gas tungsten arc welding of al-li-cu alloy 2090

8/12/2019 Gas Tungsten Arc Welding of Al-Li-Cu Alloy 2090

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Gas Tungsten Arc Welding of Al-Li-CuAlloy 2090A welding procedure for joining an Al-Li alloy is developedwhile evaluating the prope rties of various filler me tals

BY M . RA MU L U A N D M . P. RUBBERT

ABSTRACT. Aluminum-l i th ium al loys arerapidly gaining in popularity due to theirhigh strength-to-weight ratios. The developm ent o f a cost-e f fect ive metho d o fjoining these alloys is desirable for lightweight structural applications. Weldabil i tyof Al-Li-Cu Alloy 2090 is investigated usingthe gas tungsten arc (CTA) welding process. Four fil ler metals 2319, 4047, 2090and 4145 were used to we ld A l loy 2090.Mechan ica l p ropert ies o f the we ldmentswere eva lua ted and compared wi th thebase metal properties. Wit h prope r heattreatment and cleaning, weld jo int e f f i ciencies up to 65% in the as-welded c o n dit ion and up to 98% after heat treatmentwere obtained using 2319 f i l ler metal.I n t roduct ion

Aluminum-l i th ium al loys have beenkn ow n since the early 1920s, but rece ivedlittle attention in the U.S. until the 1960s.The growing interest in Al-Li alloys iscaused by their high elastic modulus andlow density compared to standard aluminum alloys. This makes them very attract ive fo r h igh-strength , low-weight app l i cations. For anAl-3Lialloy, it has beencalculated that a weigh t savings of 10% ov ero ther Al al loys can be real ized by directsubsti tut ion, and 16% by design modif ication (Ref. 1). If a commercial ly viablewelding process were available, Al-Lia l loys could be used for many otherstructural applications, such as l ightweightpressure vessels, marine hardware andlightweight armor (Refs. 1-4).Brief Survey of Welding Al-Li Alloys

Electron beam, plasma arc and laserbeam weld ing have proved to be successfu l methods fo r we ld ing Al-Li, but arel imited by low mobil i ty, h igh cost and theneed fo r a vacuum or contro l led a tmosphere (Ref. 5). Cas tungsten arc (CTA)welding is a very attractive alternativeprocess. The equipm ent has a low er cost,is more mobile and offers greater f lexibi li ty in use. The early l i terature on CTAwelding of Al-Li deals almost entire ly with

the Sovie t A l loy 01420, w i th a com position of AI-5Mg-2Li-X (Ref. 6). Alloy 01420was dev elop ed by Frid lyander in the early1960s, and has been thoroughly studied(Ref. 1). It is estim ated t o b e the m ostwidely used Al-Li a l loy in the world. Jointeff iciencies of up to 80% of base metalst rength have been repo rted w i th severa lf i l ler metals, without postweld heat treatmen t (Refs. 1, 2). W he n specimens we reresolutionized and art i f icia l ly aged, jo inte f f ic iencies o f up to 99% were reported .The main prob lem encountered whenGTA welding th is al loy was weld zoneporosi ty. I t was found tha t removing0.13 -0.40 m m (0.005-0.01 5 in.) of thesurfaceg reatly reduced or e l iminated w e ldzone porosi ty. The surface remova l wasdone by chemical mil l ing with sodium hydrox ide fo l lo we d w ith a rinse in nitric acid,or by mechanical mil l ing. A vacuum heattreatm ent at a tem pera ture of 4 50C(842F) and a vacuum of 1 0 2 to 1 0 - 5 torrwas a lso found to be e f fect ive in contro l l ing porosity (Refs. 1, 2). More recentl i terature has concentrated on Al-Li Al loy2090 (AI-2.7Cu-2.2Li-0.12Zn) and 8090(AI-2.4Li-1.4Cu-1.1Mg-0.1Zn) (Refs. 5-10,16-20). The best results published so fargive eff iciencies of 50% as welded and80 % wh en solution heat treated and aged.These are about 20% less eff icient thanSoviet we lds (Refs. 1, 2, 6, 8, 1 4-20 ). Preferred f i l ler metals include 1100, 2319,4043, 4047, 4145 and 5356 (Refs. 14, 22).A recent paper by Martukanitz examines

