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Research Papers

Cold Metal Transfer Joining of Aluminum AA6061-T6-to-Galvanized Boron Steel

[+] Author and Article Information
R. Cao

State Key Laboratory of Advanced Processing
and Recycling of Non-Ferrous Metals,
Lanzhou University of Technology,
Langongping 287 Road, Qilihe District,
Lanzhou 730050, China
e-mail: caorui@lut.cn

J. H. Sun

State Key Laboratory of Advanced Processing
and Recycling of Non-Ferrous Metals,
Lanzhou University of Technology,
Langongping 287 Road, Qilihe District,
Lanzhou 730050, China
e-mail: 1392672372@qq.com

J. H. Chen

State Key Laboratory of Advanced Processing
and Recycling of Non-Ferrous Metals,
Lanzhou University of Technology,
Langongping 287 Road, Qilihe District,
Lanzhou 730050, China
e-mail: zchen@lut.cn

Pei-Chung Wang

Manufacturing Systems Research Lab,
General Motors Global Research
and Development Center,
MC 480-106-RA2, 30500 Mound Road,
Warren, MI 48090
e-mail: peichung.wang@gmail.com

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received January 26, 2014; final manuscript received July 8, 2014; published online August 6, 2014. Assoc. Editor: Wayne Cai.

J. Manuf. Sci. Eng 136(5), 051015 (Aug 06, 2014) (10 pages) Paper No: MANU-14-1033; doi: 10.1115/1.4028012 History: Received January 26, 2014; Revised July 08, 2014

Along with the development of automobile industry for lightweight vehicles, more and more advanced and ultrahigh strength steels (e.g., hot stamping steel) have been used for automotive applications. Making use of the high strength steels not only reduces the vehicle weight and air emissions but also improves crash safety. Meanwhile, aluminum alloys are one of the lightest structural materials, and they have been widely used in automotive industry due to their many attractive properties such as low density, high specific strength along with good damping capacity. Since both hot stamping steel and aluminum alloys are being widely used for automotive applications, joining of hot stamping steel to aluminum alloys is inevitable. In this study, the feasibility of joining aluminum alloy AA6061-T6 to galvanized boron steel by cold metal transfer (CMT) method using AA4043 filler metal was investigated. The microstructures and chemical compositions of the welded lap joints were examined using scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS), while the static strengths of the joints were measured. Test results showed that a sound weld-brazed joint which consisted of rich zinc zone, reaction interface zone, weld metal zone and fusion zone was formed. The phases and thickness of the reaction layers were analyzed and identified. In addition, the strength of CMT weld-brazed aluminum AA6061-T6 to galvanized boron steel depends on the torch deviation (i.e., distance between the welding torch and the edge of the weld seam). The joints fabricated with a deviation distance of 2 mm had greater strength than that of the joints made a deviation distance of 0 mm. Finally, the effect of temperature exposure of hot stamping on the weldability of CMT joining of joining aluminum AA6061-T6 to galvanized boron steel was investigated. It was found that the surface of galvanized boron steel was severely oxidized after heat treatment process and consequently reduced the weldability in CMT joining AA6061-T6 and galvanized boron steel.

Copyright © 2014 by ASME
Topics: Joining , Steel , Aluminum , Metals , Welding
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References

Figures

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Fig. 3

Schematic of lapped aluminum-to-steel workpiece: (a) plane view, (b) side view of the welding torch with respect to the sample, and (c) specimen machined from the weld-brazed joint (dimensions in mm)

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Fig. 2

Schematic of a CMT welding-brazing of aluminum 6061-T6 to Al–Zn coated galvanized boron steel joint

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Fig. 1

Phase diagram of Al–Fe [16]

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Fig. 10

Microstructure and line scan analysis of at the brazing interface for CMT joined 1.0 mm thick AA6061-T6-1.0 mm thick galvanized boron steel (a) the brazing interface and (b) line scan analysis along yellow line shown in Fig.10(a).

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Fig. 8

Microstructure of CMT weld-brazed 1.0 mm thick AA6061-T6-1.0 mm thick galvanized boron steel

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Fig. 9

Microstructures of CMT weld-brazed 1.0 mm thick AA6061-T6-1.0 mm thick galvanized boron steel at: (a) zone A shown in Fig. 8; (b) enlarged zone A; (c) transition interface B; (d) middle interface C; (e) weld metal D; (f) weld root E; (g) fusion zone F; and (h) enlarged zone F

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Fig. 4

Microstructure and composition analysis of coating layer of galvanized boron steel: (a) microstructure, (b) higher magnification of the microstructure, (c) cross section of coating layer, (d) analysis of the coating layer, and (e) XRD analysis of the coating layer

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Fig. 5

Al–Zn binary phase diagram [20]

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Fig. 6

Effects of welding variables on the joint strength of CMT weld-brazed AA6061-T6 to galvanized boron steel without the interaction effects

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Fig. 7

Effect of the process variables on the weld appearance with: (a) a wire feed speed of 3.0 m/min, a current of 50 A, a voltage of 9.4 V, a deviation distance of 2 mm, and a correction of the arc length: −30%; (b) a wire feed speed of 4.0 m/min, a current of 71 A, and a voltage of 11.7 V, a deviation distance of 1 mm and a correction of the arc length:0%; (c) a wire feed speed: 5.0 m/min, I:95 A, U:13.4 V, deviation distance:2 mm and the correction of the arc length:0%; and (d) the optimized CMT joined AA6061-T6 to galvanized boron steel

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Fig. 11

Comparison of strengths of CMT weld-brazed 1.0 mm thick AA6061-T6-1.0 mm thick galvanized boron steel and CMT welded 1.0 mm thick AA6061-T6-to-1.0 mm thick AA6061-T6 specimens

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Fig. 12

Failure locations of CMT weld-brazed 1.0 mm thick AA6061-T6-1.0 mm thick galvanized boron steel at the: (a) aluminum heat-affected-zone and (b) weld metal

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Fig. 13

Fracture initiation at the weld root (E zone shown in Fig. 8) in CMT weld-brazed 1.0 mm thick AA6061-T6-1.0 mm thick galvanized boron steel

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Fig. 14

Fractography of CMT welded-brazed 1.0 mm thick AA6061-T6-1.0 mm thick galvanized boron steel: (a) fractured at the weld root metal (e.g., zone G in Fig. 12(b)) and (b) fracture surface of the weld metal

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Fig. 15

Effects of welding parameters on tensile strength of CMT weld-brazed 1.0 mm thick AA6061-T6-1.0 mm thick galvanized boron steel

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Fig. 16

Weld appearance of CMT weld-brazed AA6061-T6 and galvanized boron steel through the hot stamping process

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Fig. 17

Heat treated galvanized boron steel: (a) appearance and (b) component analytics of the coating before CMT joining (e.g., region A in Fig. 16(a))

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