalline Al using the FSW technique [8]. More recently, Sun et al. successfully
EP
welded the Zr55Cu30Al10Ni5 BMG with pure copper by FSW [9].
AC C
In this study, the dissimilar FSW of Zr51Ti5Ni10Cu25Al9 BMG to the widely used 7075 aluminum alloy has been tried. The microstructure evolution and the hardness of the welded joint were investigated and discussed after the welding. Zr51Ti5Ni10Cu25Al9 alloy ingots were produced by arc-melting a mixture of the
starting commercial-grade pure elements, each with 99.0 wt. % purity or better, under a Ti-gettered argon atmosphere. To achieve the chemical homogeneity, each ingot was remelted at least four times. Metallic glass plates with a thickness of 3 mm were
-2-
ACCEPTED MANUSCRIPT produced by drop casting the molten alloys into a copper mold. The amorphous nature of the as-cast samples was confirmed by using x-ray diffraction (XRD) with Cu Kα radiation. Then rectangular plates with the thickness of 1.6 mm were cut from as-cast
RI PT
metallic glasses by wire-electrode cutting. The surfaces of the obtained samples were polished with refined abrasive paper carefully for FSW experiments. Plates of 7075 aluminum alloy with a composition of Al-5.6Zn-2.5Mg-1.6Cu-0.23Cr (wt.%) were
SC
friction stir welded with the Zr51Ti5Ni10Cu25Al9 BMG at a welding speed of 100
M AN U
mm/min and a tool rotation speed of 800 rpm. The tool used had a shoulder 12 mm in diameter and a cylindrical pin 4 mm in diameter and 1.5 mm in length. During the FSW process, the BMG was put on the advance side and the 7075 alloy on the retreating side. The tool probe was offset into the 7075 alloy side with the lateral
TE D
surface of the probe slightly touching the BMG side. The welded samples were observed using scanning electron microscopy (SEM) on a polished cross-section etched by a solution of 30% HNO3 and 70% CH3OH. The distribution of chemical
EP
elements near the interface was determined by energy dispersive X-ray spectroscopy.
AC C
The phases were identified by micro-area X-ray diffractometry using Cu Kα radiation. The Vickers hardness profile of the weld was measured on the cross-section along the center line of the welded plate. The cross-sectional micrograph shown in Fig. 1 exhibits the microstructure of the
FSW BMG/aluminum alloy joint. As shown in Fig. 1(a), two different materials can be easily distinguished, namely the Zr51Ti5Ni10Cu25Al9 BMG on the lower side and the 7075 aluminum alloy on the upper side of the interface. However, some BMG
-3-
ACCEPTED MANUSCRIPT fragments with different sizes and irregular shapes are found distributed in the aluminum alloy side near the interface, indicating that parts of the BMG are shattered into tiny particles and stirred into the aluminum matrix during FSW process. Figure
RI PT
1(b) shows a typical magnified interface of FSW BMG/aluminum alloy joint. No weld defects can be detected along the weld interface, indicating that a sound welding was obtained between the BMG and aluminum alloy by FSW. However, some
SC
micro-voids can be observed around the large BMG fragments, which are shown in
the blocky BMG fragments [9].
M AN U
Fig. 1(c). The formation of the micro-voids might be related to the irregular shape of
Figure 2 shows the XRD patterns measured at the Zr51Ti5Ni10Cu25Al9 BMG, the 7075 aluminum alloy and the interface in the stir zone. As shown in curve (a), there is
TE D
a broaden peak in 2 theta region of 30~45° without any detectable crystalline Bragg peaks, indicating the amorphous structure of Zr51Ti5Ni10Cu25Al9 BMG. In contrast, the 7075 aluminum alloy is characterized by crystalline Bragg peaks shown in curve
EP
(c). For the BMG-7075 alloy interface, the XRD curve (b) exhibits a superimposition
AC C
of sharp peaks corresponding to the crystalline phase on the broad halo peak coming from the amorphous phase, indicating the existence of a mixture of the amorphous and some crystalline phases. The position and the intensity of the sharp crystalline peaks match exactly with that of Al. No other phases can be detected within the sensitivity limit of XRD, indicating that no chemical reaction took place between the two materials during the entire FSW process. Figure 3 shows the hardness profile of the BMG/aluminum alloy interface. The
-4-
ACCEPTED MANUSCRIPT zero point denotes the interface between the two materials. The left side exhibits the hardness of 7075 aluminum alloy. It can be seen that the hardness of 7075 aluminum alloy first decreases and then increases as the distance away from the weld interface.
