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Thearccharacteristicsandmetaltransferbehaviourofcoldmetaltransferanditsuseinjoiningaluminiumtozinc-coatedsteelARTICLEinMATERIALSSCIENCEANDENGINEERINGAJANUARY2009ImpactFactor:2.41DOI:10.1016/j.msea.2007.11.124

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HongtaoZhangHarbinInstituteofTechnologyatWeihai15PUBLICATIONS148CITATIONS

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Availablefrom:HongtaoZhangRetrievedon:08August2015

Materials Science and Engineering A 499 (2009) 111113

Contents lists available at ScienceDirect

Materials Science and Engineering A

journa l homepage: www.e lsev ier .co

The arc vioand its d s

H.T. Zhan Wana School of Mat 9, Shab State Key Lab rbin 1Heilongjiang Pr

a r t i c l

Article history:Received 23 MReceived in reAccepted 19 N

Keywords:CMTArc characterisMetal transferDissimilar met

ed mheatdiede resCMT

1. Introduction

In ordeto make caparts to suing aluminresolved. Jby fusion wof the formdeteriorateand Sepoldif the commechanicaexistence oto steel.

Fusionwdissimilarma fusion wmay give aShort-circulow heat inthe weldinrecent devfer (CMT) p

CorrespoE-mail ad

dissimilar joint owing to the no-spatter welding process and low

0921-5093/$doi:10.1016/j.r to reduce pollution and save energy, it is attractiver bodies lighter through introducing some aluminiumbstitute for the previous steel structures [15]. So join-ium to steel becomes a key problem which should beoining dissimilar metals such as aluminium and steelelding methods is known to be very difcult becauseation of brittle intermetallic compounds which canthe mechanical properties of the joints. But Kreimeyer[6] have shown that, when joining aluminium to steel

pound layer is less than 10m thick, the joint will belly sound. Furthermore, the author also deems that thef zinc coating can increase the fusion metal wettability

eldingmethods become the hot direction to solve theetal joiningproblembecauseof their high efciency. So

elding method with low heat input and high efciencysolution to realize the aluminium use in automobile.iting metal transfer is a suitable method because of itsput characteristics [7]. But the excessive spatter duringg process also poses great problems to the producer. Aelopment in welding technology is the cold metal trans-rocesswhich is ideally suited towelding aluminiumand

nding author.dress: hitzht@yahoo.com.cn (H.T. Zhang).

thermal input.The CMT process is a modied metal inert gas welding process

which was invented by Fronius company. The principal innovationis that the motions of the wire have been integrated into the weld-ing process and into the overall control of the process. The wireretraction motion assists droplet detachment during the short cir-cuit, thus the metal can transfer into the welding pool without theaid of the electromagnetic force. Then the heat input and spattercan be decreased greatly.

The major aim of this article is to examine the arc character-istics and the metal transfer of the CMT process and use it tojoin aluminium and zinc-coated steel with a lap geometry by aweldingbrazing method. The microstructure of the joint and thetensile strength of the joint were investigated to evaluate the pro-cess applicability in dissimilar metal joining.

2. Experimental set-up and procedure

A high-speed camera (CA-D6-0256W) was used to acquire theimages of the arc shapes and the droplet images. When collectingthemetal transfer process a back light is projected by the left xenonlamp to travel towards the droplet/wire and then the image planeas a set of parallel lights. The lter system was used to diminishthe intensity of the light and promote the image articulation. Thecurrent and voltagewaveformwere captured by the correspondingsensors and then written into the computer.

see front matter 2008 Elsevier B.V. All rights reserved.msea.2007.11.124characteristics and metal transfer behause in joining aluminium to zinc-coate

ga,, J.C. Fengb, P. Heb, B.B. Zhangb, J.M. Chenb, L.erials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai 26420oratory of Advanced Welding Production Technology, Harbin Institute of Technology, Haovince, PR China

e i n f o

ay 2007vised form 30 October 2007ovember 2007

tics

al joint

a b s t r a c t

Cold metal transfer (CMT) is a moditransfer process, characterised by lowdroplet transfer process have been stujoin aluminium to zinc-coated steel. Ththe welding process can be realized byobtained by the CMT process.m/locate /msea

ur of cold metal transferteel

gb

ndong Province , PR China50001,

etal inert gas welding process based on short-circuiting theinput and no-spatter welding. The arc characteristics and itsby high-speed video photography. The process was used toults shows that no-spatter welding and low heat input during, and a dissimilar metal joint with good performance can be

2008 Elsevier B.V. All rights reserved.

112 H.T. Zhang et al. / Materials Science and Engineering A 499 (2009) 111113

Fig. 1. The arc shape variation of the CMT process during one cycle (one frame per ms, view . . . mm across).

Fig.

