- Email: [email protected]
A380 bimetallic castings by the zincate process followed with galvanizing
Accepted Manuscript Removing the oxide layer on the A380 substrate of AM60/A380 bimetallic castings by the zincate process followed with galvanizing Hui Zhang, Yiqing Chen, Alan A. Luo PII:
S0042-207X(17)31368-4
DOI:
10.1016/j.vacuum.2017.11.003
Reference:
VAC 7671
To appear in:
Vacuum
Received Date: 29 September 2017 Revised Date:
31 October 2017
Accepted Date: 2 November 2017
Please cite this article as: Zhang H, Chen Y, Luo AA, Removing the oxide layer on the A380 substrate of AM60/A380 bimetallic castings by the zincate process followed with galvanizing, Vacuum (2017), doi: 10.1016/j.vacuum.2017.11.003. 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 Removing the oxide layer on the A380 substrate of AM60/A380 bimetallic castings by the zincate process followed with galvanizing Hui Zhang a, *, Yiqing Chen b, and Alan A. Luo c The 38th Research Institute of China Electronics Technology Group Corporation,
b
RI PT
Hefei 230088, Anhui, China
School of Materials Science and Engineering, Hefei University of Technology, Hefei
230009, Anhui, China c
College of Engineering, The Ohio State University, Columbus 43210, OH, USA
*Corresponding author. Tel:/fax: +86 551 65391623.
M AN U
E-mail addresses: [email protected].
SC
a
Post address: P.O. Box 9023, No.199 Xiangzhang Street, Hefei 230088, Anhui, China.
Abstract
TE D
The bimetallic experiments in combination with “zincate + galvanizing” surface treatment of the A380 substrates were carried out. The effect of surface treatment on the interfacial microstructure and shear strength of AM60/A380 bimetallic castings was
EP
investigated. The results showed that the wetting between molten AM60 and A380
AC C
substrates with the “zincate + galvanizing” surface treatment was excellent. The “zincate + galvanizing” surface treatment removed the natural oxides on the A380 surfaces which were replaced by the zinc film. The “zincate + galvanizing” surface treatment could also improve the shear strength of AM60/A380 bimetallic castings. The bimetallic casting with the preheating time of 110s and substrate preheating temperature of 560°C had the optimal shear strength of 63.8 MPa.
Keywords
1
ACCEPTED MANUSCRIPT Bimetallic casting; Surface treatment; Interface structure; AM60; A380.
Magnesium (Mg) and aluminum (Al) alloys, which are regarded as the lightest structural metals for the light weighting and energy efficiency, have been wide
RI PT
applications in transportation industries [1-3]. Multi-material design and manufacturing instead of single metal, such as Mg/Al bimetallic systems, can be used to meet the complex engineering and the specific requirements in the transportation industries [4-6].
SC
However, the oxide layers and brittle intermetallic phases are easily formed in the interface. Many methods, such as fusion welding and solid-state joining methods, have
M AN U
been tried to create strong Mg/Al bimetallic structures with limited success [7-10]. Overcasting is a key enabling technology, which can be used for multi-material structures. It is reported that the Al-based and Mg-based light alloys can be cast around dissimilar material substrates using the overcasting process of molten Mg onto solid Al
TE D
substrate [11-13]. However, the nature oxide layer in the surface of the A380 substrate is hard to be wetted by molten Mg alloys and prohibits the necessary diffusion reaction [4]. During overcasting, the large solidification shrinkage results in a relatively strong
EP
mechanical bond/interlock at the interface of the current overcasting structures but that
AC C
relies on the “shrink-fit” between the casting layer and the substrate. In this paper, the bimetallic experiments in combination with “zincate + galvanizing” surface treatment on A380 substrates are carried out. The effect of the surface treatment on the interfacial microstructure and strength of AM60/A380 bimetallic castings are also discussed. The Mg alloy (AM60) with the chemical composition of Mg-6.0Al-0.35Mn (wt. %) and Al alloy (A380) are with the chemical composition of Al-8.2Si-3.6Cu-1.2Fe-1.6Zn (wt. %) used in this study. The zincate process with the zinc-galvanizing step was
2
ACCEPTED MANUSCRIPT applied to replace the oxide layer with a metallic zinc film of controllable thickness. Each step of the “zincate + galvanizing” process was listed in detail in Table.1. Table.1. Chemicals and conditions for “zincate + galvanizing” treatment. Chemicals and operating conditions
Degrease
C3H5O, ultrasonic cleaning for 5 min
Alkali etching
NaOH, NaF, 60-80°C, 5-10 s
Pickling
(50%) HNO3, (40%) HF, 5-10 s
Zincate
NaOH, ZnO, KNaC4H4O6·4H2O, FeCl3·6H2O, 18-25°C,
immersion
60 s (first immersion), 30 s (second immersion)
Zinc galvanizing
KCl, ZnCl3, HBO3, 0.5-5 A/dm2, 20-45 °C, 15-25 min
M AN U
SC
RI PT
Procedure
The quartz tube chamber was placed in the electric resistance furnace. The vacuum level of the quartz tube chamber was reduced to approximately 5×10-3 Pa. Next, the
TE D
quartz tube chamber was filled with argon gas (99.99 % Ar) and the pressure was maintained about 1.2 atmospheres. Then, the electric resistance furnace was heated to the temperature of 700°C.
