2 Friction Stir welding and Friction Stir Department of Mechanical Processing …jaset.isnra.org/wp-content/uploads/sites/12/2019/09/... · 2019-09-07 · Friction Stir welding and

Journal of Advanced Sciences and Engineering Technologies (2019) Vol 2 No1, 40 -53

40

ISSN:2617-2070(Print);2617-2070(Online)

JournalofAdvancedSciencesandEngineeringTechnologies

availableonlineat:http://www.jaset.isnra.org

*RiyahNajimKiter1HussamJummaChalob2

1DepartmentofMechanicalEngineering,CollegeofEngineering,AnbarUniversity,[email protected]

[email protected]

Keywords:FSW,FSP,Doublepass,

Residual stress, welding aluminum alloy,optimizationFSWparameters,

Taguchi,ANOVA

A R T I C L E I N F O

Articlehistory:Received01jan2019Accepted10-Aug-2019Availableonline04-Sep2019DOI:http://dx.doi.org/10.32441/jaset.02.01.04

Copyright©2018byauthor(s)andThisworkis licensed under the CreativeCommons Attribution InternationalLicense(CCBY4.0).

http://creativecommons.org/licenses/by/4.0/

JournalofAdvancedSciencesandEngineeringTechnologiesJournalofAdvancedSciencesandEngineeringTechnologies

InvestFriction Stir welding and Friction StirProcessingfor6061-T6AluminumAlloyA B S T R A C T

6061-T6 Aluminum Alloy plates were welded by using

FrictionStirWelding(FSW)atdifferentrotationandwelding

speeds.TheeffectsoftwofactorsonUltimateTensileStrength

(UTS),whichincluderotationandweldingspeedat2otooltilt

angle,were investigated.UltimateTensile strength increases

withdecreasetheweldingspeedsandincreasestherotational

speeds.The rotation speedshave ahigher effect onultimate

tensile strength when compared with the welding speeds.

Friction Stir Processing (FSP, Double pass) led to increasing

theultimate tensilestrengthandelongationat samewelding

and rotation speeds. FSP lead to improve fatigue life and

reduceresidualstress.

©201xJASET,InternationalScholarsandResearchersAssociation

OpenAccess

Riyah N. Kiter. et al. / Journal of Advanced Sciences and Engineering Technologies

41

Introduction

Friction stir welding (FSW) considered solid-statewelding;was discovered in 1991 by TheWelding Institute [1]. In Friction stir welding,thework-pieceswere firmly clampedonto theworktable to prevent it from moving andvibration.Atthestartweldingthepinrotatesatspecified rotation speedand thenplunges intothe line interface between the two plates. Theheat generated is a product from the frictionbetweenthetoolandweldedmaterial,andtheweld material rising to a relative steady-statetemperatureandbecomesplasticized.Thetoolis moved along a predefined weld path whenplasticizedstateisreached.Thematerialintheweld zone remove from the pin entering andtravellingduring thepart try toextrudeoutofthepinholebutiskeptinplacebyshoulder[2].The generator temperature due to weldingoperationreachedto70-90%fromthemeltingpointforthebasematerialanditscausessoftenin the weld regions and permits moving thetool along the welding line. The welding toolwilltransferthematerialfromtheadvancesidetoreturnside,FSWpresentedinfigure(1)[3].Friction Stir Processing (FSP) consider as asolid – state welding process which firstlyutilized in 1999 byMishra et al [4]. FSP is anemerging surface engineering technologydependsontheprinciplesofFrictionStir