K E Y W O R D SAl-Li-Cu Alloy 2090CTA We ld ing2090 Base Metal2319 Filler MetalTensile StrengthRockwell HardnessWeldab i l i tyJoint EfficiencyWeld ing ProcedureHeat Treatment

the effect of f i l ler metal composit ion ontotal crack length in an inverte d T, d iscont inuous weld test. A 20-in.(508-mm) GTAweld in Al-Li 2090 plate formed cracksranging from 0.1 in. (2.5 mm ) with 4047fi ller metal to 20 .0 in. (508 mm) w ith 5356filler metal. Furthermore, the filler metals2319, 4047 and 4145 were shown to bemost compatib le with Al-Li 2090 base alloy (Ref. 20).Weld ing procedures used by d i f fe ren tinvestigators are described briefly in thereferences, and are summarized in Table

1. There does not appear to be any relat ionsh ip be tween the method o f we ld ingand the ult imate strength of the welds.Various researchers have used direct current e lectrode negative (straight polari ty)and alternating current, ut i l izing a balanced and unbalanced wave. Backingbars we re either cop per or steel, and allused a shielding gas on the back of thewe ld zo ne. The gases used are argon (Ar),hel ium (He) or an Ar-He mixture.In addit ion, some of the welds were single pass,while others used multiple passes. Theonly consistent requirement specif ied byall sources is the use of a purge gas on theroot surface. Based on this survey, i t wasfound that no procedures or guidel inesfor GTA welding of Al-Li a l loys are available in the open l i terature.

The purpose o f th is work was to exper imenta lly de termine a comple te , v iab leGTA we ld ing proce dure fo r A l -L i -Cu A l loy2090. The determinat ion o f th is p rocedure wil l a l low Al-Li 2090 to be used formany high-strength, l ightweight applicat ions that require welding during fabricat ion. The paper wil l include the preweldprepara tory procedures, we ld ing procedures, f i l ler metals and postweld treatments necessary for producing high-eff iciency welds. Properties and performanceof weldments are evaluated by tensi lehardness testing and by optical examinat ion o f the we ldment microstructure .

M.RAMULUan dM. P. RUBBERT arewith theDepartment of MechanicalEngineering University of Washington. Seattle, Wash.

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Table 1A Summary of Al-Li Alloy WeldingAuthor(Ref. no.)

Pickens (1)Pickens (2)

Kou (6)Kruger (8)

Skillinberg (16)

Martukani tz* 3 ' (18)

Alloy0142001420

01420D T D

809020902090

FillerMetals0142001420

01420xxxAS-AIMg4.5M8090209041454047

ProceduresW e l dEff iciency80%80%

80%

4 5 - 4 6 %

4 0 - 5 0 %

Other DataUses argon arc GTAWwith 190 AUses 15 V, 90-105 A,75 deg . V-g roove , 75% He-

25 % Ar gas mixtureUsed asymmetr ical pulsedw a v e f o r mUsed Ar gas, steel backing bar,no purge, 175 A. Welds werevery porous.Used Ar gas, 60 deg. V-groove,2 passes, 70% straight-30%reverse unbalanced wave, 190 A.U se d G M AW , 6 7 % H e -

33 % Ar gas, 240 A, 32 V.(a) Q uo te d in Ref. 18.

Table2ChemicalComposition in wt-% and Mechanical Properties of AI-Li-2090AlloyLi

1.763Cu

2.70Zn

0.10Zr

0.08Mn

0.05Fe

0.12Si

0.10Ti

0 .10Cr

0.05Na

0.002K

0.003Al

balanceN o t e : Yield Strength: 538 MPa (78 ksi)

Ult imate Tensi le Strength: 585 MPa (84.9 ksi)Elongation: 7

Modulus of Elast ic i ty: 11.5 X 10 6

shiny finish using a bearing scraper andwiped wi th acetone. This removed anypossible surface contaminat ion that mighthave occurred af ter mil l ing.All Al-Li 2090 filler metal has the samepropensi ty as the p late towards contamination. I t was not pract ical to mechanically clean the filler metal rods, so theywere chemically cleaned immediatelypr ior to welding. The cleaning treatmentconsisted of f irst chemically milling the rodfor 10 minutes in 30% sodium hydroxideat 131F(55 C).The f i l ler metal was thenrinsed in water, cleaned in 30% nitric acidand rinsed in water. After this, it was driedat203F (95C) for one hour to removeall water. All other f iller metals were freshand br ight as received . Since they do notcontain Li, there are no problem s wi thformat ion of a hydrogen-enr iched layeron the surface to pro mo te poro sity. Thesef i l ler metals were wiped with acetone anda whi te cot ton c loth unt i l c lean, but noother special preparat ion was done. Furthermore, al l f i l ler metals were handledonly whi le wear ing c lean whi te cot tongloves af ter they were prepared for w e l d ing, to prevent possible contaminat ion byskin oils, water, or other contaminantsfrom the hands.