EP
The A380 alloy substrate with the size of 20 mm x 15 mm x 3 mm was previously
AC C
placed beneath the outlet of the syringe in the quartz tube chamber and then preheated by the controlled time. Fig.1a shows the substrate temperature with increasing preheating time at furnace temperature of 700°C. According to Fig.1a, when the A380 substrate was advisable preheated with the time ranging from 100s to 130s, the corresponding temperature of the A380 substrate ranged from 500°C to 600°C. The solidus temperature of A380 alloy is about 580°C. Molten AM60 alloy was dropped onto the A380 alloy substrate operated by the graphite plunger. After the wetting experiment, the bimetallic sample was placed into the low temperature zone and cooled
3
ACCEPTED MANUSCRIPT down. During the process, the molten AM60 alloy droplet was free of oxide. The Scanning Electron Microscope (SEM) couple with energy dispersive spectroscopy (EDS), the electron probe micro-analyzer (EPMA) and X-ray diffraction (XRD) were used to examine the microstructure of the bimetallic samples. The shear
RI PT
tests were carried out, using an MTS809 mechanical testing machine.
It is reported that the oxide layer can be removed by the conventional zincate process [7]. At the same time, the zinc film is formed with the thickness of 200-300 nm during
SC
the process, which is not sufficient for interfacial bonding. However, the thin zinc film of 200-300 nm on the A380 substrate would evaporate fast when the A380 substrate is
M AN U
heated during the bimetallic experiments, resulting in the re-oxidation of the A380 substrate before contacting with the molten AM60 alloy. Therefore, the zincate process followed by galvanizing is used in this study. The oxide layer has been removed by the “zincate + galvanizing” surface treatment. The thickness of the zinc film is increased to
TE D
5-6µm, as shown in Fig.1b. The zinc film can completely cover the aluminum alloy (Fig.1b). Compared with the melting temperature of Al element (660ºC), the melting temperature of zinc is lower (419ºC). The zinc film can prevent the A380 substrate from
EP
re-oxidation, which is also beneficial to promote the wetting and the metallurgical bond
AC C
between the A380 substrate and the overcast AM60 alloy. Fig.1c and 1d shows the macro-morphologies of the interfacial wetting between AM60 and A380 substrate with and without the “zincate + galvanizing” treatment each. It shows that the interfacial wetting between the AM60 and A380 substrate with the “zincate + galvanizing” treatment is better by removing the natural Al2O3 layer on the aluminum alloy substrate, compared with that without the “zincate + galvanizing” treatment, which indicates that the zinc film with the “zincate + galvanizing” treatment can significantly enhance the wetting properties.
4
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.1. (a) Substrate temperature with increasing preheating time at furnace temperature of 700°C, (b) SEM image of the cross-section of the sample with the thickness of zinc layer of 5-6µm, Interfacial wetting between AM60 alloy and A380 substrate: (c) without
TE D
and (d) with the “zincate + galvanizing” treatment (Furnace temperature of 700°C and substrate preheating temperature of 560°C).
EP
Fig.2a shows the interfacial microstructure of the AM60/A380 bimetallic sample with the furnace temperature of 700°C and substrate preheating temperature of 560°C. The
AC C
metallurgical reaction zone between molten AM60 and A380 substrate is shown. The distributions of Al, Mg and Si in the reaction zone of the bimetallic interfaces are also shown in Fig.2a.