Welding. FSP worked on reduce inherentdefects in the starting material and locallyrefines microstructures and also enhance itsductility, formability, fatigue resistance,corrosion resistance, and other properties [5].Basically, FSP is a local thermo-mechanicalmetal working process, the change in theproperties occurs only in local propertieswithout affecting properties of the remainingstructure[6].ThemainadvantagesofFSWoverconventionalweldingmethodsarethedefectslikevoidsandporosity are less from conventional welding,low tensile residual stresses and distortionstresses in the resultantwelded region,highermechanical properties, the environmentallysafeprocessduetotheabsenceofradiationandtoxicfumes,FSWisoperatedinallpositions,asthere is no weld pool. Disadvantages of FSWare, the work-piece clamping is a veryimportantcriterion intheoperation, the lowerwelding speed leads to longer process times,the thickness of weld line will reduce duringthe welding process due to no filler material,when the tool is withdrawn FSW caused holeleft. When used large down forces must useheavy duty clamping to hold the platestogether,lowerflexiblethanarcandmanualProcess[7-11].


42

Figure(1,2)Frictionstirweldingandfrictionstirprocessing[12]

II-FrictionStirWeldingZones

Theweldingzonesaredividingintothreemainzonesarepresentedinfigure(3):

A. Heat affected zone (HAZ): This zone iscloser to the weld zone because of thenearness to the heat source, changes inmechanical properties due to changes inmicrostructural changes. as well as, noplasticdeformation[13].

B. Weld nugget: This zone occurs when thematerial complete undergoes

recrystallization,andproductfineequiaxedgrainstructureevolves[13].

C. Thermo-mechanically affected zone(TMAZ):Thiszonerelativetopositionsthathave undergone deformation, moreoverhavebeeninfluencedbyheat.Inthisregionno recrystallization in this region.TMAZ isplacedsoneartothepin[13].

Figure(3):WeldingzonesforFSWprocess[14]


43

III-EXPERIMENTALWORK

A. Chemicalcomposition

The material which used was aluminum alloyAA6061 with the 4 mm thickness. AluminumalloyAA6061,consideroneofthemostusedofheat treatment alloys, It has good feature as

good toughness and high strength. Thechemical composition is explained in the table(1)

B. Weldingoperation

In the current study, using 6061 aluminumalloywith 4mm thickness and length 200mmand width 100 mm. friction stir weldingparameters were (rotation speed, weldingSpeed and constant tilt angle of the too), it’sshown in table (2). A cylindrical tool made of

carbon low steel with dimension explained infigure(4).

Table(1)chemicalcompositionforstudies

material

Sample Si% Fe% Cu% Mn% Mg% Cr% Ni% Zn% Pb% Ti%

Standard[15] 0.4-0.8

0.7max

0.15-0.4

0.15max

0.8-1.2

0.04-0.35

0.25max

0.15max

0.005 0.07

Plate6061

t=4mm

0.57 0.335

0.253 0.0971

1.151 0.185 0.0034

0.0632

0.0043

0.0216

Table(2)weldingparameters

Figure(4):weldingtool.

parameter Rotation speed(rpm)

Welding speed(mm/min)



Case1 630 20 32 45

Case2 1000 20 32 45

Case3 1600 20 32 45


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C. Tensiletest

Thetensiletestwascarriedoutinuniversityoftechnology with production engineering andmetallurgydepartmentatroomtemperaturebyusing computerized (WDW-200E – 200KN) asshown in figure (4) at constant crossheadspeed 1mm/min. The tensile test specimencutting by using water jet CNC machine andperpendicular on welding line, its dimensionexplaininfigure(5).

Figure (5): Dimension of tensile test sample[16].

D. FatigueTest

Fatigue test is done at the mechanicalengineering department laboratory inNahrainUniversitybyusingfatigue(HI-TECH)-Rotatingdevice.Itisdoneataconstantstressamplitudecantilever with fully reversed (R=-1), and thespecimen dimensions were 60, 10, 4 mmlength, width, thickness respectively. Sampleswere taken from the welded plate with 1600rpmand20mm/minforbothsingleanddouble

passaswell as thebasematerial.The locationoftheweldinglineisneartothefixedpointasshowninfigure(6).

Figure(6):thepositionofweldingline.