Deep draof 0.6mm a1mmwerediameterwwas adoptesurface of t

3. Results

3.1. The arc

The arc sone cycle, tbeginning owaveform f

A typicaFig. 2. A cydroplet of mwe can divphase. This

a hign ofo forigh.d by2. The current and voltage waveforms of the CMT process.

wing sheets of hot dip galvanized steel with thicknessnd sheets of pure aluminium 1060 with thickness ofused inwelding experiments. AlSi alloywire in 1.2mmere selected as thellermetal. Inweldingprocess, argond as shielding gas at a ow rate of 15dm3/min. The

ing toignitiotrode tvery hresentehe samples was cleaned by acetone before welding.

and discussion

characteristics and metal transfer of the CMT process

hape variation of the CMT process as shown in Fig. 1. Inhe brightness of the arc is low except two frames at thef the cycle. These characteristics are consistentwith theeatures of the process.l CMT welding electrical signal cycle is shown incle can be dened as the period required to deposit aolten electrode into the weld pool. From the gure,

ide the cycle into three phases: (i) the peak currentis represented by a constant arc voltage correspond-

a little liquinhibit theThis phaserent keeps(iii) The shwith the warc extingutor to urgepool.

Fig. 3 is tsize of thethe wire dialiquid bridgforce the drof the elect

Fig. 3. The metal transfer process during CMT process (one framFig. 4. Cross-sectional optical image of the joints.

h pulse of current. The high pulse current make thethe welding arc easily and then heats the wire elec-m droplet. In this phase, the brightness of the arc is(ii) The background current phase. The phase is rep-

a lower current. Through the peak current phase,

id droplet is formed on the wire tip. In order toglobular transfer, so the current decreases abruptly.is the background current phase. Then the low cur-constant until the short-circuiting process happens.ort-circuiting phase. In this phase, the wire contactseld pool and the arc voltage changes into zero and theishes. The back-drawing force becomes the main fac-the droplet break away from the wire into the weld

he metal transfer process in one waveform period. Theliquid droplet attaching to the wire tip is very close tometer during arc-burning time. And the rupture of thee is very stable. Because of the additional back-drawingoplet can transfer into thewelding pool without the aidromagnetic force.

e per ms, view . . . mm across).

H.T. Zhang et al. / Materials Science and Engineering A 499 (2009) 111113 113

Fig. 5. Microstning electron m

Fig. 6. X-

3.2. The mialuminium/

The smowelding bacFig. 4 is theelectron milayer betwewelding pro

The joinsteel. X-raytion of thecompact laylike compou

The maaluminium

ig. 7. T

hat tthatt-aff

clus

ed onructures of interface between steel andweldmetal, obtained by scan-icroscopy.

F

show t86% ofthe hea

4. Con

Basray diffraction pattern of the fracture plane near the weld metal.

crostructure and tensile performance of thezinc-coated steel joint made by CMT

othwelding seamwasmade and the zinc coating of thek seamcanbe retained to keep the corrosion resistance.typical cross-section image of the joints. The scanningcrograph shows that a visible intermetallic compounden the steel andweldmetal has been formed during thecess as shown in Fig. 5.t was disjoined at the interface betweenweldmetal anddiffraction was used to determine the phase composi-compound layer. The results are shown in Fig. 6. Theer near the steel side is Fe2Al5 phase and the needle-nd growing into the weld metal is FeAl3 phase.ximum thickness of the compound layer in thesteel interface is about 4m. The tensile test results

were drawn

The metalheating befeatures anDissimilarwithout crcompoundmain consiThe thickntrolled undtensile stre

Acknowled

The reselent Talents

References

[1] E. Schuber115 (2001)

[2] E. Schuber[3] K. Haraga,[4] J.K. Larsson[5] W.S. Miller[6] M. Kreime[7] M.J.M. Herhe fracture location of the joint (designated by white arrow).

he bonding strength is about 83MPa,equaled almost toof the pure aluminium and the fracture all occurred inected zone of the aluminium as shown in Fig. 7.

ions

the experimental results and discussions, conclusionsas follows:

transfer process of the CMT is very stable and the archaviour is changed based on the special wave controld a assistant back-drawing force.metal joining of aluminium to zinc-coated steel sheetacking by the CMT process in a lap joint is possible. Thelayer at the interface between steel and weld metalsts of Fe2Al5 and FeAl3 phase.ess of the intermetallic compound layer can be con-er 5m, so the joint strength can be guaranteed. Thength can arrive at 83MPa.

gement

arch is sponsoredby theProgramforNewCenturyExcel-in University.t, M. Klassen, I. Zerner, C. Walz, G. Sepold, J. Mater. Process. Technol.28.t, I. Zernet, G. Sepold, Proc. SPIE 3097 (1997) 212220.Weld. World 44 (2000) 2327., Weld. Res. Abroad 49 (2003) 2945., L. Zhuang, Mater. Sci. Eng. A 280 (2000) 3749.yer, G. Sepold, Proceedings of ICALEO02, Jacksonville, USA, 2002.mans, Weld. J. 78 (1999) 141173.