CMT焊接翻译3

JOM,Vol.66,No.6,2014

DOI:10.1007/s11837-014-0970-7

Ó

2014TheMinerals,Metals&MaterialsSociety

Al-Si-MnAlloyCoatingonAluminumSubstrateUsingCold

MetalTransfer(CMT)WeldingTechnique

,

1

J,

1

1,2

1.—DepartmentofMetallurgicalandMaterialsEngineering,IndianInstituteofTechnology

Madras,Chennai600036,India.2.—e-mail:sbakshi@

Thecoldmetaltransfer(CMT)processwasexploredasaweldoverlaytech-

niqueforsynthesizingAl-Si-MnalloycoatingonacommerciallypureAlplate.

Theeffectofweldingspeedonthebeadgeometry,depositionrate,andthe

dilutionwerestudiedandthebestparameterwasusedtosynthesizethe

processcanbeusedtoproducethickcoatings(>2.5mm)

kershardnessnumberof

suggestedthattheCMTprocesscanbeaneffectiveandenergy-efficient

techniquefordepositingthickcoatingsandisusefulinweldrepairofalumi-

numalloycomponents.

INTRODUCTION

Aluminumanditsalloysarewidelyusedfor

automotivecomponentsduetotheirlowdensity,

adequatestrength,andhighspecifi

theysufferfrompoorwearresistance,whichcould

leadtoshorterlifeofthecomponentsduetodamage.

Surfacecoatingscanbeveryusefulinimprovingthe

erlayscanbeusedfor

applyingcoatingsaswellasforrepairingdamaged

lsprayprocessessuchascold

spraying,

1

plasmaspraying,andhigh-velocityoxy-

fuel(HVOF)spraying

2

havebeenusedfordepositing

lspray

ofaluminumcompositesalsohasbeenreportedfor

lsprayoffersthe

advantageoffinegrainsizeandevennanocrystalline

depositshavebeenreported.

3

However,thelimita-

tionofthermalspraycoatingisthatitproduces

usuallya50-to100-lmcoatinginasinglepassand,

hence,isnotrecommendedforhigherthicknesses.

Suchalowdepositionrateisnotgoodforrepair

applicationsinwhichalargecrackorwornoutsur-

esionstrengthof

thecoatingisalsoreducedifadequatesurfaceprep-

imitationsareovercomein

erlay(orweld

cladding)isawell-knowntechniqueofcoatinga

tings

canbeappliedforimprovingthecorrosionresistance,

wearresistance,orboth.

4

Gas-metalarcwelding

(PublishedonlineApril30,2014)

(GMAW),

5

gastungstenarcwelding(GTAW),

6

and

plasma-transferredarc(PTA)

7

arefewexamplesof

fusionweldingprocessesthatareusedforweld

heimportantfeaturesin

weldcladdingisthedilutionofthecompositionofthe

n-

ventionalGMAWprocessisusedforweldoverlayof

aluminum,theheatinputisveryhigh,leadingto

highdilutionlevels.

5

Asaresultofhighthermaland

electricalconductivityandacomparativelylow

meltingpoint,itisdifficulttocoataluminumusing

nwelding

processwithlowheatinputandhighefficiencyis

desiredtosolvethisproblem.

Coldmetaltransfer(CMT)isamodifiedGMAW

processinventedbyFroniusInternational(Petten-

bach,Austria).TheCMTprocessbasicallyoperates

intheshort-circuit(diptransfer)modecharacter-

,lowheat

ortantmodificationofCMTover

conventionalGMAWisthefulldigitalcontrolofthe

efeedintheCMTprocess

iscontrolledbyamicrocontrollerthroughfeed

motorsandisnolongerdependentontheelectrical

ialhighpulseofcurrentis

supplied,forminganarcbetweentheadvancing

electrodewireandthesubstrate,whichmeltsthe

rentisreducedfollowingthe

pulse,andassoonastheshort-circuitformationis

indicatedbyasharpdecreaseinvoltage,thecurrent

isreducedtoafurtherlowbackgroundvalueand

1061

1062

thewireisretracted,leadingtothedetachmentof

,inthisprocess,themetal

transfertakesplacewhenthecurrentisverylow

,ithasbeen

nciplesoftheCMTprocess,

equipment,operationdetails,advantages,applica-

tions,andlimitsarewellstudiedandreported.

8

Somereportsontheweldingofaluminumalloys

usingtheCMTprocesshaveshownthatthisprocess

isgoodforthinsheetsowingtothelowheatinputin

tinputalsoresultsinreduced

spatter

andgapbridgingabilitywhilejoining

–10

thinsections

oftheprocesswerealsoreported.