E. HARDNESSTESTThehardnesstestwasperformedbydigitalmicro Vickers hardness TH714 shown infigure(4.18)inthemechanicalengineeringdepartmentinTikritUniversity.Thetestisdone under applied load (200 g) with atime of 15 sec. The specimenswere taken

perpendicularontheweldline.

F. X-RAYTEST

The X-Ray diffraction testswere performed intheMinistryof Science andTechnologyby the(XRD-6000/ SHIMADZU) machine type. Thesupplied current was (20 mA) and voltage(40KV).ThetargetisCopperwithawavelength(λ=1.5406A0),andthefilterisNickel.IV-RESULTS

G. Tensiletestresults

Thetensiletestresultsforbasematerialarepresentedintable(3)

Table(3):Tensiletestresultsforbasematerial.

5 6

7

Material Proofstrength0.2%(MPa)

Ultimate strength(MPa)

Modules ofelasticity

(GPa)

Elongationmax(%)

6061-T6[15] 255 289 69 12

Plate4mm 241 280 68.9 15.43


45

8 Thefigure(7)showedthatreductioninultimate tensile strength for weldmentwhencomparedwiththebasematerialforallrotationandweldingspeeds.Theweld efficiency is defined as theultimate tensile strength for weldedmaterial to theultimate tensile test forbase material. The ultimate tensilestrengthforbasematerialwas280MPawhile the higher ultimate tensilestrength for weldment was 242 MPawith weld efficiency 86.5 % at 1600rpm and welding speed 20 mm/min.The lowering tensile strengthwas 216MPa with 77.14 % at 630 rpm andwelding speed 45 mm/min. The causeof reduction tensile strength forwelding return to the different inmicrostructurebetweentheweldzonesand occurs precipitations anddissolutions in weld, while the basematerial contain same microstructure(samegrain size) [17]. From figure (8)increasing rotation speed lead toincreaseintheultimatetensilestrengthfor all welding speed. The ultimatetensile strength increase from 222.5MPa to 239 MPa and to 242 MPa atsameweldingspeed (20mm/min)andalso increase the ultimate strength inthe samepattern atwelding speed (32and45)mm/min.Thecauseofincreaseultimate strength returns to theincrease rotation speed (at samewelding speeds) lead to increase theamountofheattransferduringtheweldoperation and these heat work onincrease refines in microstructure inwelding [18]. General, the mechanicalproperties of the aluminum alloy(6061) are dependent on size anddistribution precipitations compoundsand density of compounds (needle-shaped) within the microstructure ofthesealloywhichworksonincreaseitsmechanicalproperties[18],therefore

9 the decrease in welding efficiency incase 630 rpm and 45mm/min may bedue to a random distribution of thesecomponents in this alloy. From figure(9) the ultimate strength reduces withincreasing welding speed whereby theultimate strength was 242 at 20mm/min and at increase the feed rate(welding speed) it reduces to236MPaat32mm/minafterthisitalsoreducesto 231.5 MPa at 45 mm/min. Therotationspeeds630and1000havethesame pattern when increase feed rate.The cease for reduction the ultimatetensilestrengthwhenincreasethefeedrate return to the increase feed rate(welding speed) lead to reductionmaterial flow around the welding tooland production non-homogenousdistribution for metal [19]. The figure(10) showed that relation between theelongation and feed rate (weldingspeed) for all welding and rotationspeeds and the weldment haveelongation lower than the basematerial.Theelongationreductionwithincreasing feed rate (welding speed).The cause of reduction in elongationreturn to occurrence refining for themicrostructureintheweldzoneandthegrains becomes smoother [18]. In allcases, the fracture occurs in theadvanceside.Inthesamplethatweldedby 630 rpm rotation speed and theweldingspeed,45mm/minthefractureoccursintheregionbetweentheTMEZand SZ because different in thecomposed between TMEZ and SZ. TheTMEZ composed of coarse-bentrecovered grains while the stir zonecomposed of fine recrystallized grainand this conform with T. A. Jawad [8]and H.J. Liu[19]. While the otherssample the fraction location occurs intheHAZasshowninfigure(11)duetothe significant coarsening of theprecipitated and this conforms withMishra and Z. Y.Ma[20] andG.R. Babu


46

[21]aluminiumalloyssuchasS.R.Ren et.al[22].

