Mechanical Properties of Gas Metal Arc and Friction - DiVA Portal

123 Pages·2013·28.67 MB·English

by  Christina Rødsand Breivik

Mechanical Properties of Gas Metal Arc
and Friction Stir AA6082-T6 Weldments
Christina Rødsand Breivik
Materials Technology
Submission date: June 2013
Supervisor: Trond Furu, IMTE
Co-supervisor: Øystein Grong, IMT
Norwegian University of Science and Technology
Department of Materials Science and Engineering

Preface
The present report is part of an international collaboration project between Norway and
Qatar,wheretheinvolvedcompanieshavebeenHydroAluminium,QatarPetroleumand
Qatalum.
ThetriptoQatarinthebeginningoftheprojectwasveryinformativeandofgreatinspira-
tionandmotivationforthefurtherwork.
SupervisorsandcontactsduringtheworkhavebeenprofessorØysteinGrong1andTrond
Furu2. IwouldliketogiveaspecialthankstoprofessorØysteinGrongforhisthorough
and constructive guidance. In addition, I would like to thank all the other individuals
assistingmeduringtheproject.
Trondheim,June2013
ChristinaBreivik
1NorwegianUniversityofScienceandTechnology(NTNU),Trondheim
2HydroAluminium,Sunndalsøra
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Abstract
The general purpose of the presents report is to determine the mechanical properties
of AA6082-T6 subsequent to gas metal arc welding (GMAW) and friction stir welding
(FSW).Hardnesstestinghasbeencarriedoutfortheweldments. Inaddition,tensileand
CharpyV-notchtestinghasbeencarriedoutfortheunaffectedbasemetal,thefusion/stir
zoneandfortheheat-affectedzone(HAZ),bothtransverseandlongitudinaltotheweld-
ing/extrusiondirection.
ItisconcludedthatHAZsofteningisamajorproblembothintheGMAandtheFSweld-
ments. Still,thetotalwidthoftheHAZintheFSweldmentsissmallercomparedtothat
observed in the GMA weldments. The total strength reduction for the GMA and the FS
welds was 43 and 34%, respectively. The general observations is that the FS weldments
showslightlybettermechanicalpropertiescomparedtotheGMAweldments. Thisisfur-
ther reflected in the calculations of load-bearing capacity of the joints, showing that the
FSweldmentsexhibitthehighestcapacityunderotherwiseidenticalconditionsduetothe
combinedeffectofalowerHAZstrengthreductionandasmallerHAZwidth.
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Sammendrag
Detgenerelleforma˚letmeddennerapportenera˚ bestemmedemekaniskeegenskapenetil
AA6082-T6pa˚følgendeavgassveising(GMAW)ogfriksjonssveising(FSW).Detharblitt
foretatthardhetsma˚lingerlangsdenvarmepa˚virkedesonen(HAZ).Itilleggharstrekk-og
ska˚rslagstesingblittgjennomførtfordetupa˚virkedegrunnmaterialet,forsmelte/røresone,
og for HAZ. Prøvene har blitt tatt ut enten pa˚ tvers eller pa˚ langs av ektruderingsretnin-
gen.
Det har blitt konkludert med at HAZ mykning er et stor problem ba˚de ved GMAW og
ved FSW. Likevel blir den totale bredden av HAZ mye smalere ved FSW sammenlignet
medGMAW.DentotalestyrkereduksjonenvedGMAWogFSWvarhenholdsvispa˚43og
34%. GenereltviserFS-sveisenebedremekaniskeegenskapersammenlignetmedGMA-
sveisene. Dettestøttesavberegningenegjortforlastbærenedekapasitetavsveisene,som
viser at FS-sveisene har større kapasitet sammenlignet med GMA-sveisene under like
forhold. Dette kan forklares med den kombinerte effekten av lavere HAZ styrkereduk-
sjonogsmalerebreddepa˚ HAZ.
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Contents
Preface i
Abstract iii
Sammendrag v
Contents viii
1 Introduction 1
2 Theory 3
2.1 PhysicalmetallurgyofAl-Mg-Sialloys . . . . . . . . . . . . . . . . . . 3
2.1.1 Processroute . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1.2 Grainstructureandtexture . . . . . . . . . . . . . . . . . . . . . 5
2.1.3 Precipitationhardening . . . . . . . . . . . . . . . . . . . . . . . 6
2.1.4 Fracturemechanisms/mechanicalproperties . . . . . . . . . . . . 7
2.2 GasMetalArcWeldingofAl-Mg-Sialloys . . . . . . . . . . . . . . . . 8
2.2.1 TheGMAWprocess . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.2 Thefusionzone . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.3 Theheat-affectedzone . . . . . . . . . . . . . . . . . . . . . . . 12
2.3 FrictionStirWeldingofAl-Mg-Sialloys . . . . . . . . . . . . . . . . . . 14
2.3.1 TheFSWprocess . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.3.2 Nugget/stirzone(SZ). . . . . . . . . . . . . . . . . . . . . . . . 15
2.3.3 Thermo-mechanicallyaffectedzone . . . . . . . . . . . . . . . . 16
2.3.4 TheFSWheat-affectedzone . . . . . . . . . . . . . . . . . . . . 16
2.3.5 Mechanicalpropertiesoffrictionstirwelds . . . . . . . . . . . . 17
2.4 Load-bearingcapacityofweldedcomponents . . . . . . . . . . . . . . . 18
3 Experimental 21
3.1 Basematerial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1.1 Chemicalcomposition . . . . . . . . . . . . . . . . . . . . . . . 21
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3.1.2 Castingandhomogenizationconditions . . . . . . . . . . . . . . 21
3.1.3 Extrusionandheat-treatment . . . . . . . . . . . . . . . . . . . . 22
3.2 Weldingofthesheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.2.1 Gasmetalarcwelding . . . . . . . . . . . . . . . . . . . . . . . 22
3.2.2 Frictionstirwelding . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3 Samplepreparationandmetallographicexamination. . . . . . . . . . . . 23
3.3.1 Opticalmicroscopy . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3.2 Hardnesstesting . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.4 Tensiletesting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.5 Impacttesting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.6 FracturesurfaceanalysisintheScanningElectronMicroscope(SEM) . . 29
4 Results 31
4.1 OpticalmicrographsofGMAandFSwelds . . . . . . . . . . . . . . . . 31
4.2 HardnessprofilesofGMAandFSwelds . . . . . . . . . . . . . . . . . . 33
4.3 Tensiletestresults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.1 GMAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.3.2 FSW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.4 Fractographyofthetensilespecimens . . . . . . . . . . . . . . . . . . . 45
4.4.1 GMAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.4.2 FSW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.5 CharpyV-notchtestresults . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.5.1 GMAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.5.2 FSW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
5 Discussion 63
5.1 ComparisonofmechanicalpropertiesbetweentheGMAandtheFSweld-
ments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.2 Hardnessprofilesandyieldstress . . . . . . . . . . . . . . . . . . . . . . 69
5.2.1 Comparisonofthehardnessprofiles . . . . . . . . . . . . . . . . 69
5.2.2 Relationshipbetweenhardnessprofilesandyieldstress . . . . . . 72
5.3 Load-bearingcapacityofGMAandFSwelds . . . . . . . . . . . . . . . 74
5.3.1 Loadingperpendiculartoweld . . . . . . . . . . . . . . . . . . . 74
5.3.2 Loadingparalleltoweld . . . . . . . . . . . . . . . . . . . . . . 75
6 Conclusion 79
7 Bibliography 81
Appendix 85
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