RI PT
It has reported that the hardness of the aluminum alloy is mainly governed by the precipitates [10]. The precipitates in the nugget zone (NZ) and the heat affected zone (HAZ) will coarsen and/or dissolve, resulting in the reduced hardness [6]. The
SC
following increase of the hardness indicates that the hardness gradually approaches to
M AN U
the hardness of the base aluminum alloy. The right side illustrates the hardness of the Zr51Ti5Ni10Cu25Al9 BMG. Clearly, three different regions can be. The harness of BMG firstly increases as the position moves away from the weld interface. Then the hardness decreases and finally keeps constant at about 540 Hv. The evolution of the
TE D
hardness is closely related to the variation of free volume in the glassy alloy. Van den Beukel et al. [11] assumed that the change in the enthalpy upon structural relaxation is due to the variation of the free volume. Thus, it is reasonable to estimate the relative
EP
change in the free volume by the variation of the relaxation enthalpy (Hr) [12,13].
AC C
Figure 4 presents the thermograms of Zr51Ti5Ni10Cu25Al9 specimens with different distances away from the weld interface. The corresponding results of Hr versus the distances away from the weld interface are shown in the inset figure of Fig. 4. It is found that Hr first decreases and then increase with the distance moves away from the weld interface. According to the previous reports [14, 15], upon sub-Tg reheating, the excess free volume can be annihilated out of the metallic glass. When the sample is reheated to the temperature above Tg, the relaxed free volume in the bulk metallic
-5-
ACCEPTED MANUSCRIPT glasses can be restored. It has reported that the temperatures adjacent to NZ during the FSW procedure should be higher than Tg and lower than the crystallization temperature (Tx) [6]. Therefore, the relatively high Hr adjacent to the NZ can be
RI PT
ascribed to the recreation of the relaxed free volume induced by heating the sample above Tg. The first decrease of the Hr, indicating the reduction of the recreated free volume, is closely related to the decrease of temperature. Then it is reasonable to
SC
speculate that the reduction of the recreated free volume is the main reason for the
M AN U
first increase in the hardness of BMG. The following increase of the Hr, attributing to the increase of the free volume, induces the decrease of the hardness of BMG. When the temperature is lower than a certain value Tc, the heat may have a little influence on the free volume. Therefore, the hardnesses of BMG keep constant at about 540 Hv,
TE D
which coincides with the hardness of the as-cast Zr51Ti5Ni10Cu25Al9 BMG [16]. In summary, Zr51Ti5Ni10Cu25Al9 BMG were successfully friction stir welded to 7075 aluminum alloy. On the aluminum alloy side near the interface, some BMG
EP
fragments with irregular shapes and different sizes are found distributed in the nugget
AC C
zone. The hardness of 7075 aluminum alloy first decreases and then increases as the distance away from the weld interface. The harness of BMG firstly increases as the position moves away from the weld interface. Then the hardness decreases and keeps constant at about 540 Hv. The evolution of the hardness in the BMG side is closely related to the variation of free volume in the glassy alloy.
Acknowledgments This work was supported by the National Natural Science Foundation of China
-6-
ACCEPTED MANUSCRIPT (NSFC) under Grant Nos. 51401041 and 51025415.
References [1] Hu Z, Zhao ZQ, Wu YD, Lu T, Xing JS, Wei BC. Vacuum 2013;89:142-6.
2014;101:98-101. [3] Hua NB, Zhang T. J Alloys Compd 2014;602:339-45.
RI PT
[2] Tariq NH, Shakil M, Hasan BA, Akhter JI, Haq MA, Awan NA. Vacuum
M AN U
ZhaoYT, Wang J. Mater Lett 2007;61:2170-2.
SC
[4] Wang XY, Wang WK, Zhan ZJ, Xu FY, Zhang NY, Wang FX, ChenY, Pang LP,
[5] Liu X, Lan SH, Ni J. Mater Des 2014;59:50-62.
[6] Wang D, Xiao BL, Ma ZY, Zhang H.F. Scripta Mater 2009;60:112-5. [7] Ji YS, Fujii H, Sun Y.F, Maeda M, Nakata K, Kimura H, Inoue A, Nogi K. Mater
TE D
Trans 2009;50:1300-3.
[8] Qin ZX, Li CH, Zhang HF, Wang ZG, Hu ZQ, Liu Z.Q. J Mater Sci Technol 2009;25:853-6.