10 11

5 Figure(7):ultimatetensilestrength 6 7 8 9 10 11 12 13 14 15 16 17 18

Figure(8):ultimatetensilestrength-rotationspeedsFigure(9):ultimatetensilestrength-weldingspeedsforweldment.forweldment.

Figure(10):Elongation-weldingspeedsforweldmentFigure(11):fracturepositionforweldment

Rotation Speeds (rpm)

UltimateStrength(MPa)

600 900 1200 1500 1800210

220

230

240

250

20 mm/min

32 mm/min

45 mm/min

Frame 001 ⏐ 23 May 2019 ⏐ | |Frame 001 ⏐ 23 May 2019 ⏐ | |

Welding speeds (mm/min)

Elongation(mm)

20 30 40 504

4.5

5

5.5

6

630 rpm

1000 rpm

1600 rpm


Welding Speeds (mm/min)

UltimateStrength(MPa)

20 30 40 50210

220

230

240

250

630 rpm

1000 rpm

1600 rpm



47

Minitabresults

H. Optimumcase

In this work, the FSW parameters includerotationspeed(630,1000,1600)rpm,weldingspeedof(20,32,45)mm/min,andthetiltangleis constant at (2°) with the vertical axis. Thesuitableorthogonalarray(L3)waschosen.

SelectiontheL3arrayforthreeparametersandtheirthreelevelsasshowninfigure(12)inthedesignoftheexperiments(DOE)forweldedthesimilar aluminum alloys (6061-T6) to find theoptimumweldingparameter.

Figure(12):S/Nratioandultimatetom

Thefigure(13)explainstheoptimizationcaseforweldmentbydependingonS/Nratioandultimatestrengthtomean.Thebestrotationspeedwas1600rpmandbestweldingspeedwas20mm/minduetoincreasetherotationspeedanddecreasetheweldingspeedachievedgoodstirmetallicinweldingzoneandgivesbetterstrengthformaterialjoint.

Figure(13)S/Nratioandultimatetomean


48

I. ANOVAANALYSIS

By using an analysis of variance(ANOVA)thepercentagecontributionofeach factor was found. The rotationspeeds have a higher effect on tensilestrength 83.31% and the welding is

lower16.5%.

J. TENSILERESULTSFORDOUBLEPASSThe tensile test results were presentedin table (5.4). The ultimate tensilestrength foroptimumcase (singlepass)

was 242 MPa and elongation was 5.8mm, but when used FSP (double pass)theultimate tensilestrength increase to251 MPa to give weld efficiency 89%from ultimate tensile strength to basematerial while elongation increased to9.8 mm. The FSP (double pass) lead toenhance mechanical properties andmodification of microstructure. TheseresultsconformtoKadhimK.Resan,etal

[23].

K. Fatigueresults

Figure (14) explained the S-N curve for basematerial, single pass (optimum case), anddouble passes (FSP). Nine stress levels weretaken to present the S-N curve for basematerial. When a decrease in the stress levelthe number of cycles increase and reached toinfinitelife(106)whenappliedstress118MPa.Thefracturelocationinbasematerialoccursintheregionveryneartothefixedregionbecausethe stress in the region is very large whencomparedwith other regions. Figure (14) alsoexplained S-N curve single pass (optimumcase),Usually,thematerialthatweldedbyFSWhas lower ductility and strength from basematerial due to the softening in nuggets zonewhich product from the deterioration ofprecipitates. But the material that welded byFSW has better fatigue strength whencomparedwith the samematerial thatwelded

by traditional fusion welding [24]. Thereducing in fatigue strengthmaybe causedbythe grain refinement in the nugget zone, inaddition, the change inmicro-hardness duringtheweldment. Thismeans that therewill be asignificant change in the residual stresses,whichplay an important role in the life of theweldment. In FSW all of the fracture locationsoccurs in theweld zone because the region isless thickness and weaker. The FSP (doublepass) work on the higher enhancement offatigue life and mechanical properties due tothe reductionof residual stresses inweldment[25]. The fracture failure for double passlocationatlow-levelstressoccurswithoutweldzones but at high-level stress, the fractureoccursinsidetheweldzoneasshowninfigure(15).