Exper imenta l Setup andW e l d i n g P r o c e d u r e sMaterials

Al-Li Alloy 2090-T8E41 rolled plate in athickness of 0.250 in. (6.35 mm) was usedfor the evaluat ion. Composi t ion and mechanical propert ies are shown in Table 2.Four filler metals used in this study were2319, 4047, 4145 and 2090. All f iller metals, except the 2090, are commerciallyavailable in 0.125-in. (3.2-mm) diameterrod form. The 2090 f i l ler metal was obtained by shearing 0.125-in. (3.2-mm)sheet into 0.1 25-in. (3.2-mm) square strips.Table 3 shows the nominal chemical composition of the filler metals.Specimen and Preweld Preparation

A good preweld preparat ion procedu re , usually cleaning, is crit ical for suc-

0.012 in. 0.3 mm )

cessful GTA welding of aluminum in allcases (Refs. 21 , 22). To avo id contamina t ion or porosity problems, a str ict mult i-step preparat ion procedure was used before all welding trials. Each plate wassheared to 6 X 12 in. (152 X 304 mm),represent ing one half of each weldingsample. The roll ing direct ion was parallelto the 6-in. (152-mm) side. Welds weremade perpendicular to the roll ing direct ion ;therefore, a12-in.(304-mm) side wasdry milled at a 60-deg angle to the flat.Wh en tw o p lates we re but ted together , a60-deg single-V was formed. In addi t ion,plate surface was dry m il led to a dep th of0.012 in. (0.3 mm) for a distance of 0.5 in.(12mm) f rom the edge of the V, as show nin Fig. 1. This was p erfo rme d to preventpossible weld joint contaminat ion by surface hydrogen enrichment of the alloy.Immediately pr ior to welding, the ent iremil led area was scraped to a smooth,

0.25 in. 635 m m)

Welding SetupWeld ing was done manual ly on a P&HDA3 00 HFGW weld ing machine. The cur rent sett ing was medium, with a range of60-195 A ut i l iz ing alternate current. Oneplate was welded at the Boeing Companyusing a Mil ler Synchrowave 300 squarewave machine. The gauges on the Mil lermachine indicated 110 A at 30 V whileweld ing . Both machines used a 0.125-in.(3.2-mm) zirconiated tungsten electrodeand 50ft3 /h(23.6 L/h) of 75% He-25% A rshieldinggas.The backs of the welds we repurged with 100% Ar gas.All welds were made using a steelbacking bar with a 1-in. (25.4-mm)wi de X 0.500-in. (12.7-mm) dee p gaschannel. The Al-Li plates were sealed tothe backing bar with aluminum tape. Thisprov ided a good purge whi le prevent ingcontact and possible contaminat ion be

tween the weld and the bar. To minimizeplate shif t ing and warpage, the plateswere clamped to the backing bar withsteel strongbacks. Run-on and run-off tabswe re w eld ed across the ends of the jointsto help restrain the plates.All welds w ere made using four passes.

Table3Nominal Composition in wt-% ofthe Aluminum Filler Materials[20]

0.5in .(12 mm)Fig.1W eld joint configuration.