EP
[9] Sun Y, Ji Y, Fujii H, Nakata K, Nogi K. Mater Sci Eng A 2010;527:3427-32.
AC C
[10] Xie GM, Ma ZY, Geng L. J Mater Sci Technol 2009;25:351-5. [11] Van den Beukel A, Sietsma J. Acta Metall 1990;38:383-9. [12] Liu JW, Cao QP, Chen LY, Wang XD, Jiang JZ. Acta Mater 2010;58:4827-40. [13] Huang YJ, Sun Y, Shen J. Intermetallics 2010;18:2044-50. [14] Nagel C, Rätzke K, Schmidtke E,
Faupel F, Ulfert W. Phys Rev B
1999;60 :9212. [15] Nagel C, Rätzke K, Schmidtke E, Wolff J, Geyer U, Faupel F. Phys Rev B
-7-
ACCEPTED MANUSCRIPT 1998;57:10224. [16] Cao HB, Ma D, Hsieh KC, Ding L, Stratton WG, Voyles PM, Pan Y, Cai M,
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Dickinson JT, Chang YA. Acta Mater 2006;54:2975-82.
Figure captions
Fig. 1. SEM micrograph of the cross-section in the Zr51Ti5Ni10Cu25Al9 BMG/7075
SC
aluminum alloy.
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Fig. 2. X-ray diffraction patterns of (a) Zr51Ti5Ni10Cu25Al9 BMG, (b) cross-section of joint, (c) 7075 alloy.
Fig. 3. Hardness profile of the BMG/aluminum alloy interface. Fig. 4. Thermograms of Zr51Ti5Ni10Cu25Al9 specimens with different distances away
TE D
from the weld interface. The inset figure is the relaxation enthalpy Er versus the
AC C
EP
distances away from the weld interface.
-8-
ACCEPTED MANUSCRIPT
Fig. 1. SEM micrograph of the cross-section in the Zr51Ti5Ni10Cu25Al9
AC C
EP
TE D
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SC
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BMG/7075 aluminum alloy.
ACCEPTED MANUSCRIPT
Fig. 2. X-ray diffraction patterns of (a) Zr51Ti5Ni10Cu25Al9 BMG, (b) cross-
AC C
EP
TE D
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SC
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section of joint, (c) 7075 alloy.
ACCEPTED MANUSCRIPT
AC C
EP
TE D
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Fig. 3. Hardness profile of the BMG/aluminum alloy interface.
ACCEPTED MANUSCRIPT
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Fig. 4. Thermograms of Zr51Ti5Ni10Cu25Al9 specimens with different distances away from the weld interface. The inset figure is the relaxation
AC C
EP
TE D
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SC
enthalpy Er versus the distances away from the weld interface.
ACCEPTED MANUSCRIPT 1. Zr51Ti5Ni10Cu25Al9 bulk metallic glass and 7075 aluminum alloy were successfully joined by friction stir welding. 2. The hardness of 7075 aluminum alloy first decreases and then increases as the
RI PT
distance away from the weld interface. 3. The evolution of the hardness in the BMG side is related to the variation of free
AC C
EP
TE D
M AN U
SC
volume.
S0042-207X(15)00282-1
DOI:
10.1016/j.vacuum.2015.06.020
Reference:
VAC 6724
To appear in:
Vacuum
Received Date: 11 April 2015 Revised Date:
9 June 2015
Accepted Date: 10 June 2015
Please cite this article as: Zhang H, Lu Y, Huang Y, Feng A, Qin Z, Lu X, Joining of Zr51Ti5Ni10Cu25Al9 BMG to aluminum alloy by friction stir welding, Vaccum (2015), doi: 10.1016/ j.vacuum.2015.06.020. 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.
ACCEPTED MANUSCRIPT
Joining of Zr51Ti5Ni10Cu25Al9 BMG to aluminum alloy by friction stir welding Hao Zhang a, Yunzhuo Lu a,*, Yongjiang Huang b, Aihan Feng c, Zuoxiang Qin a, Xing Lu a a
SC
RI PT
School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028, People’s Republic of China b School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China c School of Materials Science and Engineering, Tongji University, Shanghai 200092, People’s Republic of China * Corresponding author: Tel.: +86-411-84105700; Fax: +86-411-84109417.