Quantitative analysis results of Al, Mg and Si concentrations by EPMA for the different spots (A1-A6 in Fig.2a) are listed in Table.2. Combining the XRD analysis (Fig.2b) with the results of EPMA (Table.2), it is considered that the layer I (A1-A3) next to the A380 substrate consists of the Al3Mg2 and Mg2Si intermetallic compounds. The layer II (A4-A6) is the solidification product of Mg-Al alloy melt. The main 5
ACCEPTED MANUSCRIPT constituent is the lamellar structure, which is the result of the eutectic transformation at 437°C (L→Al12Mg17 +α-Mg). Some rod-like primary α-Mg phase is also observed, as
AC C
EP
TE D
M AN U
SC
RI PT
shown in Fig.2c.
Fig.2. (a) SEM image with EDS line scans of AM60/A380 bimetallic sample (Furnace temperature of 700°C and substrate preheating temperature of 560°C), (b) XRD patterns of the constituent phases on the Al side and (c) SEM image of the eutectic region of
6
ACCEPTED MANUSCRIPT zone “A” in Fig.2a.
Table.2. The results of EPMA quantitative analysis for the spots marked as A1-A6 in
Area
Element compositions (wt. %)
RI PT
Fig.2a.
Interface component Al
Mg
Si
A1
60.47
34.42
5.13
Al3Mg2+Mg2Si
A2
58.56
35.72
5.71
Al3Mg2+Mg2Si
A3
59.32
36.55
4.15
A4
55.95
44.72
0.67
A5
58.77
39.53
1.72
Al12Mg17 +α-Mg
A6
67.22
31.86
0.92
Al12Mg17 +α-Mg
SC
number
Al3Mg2+Mg2Si
M AN U
Al12Mg17 +α-Mg
TE D
Fig.3a shows the shear strengths of AM60/A380 bimetallic samples with the different substrate preheating times. The shear strength increases with increasing preheating time from 90s to 110s and then decreases with increasing preheating time from 110s to 130s.
EP
The bimetallic sample with the preheating time of 110s and substrate preheating
AC C
temperature of 560°C has the peak shear strength of 63.8MPa. As the preheating time increases, the increasing preheating temperature leads to the excessive melting of the aluminum alloy substrate and the formation of large amount of brittle intermetallic particles with prolonged preheating time, which would decrease the shear strength. Fig.3b shows the fracture surface of the AM60/A380 bimetallic casting with the furnace temperature of 700°C and substrate preheating temperature of 560°C. There are mostly quasi-cleavage fracture with very few dimples. The main failure mechanism of the bimetallic sample is the intergranular fracture feature and the crack originated from
7
ACCEPTED MANUSCRIPT
RI PT
the intermetallic particles.
SC
Fig.3. (a) The shear strengths of AM60/A380 bimetallic samples with the different substrate preheating times (Furnace temperature of 700°C) and (b) micrograph of
M AN U
fracture surface after shear strength test (Furnace temperature of 700°C and substrate preheating temperature of 560°C).
The oxide layer can be removed and the metallic zinc film forms on the A380
TE D
substrate by the “zincate + galvanizing” surface treatment. The bimetallic samples with “zincate + galvanizing” surface treatment show excellent wettability, compared with that without the surface treatment. The improved wetting by removing the natural Al2O3
EP
layer on the A380 substrate provides the enhanced metallurgical bond in the bimetallic samples. The preheating temperature and time of the substrate have the effect on the
AC C
shear strength of the Al/Mg bimetallic casting. The prolonged preheating leads to the excessive melting of the A380 substrate and the formation of large amount of brittle intermetallic particles, resulting in the reduction in the shear strength. This work was supported by the National Natural Science Foundation of China [grant number 51571080].
References [1] A.I. Taub, P.E. Krajewski, A.A. Luo, and J.N. Owens, The evolution of technology 8
ACCEPTED MANUSCRIPT for materials processing over the last 50 years: The automotive example, JOM 59 (2007) 48-57. [2] J. Shang, K.H. Wang, Q. Zhou, D.K. Zhang, J. Huang, J.Q. Ge, Effect of joining temperature on microstructure and properties of diffusion bonded Mg/Al joints, Trans.
RI PT
Nonferrous Met. Soc. China 22 (2012) 1961-1966.
[3] Z.L. Liu, Y. Liu, X.Q. Liu, M.M. Wang, Effect of Minor Zn Additions on the Mechanical and Corrosion Properties of Solution - Treated AM60 - 2%RE Magnesium
SC
Alloy, J. Mater. Eng. Perform. 25 (2016) 2855-2865.