Al loy2090231940474145

Si0.1-12.010.0

C u2.76.3-4.0

M g--

Li1.76--

Zr0.1--

Albalbalbalbal

110-slM A R C H 1 9 90


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The first three passes were on the front ofthe plates, fi l ling the V-g roo ve. Th e plateswere a l lowed to coo l be low110F (43C)be twe en passes to minimize theeffectso fthe heat input necessary for we lding. Thewe ld zon e was stainless steel wi re brushedand wiped with acetone after each pass.The brushing removed the surface con taminants f rom the previous pass. Afterthe third pass, the back of the weld jointwas go uge d ou t using a 0.375-in. (9.5-mm)ball end-mil l . The gouge w as cleaned by astainless steel wire brushing and an acetone w ipe , then weld ed w ith a single pass.All welds were made perpendicular to theroll ing direct ion. Extreme care was takento avoid contaminat ion of the welds. Thetungsten e lect rode was reground beforestarting eachw e l d ,and not contam inatedby touching the weld whi le weld ing . Cleanwhite cot ton g loves we re also wo rn w hen ever cleaned f i l ler metal was handled , andthe scraped area of the plates was nottouched after cleaning.Postweld Treatment

Some of the specimens were postw eldheat t reated. The heat t reatment wasper formed to improve weld s t rength byprecipitat ion strengthening the fusion andheat-af fected zone (HAZ) and to reduceresidual weld stresses. The procedureconsisted of a solut ion heat t reatmen t forone h our at 950F (510C), and cold wa ter quenching, fol lowed by art if ic ial agingat 329F (165C) for 18 h.Test ing

The f inished welds were tested usingthe tension test and Rockwell hardnesstest. They were also examined using opt ical microscopy. Specimens were prepared by cutt ing each 12-in. (304-mm)wid e w eld ed plate into f ive 2- in. (50.8-mm) wi de samples, af ter t r imm ing 1 in.(25.4 mm) from each end of the weld toeliminate edge effects. These sampleswere bandsawed to the approx imateshape for standard tensile specim ens, thenmilled to final dimensions. The wel d beadreinforcement was also removed, and thetensile cross-section machined to a unifor m thickness, as sho wn in Fig. 2.All tension tests were made on a TiniusOlsen 60,000Ib (27,300 kg) capacity tension testing machin e. The strain rate for alltests was 0.025 in. (0.635 mm ) per m inute .All deformat ion took place in the weldarea, so the standard 2% offset rule foryielding is not valid with a 2-in. gaugelength.Instead, several tests we re run foreach trial to f ind the breaking point for thewelds, and the apparent yield point , andstrain behaviorof the metal was noted byobservat ion of the load indicator. Afterthese trials, the extensometer was used toconf irm the observed yield point of theweld of one or two tests in each trial.Theextensometer was remo ved af ter y ie ld ing

i

12 in. 304 mm]

r

J

. . .

f

2 in 50 mm )

0 5in . 12mm)

Fig. 2Tension test specimen.and before fracture to avoid possibledamage. Pieces cut from the samples during the shaping of the tensile specimenswere used to make Rockwell hardnessand opt ical microscopy specimens. O p t i cal microscopy specimens were polishedto 0.1-micron f inish and etched withKeller 's solut ion. The Rockwell hardnesswas tested on the polished specimens after they were photographed and examined.All hardness tests we re don e using aWilson Rockwell hardness tester, Model

400

cocoLUcc\co

300

200

100

Ranges from 0.15 in. 3.8 mm). to 0.20 in. 5.1 mm ). Eachspecimen was m illed so thatthe cross section was flat anduniform, then measured to0.001 in. 0.025 mm ).

0.25 in . 6.35mm)

4)R. Hardness was tested in the we ld ,across the HAZ, and in the base metal.Results and Discussion

Typica l stress-strain curves of as-w elde dand a heat t reated and aged we ld , using2319 and 20 90 f i ller metals, are sho wn inFig. 3. The results of the tension tests using 2319, 4047, 2090 and 4145 filler metals are sho wn in Table 4, and the joint eff iciency of the weldments is shown in Fig.Fig. 3-Typicalstress straindatafrom weldtensionspecimens.

FILLER MATLS.-Q- 2319AW-- 2090AW- - 2090HT-o - 2319HT

0.000 0.004 0.008 0.012STRAIN (mm/mm)

0 016 0 . 0 2 0

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As-Welded---AWH e a t T r e a t e d 8 Aqed---HT&A

5

Fig. 4Weld jointefficiency.AW HT&A AW HTSA AW HTSA AW HTSA2319 4047 2090 4145

FILLER MATERIALS

Fig. 5A Typicalfracture surface ofas received basemetal.Al Li2090;Bheattreated andaged.

.1

7 .

. 6Fracturedtensile specimen showingvisible necking before fracture. A - Weld w ith2319filler me tal and testedas-welded;Bweld with 20 90 filler metal and testedas-welded.