M AN U
E-mail address: [email protected] (Yunzhuo Lu)
Abstract
Plates of Zr51Ti5Ni10Cu25Al9 bulk metallic glass (BMG) and 7075 aluminum alloy
TE D
were successfully joined by friction stir welding (FSW). On the aluminum alloy side near the interface, some BMG fragments with irregular shapes and different sizes are
EP
found distributed in the nugget zone. The hardness of 7075 aluminum alloy first decreases and then increases as the distance away from the weld interface. The
AC C
harness of BMG firstly increases as the position moves away from the weld interface. Then the hardness decreases and keeps constant at about 540 Hv. The evolution of the hardness in the BMG side is closely related to the variation of free volume in the glassy alloy.
Keywords: Friction stir welding; bulk metallic glass; aluminum alloy
-1-
ACCEPTED MANUSCRIPT Bulk metallic glasses (BMGs), which are newcomers to the field of amorphous materials, exhibit many unique properties such as high strength, good hardness, and good corrosion resistance [1-4]. However, the small dimension of BMGs in the region
RI PT
of only tens of millimeters severely limits the scope of industrial applications. The employment of welding technique in BMGs is the most likely way to bring about the break through of size restriction. Friction stir welding (FSW) is a new solid-state
SC
joining process used in BMGs [5], in which the heat input is relatively low and an
M AN U
excellent joining can be obtained without any crystallization in the BMGs. For instance, Wang et al. first successfully applied the FSW method to the joining of Zr55Cu30Al10Ni5 BMG with AlZnMgCu alloys, which showed excellent metallurgical bonding and mixed microstructure in the stir zone [6]. Then Ji et al. welded two
TE D
Zr-base BMGs together without crystallization in the stir zone by using the FSW method [7]. Soon after, Qin et al. joined the Zr55Cu30Al10Ni5 BMG with the crystalline Al using the FSW technique [8]. More recently, Sun et al. successfully
EP
welded the Zr55Cu30Al10Ni5 BMG with pure copper by FSW [9].
AC C
In this study, the dissimilar FSW of Zr51Ti5Ni10Cu25Al9 BMG to the widely used 7075 aluminum alloy has been tried. The microstructure evolution and the hardness of the welded joint were investigated and discussed after the welding. Zr51Ti5Ni10Cu25Al9 alloy ingots were produced by arc-melting a mixture of the
starting commercial-grade pure elements, each with 99.0 wt. % purity or better, under a Ti-gettered argon atmosphere. To achieve the chemical homogeneity, each ingot was remelted at least four times. Metallic glass plates with a thickness of 3 mm were
-2-
ACCEPTED MANUSCRIPT produced by drop casting the molten alloys into a copper mold. The amorphous nature of the as-cast samples was confirmed by using x-ray diffraction (XRD) with Cu Kα radiation. Then rectangular plates with the thickness of 1.6 mm were cut from as-cast
RI PT
metallic glasses by wire-electrode cutting. The surfaces of the obtained samples were polished with refined abrasive paper carefully for FSW experiments. Plates of 7075 aluminum alloy with a composition of Al-5.6Zn-2.5Mg-1.6Cu-0.23Cr (wt.%) were
SC
friction stir welded with the Zr51Ti5Ni10Cu25Al9 BMG at a welding speed of 100
M AN U
mm/min and a tool rotation speed of 800 rpm. The tool used had a shoulder 12 mm in diameter and a cylindrical pin 4 mm in diameter and 1.5 mm in length. During the FSW process, the BMG was put on the advance side and the 7075 alloy on the retreating side. The tool probe was offset into the 7075 alloy side with the lateral
TE D
surface of the probe slightly touching the BMG side. The welded samples were observed using scanning electron microscopy (SEM) on a polished cross-section etched by a solution of 30% HNO3 and 70% CH3OH. The distribution of chemical
EP
elements near the interface was determined by energy dispersive X-ray spectroscopy.
AC C
The phases were identified by micro-area X-ray diffractometry using Cu Kα radiation. The Vickers hardness profile of the weld was measured on the cross-section along the center line of the welded plate. The cross-sectional micrograph shown in Fig. 1 exhibits the microstructure of the
FSW BMG/aluminum alloy joint. As shown in Fig. 1(a), two different materials can be easily distinguished, namely the Zr51Ti5Ni10Cu25Al9 BMG on the lower side and the 7075 aluminum alloy on the upper side of the interface. However, some BMG
-3-
ACCEPTED MANUSCRIPT fragments with different sizes and irregular shapes are found distributed in the aluminum alloy side near the interface, indicating that parts of the BMG are shattered into tiny particles and stirred into the aluminum matrix during FSW process. Figure
RI PT
1(b) shows a typical magnified interface of FSW BMG/aluminum alloy joint. No weld defects can be detected along the weld interface, indicating that a sound welding was obtained between the BMG and aluminum alloy by FSW. However, some
SC
micro-voids can be observed around the large BMG fragments, which are shown in
the blocky BMG fragments [9].