49

Figure(14):S-Ncurveforbasematerial,singleanddoublepass.

Figure(15):fracturelocationforbasematerialanddoublepass

L. X-RAYRESULTS

From figure (16) that the residual stress forsingle pass (optimum case (single pass) ofFSW)was726MPaandithigherthanultimatetensile strength of basematerial 280MPa andthemaximumtensileresidualstressfordoublepasswas 294 and it also higher than ultimatetensilestrengthforbasematerial280MPa.But

thedoublepassledtoreduceresidualstressto59 % due to the double pass work on returndistribution residual stress in both two sidesadvancesideandreturnside.Thesereductionsexplain increase the tensile strength, hardnessandimprovefatiguelifeforadoublepass(FSP).


50

Figure(16)residualstressforasingleanddoublepass

E.HARDNESSRESULTS

The hardness for basematerialwas 99.98HV.While the minimum hardness for FSW was50HVinHAZ,andthehardnessforSZwas50.6HV and this conforms to T. Khaled [3]. Thisdifference in weld zone hardness due to theamount of heat generated which causedsoftening of HAZ, TMAZ, and NZ due todissolutionandcoarseningofthestrengtheningprecipitates during the welding operation [8].After the double pass with rotational speed(1600 rpm) and welding speed 20 mm/min.

Theminimumhardnesswasin54.5HVinHAZwith reduction of about 46.5% from the basematerial and in SZ were 79.9 HV with thereductionofabout20%fromthebasematerialas shown in figure (17). The hardnessimproved inadoublepass inSZ this return totheeffectof therecrystallizationandthemorefineness of the grains. As well as the micro-hardnessisimprovedinmostzonesthisisdueto the second pass worked on reductionresidual stresses and homogeneous it on bothsides[25].

Wave Angle (degree)

ResidualStress(MPa)

50 10050

100

150

200

250

300

350

400

450

500

550

600

650

700

750

Double Passes

Single Pass

Frame 001 ⏐ 22 May 2019 ⏐ |Frame 001 ⏐ 22 May 2019 ⏐ |


51

Figure(17):VickershardnessforBM,singlepassanddoublepass.

IV-CONCLUSION

The previous work concluded that: Theoptimumcasewasatrotationspeed1600rpmandweldingspeed20mm/mingives86.3%ofwelding efficient. Elongation and ultimatestrength increase with increasing rotationspeed and decrease welding speed. In tensilestrength,mostfailureoccursinadvancesideinHAZ,but caseone (630 rpmand45mm/min)thefractureoccursintheregionbetweenTMEZand SZ. Double pass leads to increase theultimate strength, proof strength, modules ofelasticity, hardness, elongation and reductionresidual stresses for the same welding androtationspeed.Frictionstirprocessing(doublepass)issuitabletoimprovethefatiguestrength

for element whereby the reduction in fatiguestrengthforthesinglepasswas31%whileforthe double pass was 10% only. The rotationspeed has a higher effect on ultimate tensilestrengthwas83.31%whileweldingspeedwas16.5 %. Using double pass (FSP) lead to areduction the residual stresses to 59% whencomparedwiththeoptimumcasewherebywasresidual stress in optimum case 726MPa andfor a double pass (FSP)was 294MPa at samerotation and welding speeds. The Vickershardness at the single pass in stir zone was50.6 HV0.5while at the double passwas 79.9HV0.5.


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