4.The eff iciency is calculated from the ult imate tensile strength of the weld me nt incomparison to the base metal ult imatetensile strength. The results presented areaverage values obtained from test ing twoor three specimens of each trial. Therefo re , it should be cautioned that theresults shown are not statistically val id,and should be considered preliminary until verif ied. The base metal ult imate tensilestrengths (UTS) averaged 60.3 ksi (415.8MPa) as rec eive d, and 65.6 ksi (452.3 MPa)after heat treatment. Figure 5 shows thebase metal tensile fracture surfaces exhibit ing ductile fracture, but no significantnecking. The UTS of the base material inthe as-received con dit ion was l isted as 78ksi (537.8 MPa), after machining the specimens, this value was found to be60.3 2.9 ksi (537 20 MPa) in ten tensile tests. This reduction in UTS is attributed to the effect of the as-milled surfacefinish of the test specimens. Since all ten sile specimens we re prepa red in the sameway, this reduct ion in strength should notaf fect the comparisons that are made onthe basis of joint efficiencies.

The 2090 and2319filler metals gave thebest results, wi th bo th prov iding ov er 60%of base metal UTS in the as-welded con d i t ion . Figures 6 and 7 show the typicalfracture specimens and fracture surfaces.All welds made with these filler metalsbroke through the weld itself . The weldswith these filler metals also showed con siderable duct i l i ty in the as-welde d co ndit ion . The large amount of plastic strainbefore fracture is shown by a visiblenecking of the specimensFig. 6. Therewas alsosignificant plastic strain observedafter the yield point was reached (and theextensometer removed). The fracture surfaces of these specimens(Fig.7) show thetradit ional cup-and-cone and angledshearing. After heat t reatment, the 2319filler metal gave 98 .6% of base m etal UTS,while the 2090 f i l ler metal gave 87.9%.The heat t reated welds lost much o f theirduct i l i ty. There was no necking, and thespecimens fractured soon after the yieldpoint was reached.The 4047 and 4145 filler metals gaveultimate stren gths of less than 60 % of base

metal UTS, both before and af ter heattreatment. Welds from these f i l ler metalsbro ke at the edge of the w e l d . These fillermetals were found to have very l i t t leplastic strain after the yield point and before fracture. There was no visible necking obse rved. The 4145 f i l ler metal sho wsa cup-and-cone duct i le f racture of thejoint . However, the joints with 4047 f i l lermetal appear to be in the duct i le-br it t lefracture transit ion zone. In an ef fort to reduce the heat input to theweldzone, onetrial was run using 2319 filler metal and a90-deg single-V groove. The increase inthe joint angle requires less penetrationf rom the torch to the bot tom of the jo int ,so less heat is required. This trial gave an

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a s - w e l d e d s t r e n g t h o f 3 9 . 6 ksi ( 2 7 3 M Pa ) ,o r 65 .7% o f ba se met a l UTS. Th is i s a 5%i m p r o v e m e n t o v e r t h e 6 0 - d e g j o in t c o n f i g u r a t i o n .

A n i n t e r e s ti n g a n d i m p o r t a n t o b s e r v a t i o n w a s m a d e w h i l e h e a t t r e a t i n g t h e2 0 9 0 w e l d s . O n e s p e c i m e n w a s a g e d f o ro n l y 1 2 h in s t e a d o f 1 8 , a n d t h e U T S w a s3 6 . 6 ks i o r 2 5 2 . 3 M P a ( 6 1 % b ase UTS) . Th isi s e sse n t i a ll y i d e n t i ca l t o t h e a s - w e l d e dspe c im ens . It is poss ib le t ha t t he 2 09 0 ,4 0 4 7 a n d 4 1 4 5 f i l l e r m e t a l s co u l d a l l b e n e f i t f r o m i n c r e a se d a g i n g t i m e . T h i s n e e d sf u r t h e r i n ve s t i g a t i o n .