8

Thisprocess

hasthebenefitofprovidingonlytheenergyneeded

fortheprocess,

CMTprocesshasalsobeenusedindissimilarmetal

joiningapplicationssuchasaluminumalloytogal-

vanizedsteels,wherejoiningoccursbybrazingof

aluminumontosteel.

8,11,12

CMThasalsobeen

reportedforjoiningofaluminumandmagnesium

usingcopper-based(CuSi

14

3

),

13

aswellas4047alu-

minumalloyfillerwires.

Thus,theCMTprocessis

recommendedforautomotivejoiningapplications

CMTprocessisalsostudiedforthejoiningoftita-

niumalloystoaluminumalloysaswellascopper

alloys,andtheimportanceofprocessinaerospace

andmedicalapplicationswasreported.

15,16

Onlyafewreportsareavailableintheliterature

thathaveusedtheCMTprocessasasurfacecoating

in

andRutili

17

reportedthattheCMTprocesscouldbe

suitablyusedforanticorrosivecoatingapplications.

Inthisstudy,afeasibilitystudyfortheCMTprocess

asacoatingmethodfordepositingInconel625alloy

onthesurfaceofcarbon-manganesesteelsheetwas

processwascomparedwith

theconventionalpulsed-arcmodeandtheCMT-

pulsehybridmodewithrespecttodilutionand

oundthatamongthethree

modes,pureCMTshowedthelower

18

dilutionand

etal.

studiedthe

CMTprocessforalow-dilutioncladdingapplication.

ItwasobservedthattheCMTshort-circuitmode

waspresentonlyinthelowerparameterrange,and

therewasatransitiontoacombinationofshort-

circuitplusspraymodeoftransferinthemiddleto

ploredtheCMT

processforlow-dilutioncladdinginaternaryalu-

minumalloy(Al-Cu-Mg)withabinaryfillerwire

Al-2319(Al-Cu).TheAl-Cu-Mgalloyisknowntobe

susceptibletoahot-crackingproblemwhenwelded

withbinaryaluminumalloyfi

processwasusedforcladdingtheternaryalloywith

thebinaryalloy,whichwasthenweldedwithcon-

ventionaltechniques,thusreducingthechancesof

ly,OlaandDoern

19

studied

CMTascladdingprocessforanickel-basedsuper

portedthedevelopmentofdefect-free,

perfectlybondedcladsandrecommendedthe

Rajeev,Kamaraj,andBakshi

processforrepairofnickel-basedsuperalloyparts

ingasturbines.

Thereisnoreportsofaronaluminumcoatings

ectiveofthecurrentworkisto

examinetheCMTprocessasaweldoverlaytech-

effectsofweldingprocessparametersondilution

andbeadangle,whichareimportantforproducing

asoundoverlaycoating,

hardnessvariationofthesubstrateaftercoating

wasalsostudied.

EXPERIMENTALPROCEDURE

WeldCladdingbyCMT

Thesubstratewasapure-Al(99%)plate3mm

thick,andthecoatingwasmadefromanAl-Si-Mn

fipositionof

thefifaceofthe

Alplatewascleanedwithastainlesssteelwire

brushtoremoveoxidelayersandothercontami-

nants,anditwassubsequentlycleanedwithace-

ansplusSynergic

4000fromFroniusInternationalwasusedforthe

tage,cur-

rentandfeedratewerevariedoverarangeofval-

isiblydefect-freeweldbeadwas

obtainedforaparticularsetofparameters,the

asusedasthe

shieldinggaswithaconstantflowrateof15L/min.

TableIIshowstheparametersforthethreebeads

gwaspreparedbylaying

weldbeadssidebysidewiththebestparameters.

Sufficienttimewasgivenbetweensuccessivewelds

toavoidapreheatingeffect.

CharacterizationoftheBeadsandCoating

Thecrosssectionofthebeadwasgroundand

polished,andopticalmicroscopywascarriedout.

Opticalmicroscopyofthebeadswascarriedout

usingastereomicroscope(.,

Chennai,India).Beforeobservationinthemicro-

scope,thebeadsweremacroetchedusingDix-Keller

ngelectronmicroscopy(SEM)ima-

gesofthepolishedcrosssectionofbeadandcoating

wascarriedoutusingaQuanta200SEM(FEI

Company,Hillsboro,OR)equippedwithanenergy

dispersivex-rayanalysis(EDAX)facility(EDAX

itionofthematerialsused

AlbaseplateAl-Si-Mnfillerwire

Elementwt.%Elementwt.%

Al99Al94.3

Si0.64Si3.47

Fe0.25Mn1.88

Cu0.075Fe0.3

Ti0.02Ti0.05

Al-Si-MnAlloyCoatingonAluminumSubstrateUsingColdMetalTransfer(CMT)WeldingTechnique1063

Inc.,Mahwah,NJ).Thehardnessofthecoatingwas

measuredusingaVickersmicrohardnesstester

(WolpertWilson,Aachen,Germany).