[4] K.J.M. Papis, J.F. Löffler, P.J. Uggowitzer, Interface formation between liquid and
M AN U
solid Mg alloys - An approach to continuously metallurgic joining of magnesium parts, Mater. Sci. Eng. A 527 (2010) 2274-2279.
[5] T. Wróbel, Characterization of bimetallic castings with an austenitic working surface layer and an unalloyed cast steel base, J. Mater. Eng. Perform. 23 (2014) 1711-1717.
TE D
[6] S.A. Zhou, Z. Zhang, M. Li, D.J. Pan, H.L. Su, X.D. Du, P. Li, Y.C. Wu, Correlative characterization of primary particles formed in as-cast Al-Mg alloy containing a high level of Sc, Mater. Charact. 118 (2016) 85-91.
EP
[7] K.J.M. Papis, B. Hallstedt, J.F. Löffler, P.J. Uggowitzer, Interface formation in
AC C
aluminium-aluminium compound casting, Acta Mater. 56 (2008) 3036-3043. [8] L.M. Zhao, Z.D. Zhang, Effect of Zn alloy interlayer on interface microstructure and strength of diffusion-bonded Mg-Al joints, Scr. Mater. 5 (2008) 283-286. [9] P. Liu, Y.J. Li, H.R. Geng, J. Wang, Investigation of interfacial structure of Mg/Al vacuum diffusion-bonded joint, Vacuum 80 (2006) 395-399. [10] K. He, J.H. Zhao, P. Li, J.S. He, Q. Tang, Investigation on microstructures and properties of arc-sprayed-Al/AZ91D bimetallic material by solid-liquid compound casting, Mater. Des. 112 (2016) 553-564.
9
ACCEPTED MANUSCRIPT [11] W.M. Jiang, G.Y. Li, Z.T. Fan, L. Wang, F.C. Liu, Investigation on the interface characteristics of Al/Mg bimetallic castings processed by lost foam casting, Metall. Mater. Trans. A 47 (2016) 2462-2470. [12] R. Mola, T. Bucki, A. Dziadoń, Formation of Al-alloyed layer on magnesium with
RI PT
use of casting techniques, Arch. Found. Eng. 16 (2016) 112-116.
[13] R. Mola, T. Bucki, A. Dziadoń, Microstructure of the bonding zone between AZ91
AC C
EP
TE D
M AN U
SC
and AlSi17 formed by compound casting, Arch. Found. Eng. 17 (2017) 202-206.
10
ACCEPTED MANUSCRIPT Figure captions Fig.1. (a) Substrate temperature with increasing preheating time at furnace temperature of 700°C, (b) SEM image of the cross-section of the sample with the thickness of zinc layer of 5-6µm, Interfacial wetting between AM60 alloy and A380
RI PT
substrate: (c) without and (d) with the “zincate + galvanizing” treatment (Furnace temperature of 700°C and substrate preheating temperature of 560°C).
Fig.2. (a) SEM image with EDS line scans of AM60/A380 bimetallic sample (Furnace
SC
temperature of 700°C and substrate preheating temperature of 560°C), (b) XRD
region of zone “A” in Fig.2a.
M AN U
patterns of the constituent phases on the Al side and (c) SEM image of the eutectic
Fig.3. (a) The shear strengths of AM60/A380 bimetallic samples with the different substrate preheating times (Furnace temperature of 700°C) and (b) micrograph of fracture surface after shear strength test (Furnace temperature of 700°C and substrate
AC C
EP
TE D
preheating temperature of 560°C).
11
ACCEPTED MANUSCRIPT Table captions Table.1. Chemicals and conditions for “zincate + galvanizing” treatment. Table.2. The results of EPMA quantitative analysis for the spots marked as A1-A6 in
AC C
EP
TE D
M AN U
SC
RI PT
Fig.2a.
12
ACCEPTED MANUSCRIPT Highlights 1: The “zincate + galvanizing” surface treatment removes the natural oxides on the A380 surfaces which are replaced by zinc film.
galvanizing” surface treatment is excellent.
RI PT
2: The wetting between molten AM60 and A380 substrates with the “zincate +
decreases with increasing the preheating time.