O p t i ca l M i c r o sco p yO p t i c a l m i c r o s c o p y s h o w s f o u r d i s t in c t

z o n e s i n e a c h w e l d : b a se m e t a l ( BM ) ,h e a t - a f f e c t e d z o n e ( H A Z ) , r e s o l i d i f i c a ti o nzo n e ( R Z ) o r t h e p a r t i a l ly m e l t e d r e g i o n ,a n d w e l d b e a d ( W B ) . T h e R Z - W B , H A Z - R Za n d B M - H A Z i n t e r fa c e s in a w e l d w i t h2 3 1 9 f il le r m e t a l a r e sh o w n i n F ig . 8 . T h e r eis a co u r se n e d d e n d r i t i c g r a i n s t r u c t u r e i nt h e W B z o n e a n d a n a r r o w b a n d s h o w i n ga g l o b u l a r g r a i n s t r u c t u r e p r e se n t a t t h eW B - R Z b o u n d a r y . G r a i n s i z e is q u i t e v a r i ab le i n t hese a rea s, an d is m uc h la rger t ha nt h e o r i g i n a l BM g r a i n s . T h e sa m e o b se r va t i o n s w e r e f o u n d t o b e t r u e f o r a l l f i l l e rm e t a l s , b o t h a s - w e l d e d a n d a f t e r h e a tt r e a t i n g a n d a g i n g .

T h e r e a r e a l a r g e n u m b e r o f p r e c i p i -

Table 4Tension Test ResultsFillerMetal

Base MetalPWSH A(lj)2319PW SH &A4047PW SH &A2090PW SH &A4145PW SH &A(a) Al l strengths in

Tria l NumberNumber-99101014111212

MPA(b) Pos twe ld so lu t ion hea t t rea ted and aged(c) Yield strength cou ld no t be ascer ta ined .

Tests3232S23232

YieldStrength

358.5386.1179.2351.6none (c)n o n e 'c '144.8379.2none (c>n o n e 'c '

UTS'High455.0460.6259.9448.2233.7215.1254.4408.8244.8274.4

)Low

393.0444.0241.3444173.1177.2249.6386.1228.2267.5

Avg.415.8452.3251.0446.0211.6198.6251.0397.8234.2271.0

Fig.7-Fractured surfaces of the as-welded specime ns. Awith 2090 filler metal. Weld with 2 319 filler metal; B-weld

H I

R e s o l i d i f i c a t i o n Zone Weld

* * .

BMFig. 8 Typical metallurgicalchanges observed in a weld with2319 filler metal A - Weld beadresolidification zone; B basemetal HAZ interface;Cresolidification zone-HA Zinterface.

HAZ

jilftsSH

*HAZ R e s o l i d i f i c a t i o n 7nne

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Fig. 9Hardness vs.distance from theweld.

FILLER MATLSO 2319AW

2319HT

2090AW

2090HT

4047AW

4047HT

4145AW

4145HT

10 15 2 0DISTANCE mm)

t a tes v i s ib le i n t he BM, seen as b lack do tsin t he f i gu res . They a re a l so seen in t heW B , R Z a n d H A Z a s d a r k l in e s a r o u n d t h eg r a i n b o u n d a r i e s , as w e l l i so l a t e d i n c l u s i o n s . A f t e r h e a t t r e a t m e n t a n d a g i n g ,m a n y o f t h e p r e c i p i t a t e s w e r e f o u n d t oh a v e b e e n d i s s o l v e d . T h e g r a i n b o u n d ar ies a re s t il l v i s ib le , bu t t h ey a re m uc hf a i n t e r , a n d t h e s i ze a n d n u m b e r o f i n c l u s i on s h a v e b e e n r e d u c e d . T h e f e w p o r e sp r e s e n t s h o w t h a t t h e p r e w e l d c l e a n i n ga n d w e l d i n g p r o c e d u r e s h a v e a v o i d e d t h ep r o b l e m o f w i d e s p r e a d p o r o s i ty r e p o r t e din t he l i t e ra tu re . The 2319 t r i a l w i t h t he9 0 - d e g j o i n t s h a p e a l s o s h o w e d a g r e a t l yr e d u c e d H A Z i n c o m p a r i s o n t o t h e 6 0 - d e gj o i n t . T h i s co r r e l a t e s w i t h t h e i n c r e a se dt e n s i l e s t r e n g t h o f t h e 9 0 - d e g j o i n t .

