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Research Papers

Weldability and Distortion of Mg AZ31-to-Galvanized Steel SPOT Plug Welding Joint by Cold Metal Transfer Method

[+] 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 730050, China
e-mail: caorui@lut.cn

Q. W. Xu

State Key Laboratory of Advanced Processing
and Recycling of Non-ferrous Metals,
Lanzhou University of Technology,
Langongping 287 Road,
Qilihe District 730050, China
e-mail: 576832383@qq.com

H. X. Zhu

State Key Laboratory of Advanced Processing
and Recycling of Non-ferrous Metals,
Lanzhou University of Technology,
Langongping 287 Road,
Qilihe District 730050, China
e-mail: 1060870005@qq.com

G. J. Mao

State Key Laboratory of Advanced Processing
and Recycling of Non-ferrous Metals,
Lanzhou University of Technology,
Langongping 287 Road,
Qilihe District 730050, China
e-mail: 992947619@qq.com

Q. Lin

State Key Laboratory of Advanced Processing
and Recycling of Non-ferrous Metals,
Lanzhou University of Technology,
Langongping 287 Road,
Qilihe District 730050, China
e-mail: lqllinqiaoli@163.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 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: pei-chung.wang@gm.com

Manuscript received January 28, 2016; final manuscript received June 12, 2016; published online August 24, 2016. Assoc. Editor: Wayne Cai.

J. Manuf. Sci. Eng 139(2), 021001 (Aug 24, 2016) (11 pages) Paper No: MANU-16-1070; doi: 10.1115/1.4034009 History: Received January 28, 2016; Revised June 12, 2016

In this study, cold metal transfer (CMT) plug welding of 1 mm thick Mg AZ31 to 1 mm thick hot-dipped galvanized mild steel (i.e., Q235) was studied. Welding tests were performed and the process variables optimized with Mg AZ61 wire and 100% argon shielding gas for a plug weld located in the center of the 25 mm overlap region. It was found that it is feasible to join 1 mm thick Mg AZ31 workpiece to 1 mm thick galvanized mild steel using CMT plug welding. The optimized process variables for CMT plug welding Mg AZ31-to-galvanized mild steel were a wire feed speed of 10.5 m/min, a predrilled hole with a diameter of 8 mm in Mg AZ31 workpiece and a welding time of 0.8 s. CMT plug welded Mg AZ31-to-galvanized mild steel joints were composed of the fusion zone between Mg AZ31 base metal and Mg weld metal, Mg weld metal (i.e., combined base metal, filler wire and Zn coating), and the brazing interface between magnesium weld metal and galvanized mild steel. The brazing interface mainly consisted of Al, Zn, Mg, Si intermetallic compounds and oxides (i.e., Fe3Al, Mg2Si, MgZn, and MgZn2), and magnesium solid solution. The static strength of CMT welded-brazed Mg AZ31-galvanized steel was determined primarily by the strength and area of the brazed interface and thickness of the intermetallic reaction layer.

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References

Figures

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Fig. 1

Phase diagram of Mg-Fe [6]

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Fig. 2

Schematic of: (a) Mg AZ31-galvanized steel and (b) galvanized steel-Mg AZ31 joints (dimensions in mm)

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Fig. 3

Effect of welding variable on the strength for CMT plug welded 1 mm thick Mg AZ31-to-1 mm thick galvanized steel

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Fig. 5

(a) Appearance and (b) cross sections of the optimized CMT plug welded Mg AZ31-galvanized steel shown in Fig. 2(a)

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Fig. 6

(a) Appearance and (b) cross sections of the optimized CMT plug welded 1 mm thick galvanized steel-1 mm thick Mg AZ31 shown in Fig. 2(b)

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Fig. 9

Line analyses of various interfaces for optimized plug welded Mg AZ31-to-galvanized steel along the red line in (a) Fig. 8(a), (b) Fig. 8(b), (c) Fig. 8(c), and (d) Fig. 8(d)

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Fig. 10

X-ray analysis at the brazed galvanized steel/Mg AZ31 weld metal interface

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Fig. 11

Comparison of the quasi-static force–displacement of CMT plug weld-brazed 1 mm thick Mg AZ31–1 mm thick galvanized steel, and 1 mm thick galvanized steel-1 mm thick Mg AZ31, and 1 mm thick Mg AZ31-1 mm thick Mg AZ31

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Fig. 12

(a) Schematic of fracture locations, (b) fractured surfaces of Mg AZ31-galvanized steel brazing interface in region A of subfigure, (c) fractured surfaces of Mg AZ31-galvanized steel brazing interface in region B of subfigure of CMT plug welded 1 mm thick Mg AZ31B-to-1 mm thick galvanized mild steel joint at a wire speed of 10.5 m/min, a welding time of 0.8 s and a hole with a diameter of 8.0 mm in Mg AZ31

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Fig. 13

Fracture surfaces of CMT plug welded 1 mm thick galvanized mild steel-to-1 mm thick Mg AZ31 B joint at a wire speed of 13.5 m/min, a spot-welding time of 1.0 s and a hole with a diameter of 8.0 mm in steel plate: (a) cross section, (b) schematic of fracture location, (c) fractured interface, and (d) magnified view of region D in Fig. 13(c)

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Fig. 14

Relationship between the fracture energy and area of fractured brazed interface for CMT plug welded 1 mm thick Mg AZ31-1 mm thick galvanized steel

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Fig. 15

Fracture surface of CMT plug welded 1 mm thick galvanized steel-to-1 mm thick Mg AZ31 joint at a wire speed of 12.5 m/min, a spot-welding time of 0.6 s and a hole with a diameter of 6.0 mm in steel workpiece: (a) cross section, (b) schematic of fracture location, (c) fractured interface, and (d) magnified view of region C in (c)

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Fig. 16

Relationships between the fracture energy and fracture area for CMT plug welded 1 mm thick galvanized steel-to-1 mm thick Mg AZ31

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Fig. 17

Distortion of CMT welded: (a) CMT spot-welded (with a hole) Mg–Mg (b) CMT plug welded Mg-galvanized steel, (c) CMT plug welded galvanized steel-Mg, (d) CMT welded lapped Mg–Mg, (e) CMT welded lapped Mg-galvanized steel, and (f) effect of plug welding and material stacking sequence on weld distortion of various CMT welded Mg–Mg and Mg–steel joints

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Fig. 8

Cross section microstructure of brazing interface of (a) and (b) CMT plug welded 1 mm thick Mg AZ31-1 mm thick galvanized steel, and (c) and (d) CMT plug welded 1 mm thick galvanized steel −1 mm thick Mg AZ31

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Fig. 7

Microstructure of CMT plug welded Mg AZ31-to-galvanized steel at: (a) magnification of the middle weld metal A in Fig. 5(b) and (b) magnification of fusion zone B in Fig. 5(b)

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Fig. 4

Effect of welding variables on the strength of CMT plug welded 1 mm thick galvanized steel-to-1 mm thick Mg AZ31

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