SC
3: The shear strength of the AM60/A380 bimetallic casting increases and then
M AN U
4: The prolonged preheating leads to the excessive melting of A380 substrate and the formation of brittle intermetallic particles, resulting in the reduction in shear
AC C
EP
TE D
strength.
S0042-207X(17)31368-4
DOI:
10.1016/j.vacuum.2017.11.003
Reference:
VAC 7671
To appear in:
Vacuum
Received Date: 29 September 2017 Revised Date:
31 October 2017
Accepted Date: 2 November 2017
Please cite this article as: Zhang H, Chen Y, Luo AA, Removing the oxide layer on the A380 substrate of AM60/A380 bimetallic castings by the zincate process followed with galvanizing, Vacuum (2017), doi: 10.1016/j.vacuum.2017.11.003. 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 Removing the oxide layer on the A380 substrate of AM60/A380 bimetallic castings by the zincate process followed with galvanizing Hui Zhang a, *, Yiqing Chen b, and Alan A. Luo c The 38th Research Institute of China Electronics Technology Group Corporation,
b
RI PT
Hefei 230088, Anhui, China
School of Materials Science and Engineering, Hefei University of Technology, Hefei
230009, Anhui, China c
College of Engineering, The Ohio State University, Columbus 43210, OH, USA
*Corresponding author. Tel:/fax: +86 551 65391623.
M AN U
E-mail addresses: [email protected].
SC
a
Post address: P.O. Box 9023, No.199 Xiangzhang Street, Hefei 230088, Anhui, China.
Abstract
TE D
The bimetallic experiments in combination with “zincate + galvanizing” surface treatment of the A380 substrates were carried out. The effect of surface treatment on the interfacial microstructure and shear strength of AM60/A380 bimetallic castings was
EP
investigated. The results showed that the wetting between molten AM60 and A380
AC C
substrates with the “zincate + galvanizing” surface treatment was excellent. The “zincate + galvanizing” surface treatment removed the natural oxides on the A380 surfaces which were replaced by the zinc film. The “zincate + galvanizing” surface treatment could also improve the shear strength of AM60/A380 bimetallic castings. The bimetallic casting with the preheating time of 110s and substrate preheating temperature of 560°C had the optimal shear strength of 63.8 MPa.
Keywords
1
ACCEPTED MANUSCRIPT Bimetallic casting; Surface treatment; Interface structure; AM60; A380.
Magnesium (Mg) and aluminum (Al) alloys, which are regarded as the lightest structural metals for the light weighting and energy efficiency, have been wide
RI PT
applications in transportation industries [1-3]. Multi-material design and manufacturing instead of single metal, such as Mg/Al bimetallic systems, can be used to meet the complex engineering and the specific requirements in the transportation industries [4-6].
SC
However, the oxide layers and brittle intermetallic phases are easily formed in the interface. Many methods, such as fusion welding and solid-state joining methods, have
M AN U
been tried to create strong Mg/Al bimetallic structures with limited success [7-10]. Overcasting is a key enabling technology, which can be used for multi-material structures. It is reported that the Al-based and Mg-based light alloys can be cast around dissimilar material substrates using the overcasting process of molten Mg onto solid Al
TE D
substrate [11-13]. However, the nature oxide layer in the surface of the A380 substrate is hard to be wetted by molten Mg alloys and prohibits the necessary diffusion reaction [4]. During overcasting, the large solidification shrinkage results in a relatively strong
EP
mechanical bond/interlock at the interface of the current overcasting structures but that
AC C
relies on the “shrink-fit” between the casting layer and the substrate. In this paper, the bimetallic experiments in combination with “zincate + galvanizing” surface treatment on A380 substrates are carried out. The effect of the surface treatment on the interfacial microstructure and strength of AM60/A380 bimetallic castings are also discussed. The Mg alloy (AM60) with the chemical composition of Mg-6.0Al-0.35Mn (wt. %) and Al alloy (A380) are with the chemical composition of Al-8.2Si-3.6Cu-1.2Fe-1.6Zn (wt. %) used in this study. The zincate process with the zinc-galvanizing step was
2
ACCEPTED MANUSCRIPT applied to replace the oxide layer with a metallic zinc film of controllable thickness. Each step of the “zincate + galvanizing” process was listed in detail in Table.1. Table.1. Chemicals and conditions for “zincate + galvanizing” treatment. Chemicals and operating conditions
Degrease
C3H5O, ultrasonic cleaning for 5 min
Alkali etching
NaOH, NaF, 60-80°C, 5-10 s
Pickling
(50%) HNO3, (40%) HF, 5-10 s
Zincate
NaOH, ZnO, KNaC4H4O6·4H2O, FeCl3·6H2O, 18-25°C,
immersion
60 s (first immersion), 30 s (second immersion)
Zinc galvanizing
KCl, ZnCl3, HBO3, 0.5-5 A/dm2, 20-45 °C, 15-25 min
M AN U
SC
RI PT
Procedure
The quartz tube chamber was placed in the electric resistance furnace. The vacuum level of the quartz tube chamber was reduced to approximately 5×10-3 Pa. Next, the
TE D
quartz tube chamber was filled with argon gas (99.99 % Ar) and the pressure was maintained about 1.2 atmospheres. Then, the electric resistance furnace was heated to the temperature of 700°C.
