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Research Papers: JOINING

Cold Metal Transfer Spot Joining of AA6061-T6 to Galvanized DP590 Under Different Modes

[+] Author and Article Information
HaiYang Lei

Shanghai Key Laboratory of Digital
Manufacture for Thin-walled Structures,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China

YongBing Li

Shanghai Key Laboratory of Digital
Manufacture for Thin-Walled Structures,
State Key Laboratory of Mechanical
System and Vibration,
School of Mechanical Engineering, Shanghai
Jiao Tong University,
Shanghai 200240, China
e-mail: yongbinglee@sjtu.edu.cn

Blair E. Carlson

Manufacturing Systems Research Lab,
General Motors Research
and Development Center,
30500 Mound Road,
Warren, MI 48090

ZhongQin Lin

Shanghai Key Laboratory of Digital
Manufacture for Thin-Walled Structures,
State Key Laboratory of Mechanical
System and Vibration,
School of Mechanical Engineering, Shanghai Jiao Tong University,
Shanghai 200240, China

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received August 20, 2014; final manuscript received November 9, 2014; published online September 4, 2015. Assoc. Editor: Jingjing Li.

J. Manuf. Sci. Eng 137(5), 051028 (Sep 04, 2015) (10 pages) Paper No: MANU-14-1440; doi: 10.1115/1.4029093 History: Received August 20, 2014

In order to meet the upcoming regulations on greenhouse gas emissions, aluminum use in the automotive industry is increasing. However, this increase is now seen as part of a multimaterial strategy. Consequently, dissimilar material joints are a reality, which poses significant challenges to conventional fusion joining processes. To address this issue, cold metal transfer (CMT) spot welding process was developed in the current study to join aluminum alloy AA6061-T6 as the top sheet to hot dip galvanized (HDG) advanced high strength steel (AHSS) DP590 as the bottom sheet. Three different welding modes, i.e., direct welding (DW) mode, plug welding (PW) mode, and edge plug welding (EPW) mode were proposed and investigated. The DW mode, having no predrilled hole in the aluminum top sheet, required concentrated heat input to melt through the Al top sheet and resulted in a severe tearing fracture, shrinkage voids, and uneven intermetallic compounds (IMC) layer along the faying surface, leading to poor joint properties. Welding with the predrilled hole, PW mode, required significantly less heat input and led to greatly reduced, albeit uneven, IMC layer thickness. However, it was found that the EPW mode could homogenize the welding heat input into the hole and thus produce the most stable welding process and best joint quality. This led to joints having an excellent joint morphology characterized by the thinnest IMC layer and consequently, best mechanical performance among the three modes.

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Copyright © 2015 by ASME
Topics: Metals , Aluminum , Welding , Joining , Heat , Steel
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Figures

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Fig. 1

Schematic of welding and lap shear testing samples

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Fig. 2

CMT welding system

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Fig. 3

Illustration of the three welding modes: (a) DW mode; (b) PW mode; and (c) EPW mode

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Fig. 4

CMT plug welded 1 mm thick AA6061-T6 aluminum to 1.2 mm thick galvanized DP590 steel joints: (a) effects of welding modes and WFSs on the average joint strength (note the bars are max and min values and not standard deviation) and (b) static load versus displacement of typical joints made with three welding modes

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Fig. 5

Various fractographic images of the three welding modes at different WFS: (a) partial thickness fracture, (b) button fracture, (c) full interfacial fracture, (d) partial interface fracture, (e) SEM of position e shown in (a), and (f) SEM of position f shown in (c)

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Fig. 6

Macromorphologies of the joints on the aluminum and steel sides with three welding modes at the WFS of 5.6 m/min: (a) DW mode, (b) PW mode, and (c) EPW mode

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Fig. 7

Macromorphologies of the cross-sectioned joints with three welding modes at different WFS: (a) DW mode, 6.4 m/min, (b) DW mode, 7.2 m/min, (c) PW mode, 5.4 m/min, (d) PW mode, 6.0 m/min, (e) EPW mode, 5.6 m/min, and (f) EPW mode, 6.4 m/min

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Fig. 8

Microstructures of the IMC layer of the joints welded by CMT spot welding of 1 mm AA6061-T6 aluminum alloy and 1.2 mm HDG DP590 steel (a) SEM images of DW mode, 7.2 m/min, (b) SEM images of IMC layer of position A, (c) SEM images of PW mode, 5.4 m/min, (d) SEM images of IMC layer of position B, (e) SEM images of EPW mode, 5.6 m/min, and (f) SEM images of IMC layer of position C

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Fig. 9

Microhardness of the joints welded with three modes with unique WFS, (a) DW mode, 7.2 m/min, (b) PW mode, 5.4 m/min, and (c) EPW mode, 5.6 m/min

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Fig. 10

The shape of the welding arc of three modes at different time with the WFS of 5.6 m/min, (a) DW mode, (b) PW mode, and (c) EPW mode

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Fig. 11

Unique side view of the EPW mode welding arc with a WFS of 5.6 m/min at a time of 0.05 s after the start of welding, (a) front view and (b) side view

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Fig. 12

The metal transfer process of three modes at different time under the WFS of 5.6 m/min, (a) DW mode, (b) PW mode, and (c) EPW mode

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