M AN U
Fig. 1(c). The formation of the micro-voids might be related to the irregular shape of
Figure 2 shows the XRD patterns measured at the Zr51Ti5Ni10Cu25Al9 BMG, the 7075 aluminum alloy and the interface in the stir zone. As shown in curve (a), there is
TE D
a broaden peak in 2 theta region of 30~45° without any detectable crystalline Bragg peaks, indicating the amorphous structure of Zr51Ti5Ni10Cu25Al9 BMG. In contrast, the 7075 aluminum alloy is characterized by crystalline Bragg peaks shown in curve
EP
(c). For the BMG-7075 alloy interface, the XRD curve (b) exhibits a superimposition
AC C
of sharp peaks corresponding to the crystalline phase on the broad halo peak coming from the amorphous phase, indicating the existence of a mixture of the amorphous and some crystalline phases. The position and the intensity of the sharp crystalline peaks match exactly with that of Al. No other phases can be detected within the sensitivity limit of XRD, indicating that no chemical reaction took place between the two materials during the entire FSW process. Figure 3 shows the hardness profile of the BMG/aluminum alloy interface. The
-4-
ACCEPTED MANUSCRIPT zero point denotes the interface between the two materials. The left side exhibits the hardness of 7075 aluminum alloy. It can be seen that the hardness of 7075 aluminum alloy first decreases and then increases as the distance away from the weld interface.
RI PT
It has reported that the hardness of the aluminum alloy is mainly governed by the precipitates [10]. The precipitates in the nugget zone (NZ) and the heat affected zone (HAZ) will coarsen and/or dissolve, resulting in the reduced hardness [6]. The
SC
following increase of the hardness indicates that the hardness gradually approaches to
M AN U
the hardness of the base aluminum alloy. The right side illustrates the hardness of the Zr51Ti5Ni10Cu25Al9 BMG. Clearly, three different regions can be. The harness of BMG firstly increases as the position moves away from the weld interface. Then the hardness decreases and finally keeps constant at about 540 Hv. The evolution of the
TE D
hardness is closely related to the variation of free volume in the glassy alloy. Van den Beukel et al. [11] assumed that the change in the enthalpy upon structural relaxation is due to the variation of the free volume. Thus, it is reasonable to estimate the relative
EP
change in the free volume by the variation of the relaxation enthalpy (Hr) [12,13].
AC C
Figure 4 presents the thermograms of Zr51Ti5Ni10Cu25Al9 specimens with different distances away from the weld interface. The corresponding results of Hr versus the distances away from the weld interface are shown in the inset figure of Fig. 4. It is found that Hr first decreases and then increase with the distance moves away from the weld interface. According to the previous reports [14, 15], upon sub-Tg reheating, the excess free volume can be annihilated out of the metallic glass. When the sample is reheated to the temperature above Tg, the relaxed free volume in the bulk metallic
-5-
ACCEPTED MANUSCRIPT glasses can be restored. It has reported that the temperatures adjacent to NZ during the FSW procedure should be higher than Tg and lower than the crystallization temperature (Tx) [6]. Therefore, the relatively high Hr adjacent to the NZ can be
RI PT
ascribed to the recreation of the relaxed free volume induced by heating the sample above Tg. The first decrease of the Hr, indicating the reduction of the recreated free volume, is closely related to the decrease of temperature. Then it is reasonable to
SC
speculate that the reduction of the recreated free volume is the main reason for the
M AN U
first increase in the hardness of BMG. The following increase of the Hr, attributing to the increase of the free volume, induces the decrease of the hardness of BMG. When the temperature is lower than a certain value Tc, the heat may have a little influence on the free volume. Therefore, the hardnesses of BMG keep constant at about 540 Hv,
TE D
which coincides with the hardness of the as-cast Zr51Ti5Ni10Cu25Al9 BMG [16]. In summary, Zr51Ti5Ni10Cu25Al9 BMG were successfully friction stir welded to 7075 aluminum alloy. On the aluminum alloy side near the interface, some BMG
EP
fragments with irregular shapes and different sizes are found distributed in the nugget
AC C
zone. The hardness of 7075 aluminum alloy first decreases and then increases as the distance away from the weld interface. The harness of BMG firstly increases as the position moves away from the weld interface. Then the hardness decreases and keeps constant at about 540 Hv. The evolution of the hardness in the BMG side is closely related to the variation of free volume in the glassy alloy.