EP
The A380 alloy substrate with the size of 20 mm x 15 mm x 3 mm was previously
AC C
placed beneath the outlet of the syringe in the quartz tube chamber and then preheated by the controlled time. Fig.1a shows the substrate temperature with increasing preheating time at furnace temperature of 700°C. According to Fig.1a, when the A380 substrate was advisable preheated with the time ranging from 100s to 130s, the corresponding temperature of the A380 substrate ranged from 500°C to 600°C. The solidus temperature of A380 alloy is about 580°C. Molten AM60 alloy was dropped onto the A380 alloy substrate operated by the graphite plunger. After the wetting experiment, the bimetallic sample was placed into the low temperature zone and cooled
3
ACCEPTED MANUSCRIPT down. During the process, the molten AM60 alloy droplet was free of oxide. The Scanning Electron Microscope (SEM) couple with energy dispersive spectroscopy (EDS), the electron probe micro-analyzer (EPMA) and X-ray diffraction (XRD) were used to examine the microstructure of the bimetallic samples. The shear
RI PT
tests were carried out, using an MTS809 mechanical testing machine.
It is reported that the oxide layer can be removed by the conventional zincate process [7]. At the same time, the zinc film is formed with the thickness of 200-300 nm during
SC
the process, which is not sufficient for interfacial bonding. However, the thin zinc film of 200-300 nm on the A380 substrate would evaporate fast when the A380 substrate is
M AN U
heated during the bimetallic experiments, resulting in the re-oxidation of the A380 substrate before contacting with the molten AM60 alloy. Therefore, the zincate process followed by galvanizing is used in this study. The oxide layer has been removed by the “zincate + galvanizing” surface treatment. The thickness of the zinc film is increased to
TE D
5-6µm, as shown in Fig.1b. The zinc film can completely cover the aluminum alloy (Fig.1b). Compared with the melting temperature of Al element (660ºC), the melting temperature of zinc is lower (419ºC). The zinc film can prevent the A380 substrate from
EP
re-oxidation, which is also beneficial to promote the wetting and the metallurgical bond
AC C
between the A380 substrate and the overcast AM60 alloy. Fig.1c and 1d shows the macro-morphologies of the interfacial wetting between AM60 and A380 substrate with and without the “zincate + galvanizing” treatment each. It shows that the interfacial wetting between the AM60 and A380 substrate with the “zincate + galvanizing” treatment is better by removing the natural Al2O3 layer on the aluminum alloy substrate, compared with that without the “zincate + galvanizing” treatment, which indicates that the zinc film with the “zincate + galvanizing” treatment can significantly enhance the wetting properties.
4
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Fig.1. (a) Substrate temperature with increasing preheating time at furnace temperature of 700°C, (b) SEM image of the cross-section of the sample with the thickness of zinc layer of 5-6µm, Interfacial wetting between AM60 alloy and A380 substrate: (c) without
TE D
and (d) with the “zincate + galvanizing” treatment (Furnace temperature of 700°C and substrate preheating temperature of 560°C).
EP
Fig.2a shows the interfacial microstructure of the AM60/A380 bimetallic sample with the furnace temperature of 700°C and substrate preheating temperature of 560°C. The
AC C
metallurgical reaction zone between molten AM60 and A380 substrate is shown. The distributions of Al, Mg and Si in the reaction zone of the bimetallic interfaces are also shown in Fig.2a.