RESULTSANDDISCUSSION

OptimizationofParameters

Figure1ashowsthetrialscarriedouttoobtain

eparameterssuch

ascurrentandfeedratewereset,threebeads

werepreparedatdifferentweldingspeedsof

6.4mm/s,8.5mm/s,and10.6mm/s(corresponding

to15in./min,20in./min,and25in./min,respec-

tively).ThethreebeadsareshowninFig.1aonthe

2showsthepictureofthepol-

firstthingto

noteisthattheareaofcrosssectionofthebeadand,

hence,thevolumeofthebeadperunitlength

r

quantitythatisveryimportantistheheatinputper

unitlength,andthisquantityalsoreduceswith

antityiscalcu-

latedbydividingtheelectricalpowerinputbythe

weldingspeed,andafactorisintroducedtotake

tersusedforwelding

Parameters

Voltage(volts,V)

Current(ampere,A)

Wirefeedrate(m/min,F)

Nozzle-to-platedistance(mm,N)

Weldingspeed(in./min,S)

BeadA

12.5

80

4.8

5

15

BeadB

12.5

80

4.8

5

20

BeadC

12.5

80

4.8

5

25

Fig.1.(a)Pictureshowingthebeadtrailsandthebeadsforgoodparametersatdifferentweldingspeeds.(b)Coatingpreparedbydepositing

overlappingbeadswithparametersobtainedfromtrials.

microscopeimagesofthecrosssectionof(a)beadA,(b)beadB,and(c)beadC.

1064Rajeev,Kamaraj,andBakshi

careoftheconversioneffiviousthat

thehigherisheatinputperunitlength,thehigher

thedilutionwillbe.

Thedilutioncanbecalculatedfromthepercent-

ageofthetotalcross-sectionalareaofthebead,

whichliesbelowthesurfaceofthesubstrateas

herway,dilutioncanbe

obtainedforeachofthemajorelementsinfillerwire

andisobtainedbythefollowingformula:

Dilutionð%Þ¼

M

C

M

Coating

ÀC

Filler

C

M

Filler

Â100(1)

ticshowinghowdilutionwascalculatedandthebead

angledefinition.

thevariationofthepercentdilutionandbeadangle

withweldingspeed.

whereC

M

isthecompositionofmetalM(M=Al,Si,

andMn).

Dilutionmaynotbeveryimportantcriteriainthe

followingstudy,butitisnecessarytoknowhow

angleswerecalculatedasshowninFig.3,andan

4

showsthevariationofthebeadcontactangle,the

dilution,andthedepositionrateasafunctionof

weldingspeed,

observedthatastheweldingspeedincreases,the

dilutionisdesiredbecause

seenthatasthespeedisincreasedfrom15in./minto

20in./min,thedilutiondrasticallyreducesfrom23%

to8.3%.Thedepositionrateisreducedonlymar-

ginallyfrom6cm

3

/minto5.7cm

3

/d

angle,however,increasesfrom67°to89°.Butasthe

speedisincreasedto25in./min,thedilutionisde-

creasesonlymarginallyto7.7%,butthebeadcontact

anglebecomes101°.Also,thedepositionrate

reducesdrasticallyto4.3cm

3

/,itisob-

servedthatthebeadangle,dilution,andthedepo-

sitionratevarynonlinearlywiththeweldingspeed.

Abeadangleoflessthan90°isdesirablesothat

thereisnolackoffusiondevelopedwhenthecoating

,

theweldingspeedof20in./minisfoundtobethe

suitableforoverlaycoatingsinthiscase.

Figure5showsthevariationofthecomposition

compositionswereobtainedbyanenergydispersive

x-rayspectroscopy(EDS)analysisofsmallareaat

differentdistancesalongthelineshowninthefig-

enthatthepercentageofAldecreases

observedthatthevariationofSiandMnismoreor

lesssimilarinbeadsAandB,whileinbeadCthere

ruptchangeisduetothe

r,theparameter

Cisnotsuitableforthedepositionofcoatingsdueto

onwascalculatedbased

ontheaveragecompositionofaluminuminthebead.

Thevalueofdilutionofaluminuminthecoatingis

lesscomparedtothatobtainedfromareacalcula-

duetothefactthatboththesubstrate

andcoatingarerichinaluminum.