Rockwe l l HardnessA l l w e l d s s h o w e d s o f t e n in g t h r o u g h o u t

t h e w e l d a n d H A Z i n t h e a s - w e l d e d c o n d i t i o n , b u t t h e 4 0 4 7 a n d 4 1 4 5 f i l l e r m e t a l ssh o w e d a so f t e r zo n e i n t h e b a se m e t a l a tt h e e d g e o f t h e w e l d ( r e so l i d i f i ca t i o nz o n e ) , c o m p a r e d t o t h e 2 3 1 9 a n d 2 0 9 0f i l l e r meta l s . The f i l l e r meta l s t hemse lvesw e r e a ll v e r y s o f t i n t h e a s - w e l d e d c o n d i t i o n . A g r e a t e r d i f f e r e n ce is se e n a f t e r h e a tt r e a t i n g . T h e b a s e m e t a l i n a l l t h e w e l d sr e t u r n e d t o t h e o r i g i n a l h a r d n e ss , b u t t h ef il le r m e t a l s sh o w e d a l a r g e va r i a t i o n i nh a r d n e ss . T h e t yp i ca l p l o t o f R o ck w e l lh a r d n e ss vs . d i s t a n ce f r o m t h e w e l d f o r23 19 f i l le r me ta l is s h ow n in F ig . 9 . Th e2 0 9 0 a n d 2 3 1 9 f i l l e r m e t a l s b e ca m e a sh a r d a s t h e b a se m e t a l a f t e r h e a t t r e a t m e n t . W h i l e t h e 4 1 4 5 f i l l e r m e t a l h a r d e n e d c o n s i d e r a b l y , t h e 4 0 4 7 g o t s o f t e ra f t e r h e a t t r e a t m e n t . T h e so f t e n i n g o f t h e4 0 4 7 f i l l e r m e t a l p r o v i d e s a d d i t i o n a l e v i d e n c e t h a t a n o t h e r h e a t t r e a t m e n t c o u l db e m o r e e f f e c t i v e t h a n t h e o n e n o w b e

i n g u se d . It is r e a so n a b l e t o a ssu m e t h a t ad i f f e r e n t h e a t t r e a t i n g p r o c e d u r e c o u l d b eo p t i m i ze d f o r e a ch f i l l e r m e t a l . T h i s i s a na r e a f o r f u t u r e r e se a r ch .C o n c l u s i o n s

It h a s b e e n e xp e r i m e n t a l l y sh o w n t h a tA l - L i - C u 2 0 9 0 ca n b e su cce ss f u l l y G T Aw e l d e d . W e l d s a r e m a d e u s i n g 7 5 % H e ,2 5 % A r sh i e l d i n g g a s , a n d a 6 0 - d e g s i n g l e -V g r o o v e w e l d . A p r e w e l d c l e a n i n g t r e a t m e n t co n s i s t i n g o f m e ch a n i ca l m i l l i n g ,s c r a p i n g a n d a n a c e t o n e w i p e w a s f o u n dt o p r o d u c e s o u n d w e l d s . T h e w e l d s w e r em a d e u s i n g m u l t i p l e p a sse s , w i t h c o o l i n ga n d c l e a n i n g b e t w e e n p a s se s . A s o l u t i o nh e a t t r e a t m e n t a n d a r t i f i c i a l a g i n g a f t e rw e l d i n g p r o d u c e t h e s t r o n g e s t w e l d s ,j o i n t e f f i c i e n c i e s u p t o 6 5 % o f b a se m e t a ls t r e n g t h a r e p o ss i b l e i n t h e a s - w e l d e dc o n d i t i o n . A f t e r h e a t t r e a t m e n t , j o i n t e f f i c i e n c i e s o ve r 9 8 % a r e o b t a i n a b l e . T h i sw o r k s h o w e d t h e b e s t r e s u lt s a r e o b t a i n e d u s i n g 2 3 1 9 f i l l e r m e t a l .

AcknowledgmentsT h e a u t h o r s a r e g r a t e f u l t o D r . G . W .

O y l e r f o r hi s i n sp i r a t i o n a n d e n c o u r a g e m e n t a n d f o r t h e s u p p o r t o f t h e W e l d i n gR e se a r ch C o u n c i l . T h e h e l p f u l a d v i ce a n dm a t e r i a l s su p p l i e d b y E . C o s t e l l o , C . G r i f -f e e o f t h e B o e i n g C o m p a n y a n d R. M a r t u ka n i t z o f A l co a a r e s i n ce r e l y a p p r e c i a t e d .

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gas tungsten arc welding of al-li-cu alloy 2090

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