Quantitative analysis results of Al, Mg and Si concentrations by EPMA for the different spots (A1-A6 in Fig.2a) are listed in Table.2. Combining the XRD analysis (Fig.2b) with the results of EPMA (Table.2), it is considered that the layer I (A1-A3) next to the A380 substrate consists of the Al3Mg2 and Mg2Si intermetallic compounds. The layer II (A4-A6) is the solidification product of Mg-Al alloy melt. The main 5
ACCEPTED MANUSCRIPT constituent is the lamellar structure, which is the result of the eutectic transformation at 437°C (L→Al12Mg17 +α-Mg). Some rod-like primary α-Mg phase is also observed, as
AC C
EP
TE D
M AN U
SC
RI PT
shown in Fig.2c.
Fig.2. (a) SEM image with EDS line scans of AM60/A380 bimetallic sample (Furnace temperature of 700°C and substrate preheating temperature of 560°C), (b) XRD patterns of the constituent phases on the Al side and (c) SEM image of the eutectic region of
6
ACCEPTED MANUSCRIPT zone “A” in Fig.2a.
Table.2. The results of EPMA quantitative analysis for the spots marked as A1-A6 in
Area
Element compositions (wt. %)
RI PT
Fig.2a.
Interface component Al
Mg
Si
A1
60.47
34.42
5.13
Al3Mg2+Mg2Si
A2
58.56
35.72
5.71
Al3Mg2+Mg2Si
A3
59.32
36.55
4.15
A4
55.95
44.72
0.67
A5
58.77
39.53
1.72
Al12Mg17 +α-Mg
A6
67.22
31.86
0.92
Al12Mg17 +α-Mg
SC
number
Al3Mg2+Mg2Si
M AN U
Al12Mg17 +α-Mg
TE D
Fig.3a shows the shear strengths of AM60/A380 bimetallic samples with the different substrate preheating times. The shear strength increases with increasing preheating time from 90s to 110s and then decreases with increasing preheating time from 110s to 130s.
EP
The bimetallic sample with the preheating time of 110s and substrate preheating
AC C
temperature of 560°C has the peak shear strength of 63.8MPa. As the preheating time increases, the increasing preheating temperature leads to the excessive melting of the aluminum alloy substrate and the formation of large amount of brittle intermetallic particles with prolonged preheating time, which would decrease the shear strength. Fig.3b shows the fracture surface of the AM60/A380 bimetallic casting with the furnace temperature of 700°C and substrate preheating temperature of 560°C. There are mostly quasi-cleavage fracture with very few dimples. The main failure mechanism of the bimetallic sample is the intergranular fracture feature and the crack originated from
7
ACCEPTED MANUSCRIPT
RI PT
the intermetallic particles.
SC
Fig.3. (a) The shear strengths of AM60/A380 bimetallic samples with the different substrate preheating times (Furnace temperature of 700°C) and (b) micrograph of
M AN U
fracture surface after shear strength test (Furnace temperature of 700°C and substrate preheating temperature of 560°C).
The oxide layer can be removed and the metallic zinc film forms on the A380
TE D
substrate by the “zincate + galvanizing” surface treatment. The bimetallic samples with “zincate + galvanizing” surface treatment show excellent wettability, compared with that without the surface treatment. The improved wetting by removing the natural Al2O3
EP
layer on the A380 substrate provides the enhanced metallurgical bond in the bimetallic samples. The preheating temperature and time of the substrate have the effect on the
AC C
shear strength of the Al/Mg bimetallic casting. The prolonged preheating leads to the excessive melting of the A380 substrate and the formation of large amount of brittle intermetallic particles, resulting in the reduction in the shear strength. This work was supported by the National Natural Science Foundation of China [grant number 51571080].
References [1] A.I. Taub, P.E. Krajewski, A.A. Luo, and J.N. Owens, The evolution of technology 8
ACCEPTED MANUSCRIPT for materials processing over the last 50 years: The automotive example, JOM 59 (2007) 48-57. [2] J. Shang, K.H. Wang, Q. Zhou, D.K. Zhang, J. Huang, J.Q. Ge, Effect of joining temperature on microstructure and properties of diffusion bonded Mg/Al joints, Trans.
RI PT
Nonferrous Met. Soc. China 22 (2012) 1961-1966.
[3] Z.L. Liu, Y. Liu, X.Q. Liu, M.M. Wang, Effect of Minor Zn Additions on the Mechanical and Corrosion Properties of Solution - Treated AM60 - 2%RE Magnesium
SC
Alloy, J. Mater. Eng. Perform. 25 (2016) 2855-2865.