Figure6showsthehardnesstakenalongthe

en

in

accordancewiththelowerdilutionandincreasein

tiesoftheweldbeads

Property

Beadcontactangle(°)

Depositionrate(cm

3

/min)

Dilutionbasedonarea(%)

DilutionbasedoncompositionofAl(%)

BeadA

101

6

23

2.8

BeadB

89

5.7

8.3

2.6

BeadC

67

4.3

7.7

1.1

Al-Si-MnAlloyCoatingonAluminumSubstrateUsingColdMetalTransfer(CMT)WeldingTechnique1065

gesofthepolishedbeadsalongwiththecompositionalongthelineforbeadA(a,d),beadB(b,e),andbeadC(c,f).

ionofhardnessalongthedepthofthebeads.

r,

beadCisnotsuitableformakingcoatingsduetoan

improperbeadangle.

CharacterizationofCoatings

Basedontheresultsofthebeads,thewelding

parameterforbeadBwasselectedasthebest

gwas

preparedbyoverlayingseveralbeadssidebyside.

Figure1bshowspicturesofthecoatingmadeby

isseenthatmostofthesurfacelooksdefectfree.

isseenthatthecoatingsshowsthedistinctfeature

ofaweldoverlaycoatingwhereindividualbeads

erfaceis

foundtobeverygoodwithoutanycracksoroxides.

Thelackofasharpinterfacesuggeststhatthereis

metallurgicalbondformationbetweenthecoating

andsubstrate,whichiscausedbythepartialmelt-

unlikethesharpdis-

cernibleinterfaceinthermalspraycoatingswhere

cansaythatthebondstrengthwouldbegoodinthis

reafewpores,whichmayduetothe

factthatthebeadangleis89°,whichiscloseto90°.

Itistobenotedthatthethicknessofthecoatingin

singlepassismorethan2.5mmandsuchthick

coatingsareveryhelpfulinweldrepairapplica-

hickcoatingwiththermalspray

techniquewouldrequirebetween25and50passes.

Thus,CMThasadistinctadvantagehereinterms

oftheenergyinputandthetimerequiredforcar-

ryingoutanyrepairoperations.

Figure8showsthevariationofcompositionalong

sobtainedbycar-

ryingoutanEDSanalysisonasmallareaatdif-

ferentdepthsonthepolishedcrosssectionofthe

rageAlpercentageinthecoating

wasfoundtobe95.1%,whichgivesadilutionof

0.9%.Similarly,thedilutionofSiandMnwasalso

calculatedandfoundtobe27.3%and28.6%,

hvalueofSiandMnisbecause

averylow

levelofdilutionandisconsistentwithreportson

mple,LorenzinandRutili

17

calculatedthedilutionbyanalyzingthecomposition

1066Rajeev,Kamaraj,andBakshi

tructureoftheweldcladshowinggoodinterfacewithsomeporosity.

Fig.8.(a)SEMimageofthepolishedcrosssectionand(b)com-

positionalongtheline.

ofironalongthedepthofInconelcoatingdeposited

onC-Mnsteelandhaveobservedverylowdilution

withCMTcomparedtoconventionalthepulsemode

,OlaandDoern

19

measuredthe

dilutionofInconelweldoverlaybytheareamethod

andreportedalowvalueofdilutionproducedbythe

howingvariationofthehardnessalong(a)depthand

(b)widthofthecoating.

Al-Si-MnAlloyCoatingonAluminumSubstrateUsingColdMetalTransfer(CMT)WeldingTechnique1067

oneadvantageoftheCMT

tion,the

lowpowerinputmakesitapromisingtechniquefor

industrialapplication.

HardnessoftheCoatings

Figure9ashowsthevariationofthemicrohard-

nessofthecoatingwiththedepthfromthesub-

stratetothecoating,whereasFig.9bshowsthe

variationofthehardnessalongthewidthofthe

rdnesstestswerecarriedoutonthe

served

fromtheplotsthattheVickershardnessnumber

(VHN)increasedfrom28inthebulkto57inthe

coating,andthereisadiscontinuousjumpaswe

findingisin

accordancetotheincreaseintheSiandMnasseen

eethatCMTcanbeaverygood

techniqueforlarge-scaledepositionofcoatingsand

canbeeasilyusedforweldrepair.

CONCLUSION

Thefollowingconclusionsaredrawnfromthe

currentwork:

processcanbeusedtodepositalumi-

numalloyweldcladswithlowdilutionlevels.

dangle,depositionrateanddilutionare

nonlinearfunctionsoftheweldingspeed.

gformsverygoodmetallurgicalbonding

withthesubstrateduetopartialmeltingofthe

substrate.

gwiththicknessgreaterthan2.5mmcan

beproducedinasinglepass,whichisconsider-

ablyhighcomparedtothermalsprayprocesses.

processisfoundtobealow-energy

processforweldrepairofAl-alloycomponents.

ACKNOWLEDGEMENTS

jacknowledgesfundingfromthe

NavalResearchBoardofIndiaforestablishingthe

CMTfacility.

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