Acknowledgments This work was supported by the National Natural Science Foundation of China
-6-
ACCEPTED MANUSCRIPT (NSFC) under Grant Nos. 51401041 and 51025415.
References [1] Hu Z, Zhao ZQ, Wu YD, Lu T, Xing JS, Wei BC. Vacuum 2013;89:142-6.
2014;101:98-101. [3] Hua NB, Zhang T. J Alloys Compd 2014;602:339-45.
RI PT
[2] Tariq NH, Shakil M, Hasan BA, Akhter JI, Haq MA, Awan NA. Vacuum
M AN U
ZhaoYT, Wang J. Mater Lett 2007;61:2170-2.
SC
[4] Wang XY, Wang WK, Zhan ZJ, Xu FY, Zhang NY, Wang FX, ChenY, Pang LP,
[5] Liu X, Lan SH, Ni J. Mater Des 2014;59:50-62.
[6] Wang D, Xiao BL, Ma ZY, Zhang H.F. Scripta Mater 2009;60:112-5. [7] Ji YS, Fujii H, Sun Y.F, Maeda M, Nakata K, Kimura H, Inoue A, Nogi K. Mater
TE D
Trans 2009;50:1300-3.
[8] Qin ZX, Li CH, Zhang HF, Wang ZG, Hu ZQ, Liu Z.Q. J Mater Sci Technol 2009;25:853-6.
EP
[9] Sun Y, Ji Y, Fujii H, Nakata K, Nogi K. Mater Sci Eng A 2010;527:3427-32.
AC C
[10] Xie GM, Ma ZY, Geng L. J Mater Sci Technol 2009;25:351-5. [11] Van den Beukel A, Sietsma J. Acta Metall 1990;38:383-9. [12] Liu JW, Cao QP, Chen LY, Wang XD, Jiang JZ. Acta Mater 2010;58:4827-40. [13] Huang YJ, Sun Y, Shen J. Intermetallics 2010;18:2044-50. [14] Nagel C, Rätzke K, Schmidtke E,
Faupel F, Ulfert W. Phys Rev B
1999;60 :9212. [15] Nagel C, Rätzke K, Schmidtke E, Wolff J, Geyer U, Faupel F. Phys Rev B
-7-
ACCEPTED MANUSCRIPT 1998;57:10224. [16] Cao HB, Ma D, Hsieh KC, Ding L, Stratton WG, Voyles PM, Pan Y, Cai M,
RI PT
Dickinson JT, Chang YA. Acta Mater 2006;54:2975-82.
Figure captions
Fig. 1. SEM micrograph of the cross-section in the Zr51Ti5Ni10Cu25Al9 BMG/7075
SC
aluminum alloy.
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Fig. 2. X-ray diffraction patterns of (a) Zr51Ti5Ni10Cu25Al9 BMG, (b) cross-section of joint, (c) 7075 alloy.
Fig. 3. Hardness profile of the BMG/aluminum alloy interface. Fig. 4. Thermograms of Zr51Ti5Ni10Cu25Al9 specimens with different distances away
TE D
from the weld interface. The inset figure is the relaxation enthalpy Er versus the
AC C
EP
distances away from the weld interface.
-8-
ACCEPTED MANUSCRIPT
Fig. 1. SEM micrograph of the cross-section in the Zr51Ti5Ni10Cu25Al9
AC C
EP
TE D
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SC
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BMG/7075 aluminum alloy.
ACCEPTED MANUSCRIPT
Fig. 2. X-ray diffraction patterns of (a) Zr51Ti5Ni10Cu25Al9 BMG, (b) cross-
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TE D
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SC
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section of joint, (c) 7075 alloy.
ACCEPTED MANUSCRIPT
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TE D
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Fig. 3. Hardness profile of the BMG/aluminum alloy interface.
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Fig. 4. Thermograms of Zr51Ti5Ni10Cu25Al9 specimens with different distances away from the weld interface. The inset figure is the relaxation
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enthalpy Er versus the distances away from the weld interface.
ACCEPTED MANUSCRIPT 1. Zr51Ti5Ni10Cu25Al9 bulk metallic glass and 7075 aluminum alloy were successfully joined by friction stir welding. 2. The hardness of 7075 aluminum alloy first decreases and then increases as the
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distance away from the weld interface. 3. The evolution of the hardness in the BMG side is related to the variation of free
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volume.