[4] K.J.M. Papis, J.F. Löffler, P.J. Uggowitzer, Interface formation between liquid and
M AN U
solid Mg alloys - An approach to continuously metallurgic joining of magnesium parts, Mater. Sci. Eng. A 527 (2010) 2274-2279.
[5] T. Wróbel, Characterization of bimetallic castings with an austenitic working surface layer and an unalloyed cast steel base, J. Mater. Eng. Perform. 23 (2014) 1711-1717.
TE D
[6] S.A. Zhou, Z. Zhang, M. Li, D.J. Pan, H.L. Su, X.D. Du, P. Li, Y.C. Wu, Correlative characterization of primary particles formed in as-cast Al-Mg alloy containing a high level of Sc, Mater. Charact. 118 (2016) 85-91.
EP
[7] K.J.M. Papis, B. Hallstedt, J.F. Löffler, P.J. Uggowitzer, Interface formation in
AC C
aluminium-aluminium compound casting, Acta Mater. 56 (2008) 3036-3043. [8] L.M. Zhao, Z.D. Zhang, Effect of Zn alloy interlayer on interface microstructure and strength of diffusion-bonded Mg-Al joints, Scr. Mater. 5 (2008) 283-286. [9] P. Liu, Y.J. Li, H.R. Geng, J. Wang, Investigation of interfacial structure of Mg/Al vacuum diffusion-bonded joint, Vacuum 80 (2006) 395-399. [10] K. He, J.H. Zhao, P. Li, J.S. He, Q. Tang, Investigation on microstructures and properties of arc-sprayed-Al/AZ91D bimetallic material by solid-liquid compound casting, Mater. Des. 112 (2016) 553-564.
9
ACCEPTED MANUSCRIPT [11] W.M. Jiang, G.Y. Li, Z.T. Fan, L. Wang, F.C. Liu, Investigation on the interface characteristics of Al/Mg bimetallic castings processed by lost foam casting, Metall. Mater. Trans. A 47 (2016) 2462-2470. [12] R. Mola, T. Bucki, A. Dziadoń, Formation of Al-alloyed layer on magnesium with
RI PT
use of casting techniques, Arch. Found. Eng. 16 (2016) 112-116.
[13] R. Mola, T. Bucki, A. Dziadoń, Microstructure of the bonding zone between AZ91
AC C
EP
TE D
M AN U
SC
and AlSi17 formed by compound casting, Arch. Found. Eng. 17 (2017) 202-206.
10
ACCEPTED MANUSCRIPT Figure captions Fig.1. (a) Substrate temperature with increasing preheating time at furnace temperature of 700°C, (b) SEM image of the cross-section of the sample with the thickness of zinc layer of 5-6µm, Interfacial wetting between AM60 alloy and A380
RI PT
substrate: (c) without and (d) with the “zincate + galvanizing” treatment (Furnace temperature of 700°C and substrate preheating temperature of 560°C).
Fig.2. (a) SEM image with EDS line scans of AM60/A380 bimetallic sample (Furnace
SC
temperature of 700°C and substrate preheating temperature of 560°C), (b) XRD
region of zone “A” in Fig.2a.
M AN U
patterns of the constituent phases on the Al side and (c) SEM image of the eutectic
Fig.3. (a) The shear strengths of AM60/A380 bimetallic samples with the different substrate preheating times (Furnace temperature of 700°C) and (b) micrograph of fracture surface after shear strength test (Furnace temperature of 700°C and substrate
AC C
EP
TE D
preheating temperature of 560°C).
11
ACCEPTED MANUSCRIPT Table captions Table.1. Chemicals and conditions for “zincate + galvanizing” treatment. Table.2. The results of EPMA quantitative analysis for the spots marked as A1-A6 in
AC C
EP
TE D
M AN U
SC
RI PT
Fig.2a.
12
ACCEPTED MANUSCRIPT Highlights 1: The “zincate + galvanizing” surface treatment removes the natural oxides on the A380 surfaces which are replaced by zinc film.
galvanizing” surface treatment is excellent.
RI PT
2: The wetting between molten AM60 and A380 substrates with the “zincate +
decreases with increasing the preheating time.
SC
3: The shear strength of the AM60/A380 bimetallic casting increases and then
M AN U
4: The prolonged preheating leads to the excessive melting of A380 substrate and the formation of brittle intermetallic particles, resulting in the reduction in shear
AC C
EP
TE D
strength.