a new low-melting-point aluminum braze

7/27/2019 A New Low-Melting-Point Aluminum Braze

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A N e w L o w - M e l t i n g - P o i n t A l u m i n u m B r a z e

A n e w f il le r m e t a l fo r b r a z i n g p r e v i o u s l y " u n b r a z e a b l e "a l u m i n u m a l lo y s i s e v a l u a te d

B Y D . M . J A C O B S O N , G . H U M P S T O N , A N D S . P. S . S A N G H A

ABSTRACT. Most h igh-st rength a lu-m in u m e n g in e e r i n g a l l o y s c a n n o t b ejo ined by braz ing because they e i ther de-grade or me lt at the temperature at wh ichcon in ie rc ia l l y ava i lab le a lum inum brazesare used . Previous efforts to de velo p alu-minu m brazing f i l ler metal a l loys with as igni f icant ly reduced melt ing point havetended to be frustrated by poor mechani-cal propert ies of the alloys, corrosion oft he jo in t s o r t he h igh cos t , t ox ic i t y o rvo lat i l i ty of the const ituent mater ials. Thispaper descr ibes the developnlent and as-sessment of a new brazing a l lo y wi th acomposi t ion of 73AI -20Cu-2Ni-5Si (wt -%) , which has been designed to over -come these l imitat ions.A join ing process has been devised forf lux less braz ing of a luminum engineer-ing a l loys us ing the new f i l ler metal foruse in both iner t gas and vacuum fur -naces. The product ion of duct i le fo i l pre-fo rms and ro l l - c lad base meta ls is de-scr ibed together w i th pre l im inary resultsof mech anical proper ty assessments andcorros ion resistance tr ials. The se resultsa re h igh ly encourag ing and po in t t op r o m is in g n e w a p p l i c a t i o n s f o r a l u -n l inu m brazing technology.I n t r o d u c t i o n

The use o f severa l impor tan t a lu -min um engineer ing a l loys is constra inedbecause their melt ing points are belowthose of the ava i lable braz ing f i l ler m et -a ls . They are "unbrazeable" by ex is t ingtechnology. The se inc lude al loys in the2xxx and 7xx x ser ies (Ref . 1). The a l ter -D . M . JA C O B S O N , G . H U M P S T O N a n d S. PS . S A N G H A a r e w i t h H i r s t D i v i s i o n , G E C -M a r c o n i M a t e r i a l s L td ., B o r e h a m w o o d , U . K .

nat ive jo in ing methods o f mechan ica lfastening and adhesive bonding imposesevere constraints on com pon ent geom -et ry , and esp ecia l ly on the m inim um sec-t ion th ickness. The mechanical in tegr i tyof adhes ively bonded jo ints can be var i -able and they have a poor resistance topeel failure. Moreover, th ey cannot toler-ate extended exposure to elevated tem-perature, wh i le their e lect r ica l and ther -m a l c o n d u c t i v i t i e s a r e c o n s id e r a b l yinfer io r to those of the base metals. Weld -ing o f a lun l inun l a l loys is w ide ly p rac -t iced , bu t i t can compromise the me-chan ica l p roper t ies , espec ia l ly inwrought and prec ip i tat ion-st rengthenedalloys , due to the degradat ion producedin the heat-affected zone (HAZ). Solder-ing, whi le technical ly achievable, is in-capab le o f f u rn ish ing jo in t s w i t h ade-quate strength and corrosion resistancefo r many eng ineer ing app l ica t ions : t hestrength of soldered joints can be of theorder of one f i f th that of brazed jo ints(Ref. 2). Thus, there is a clear need for

K EY W O R D SAluminum Braz ingBrazing Fi l ler MetalLow M el t ing Po in tAl lo y Select ionDuct i le Foil PreformFluxless JoiningQuaternary AI A l loyAI Engineer ing Al loyMechanical Proper t iesCorrosion Resistance

new a lum inum-based b raz ing f i l le r met-a ls and the deve lopm ent of a f i l ler metalusable at about 500C (930F) could en-able up to 90% of all structural and cast-ing grades of a luminum to be jo ined bybrazing.The lowes t me l t ing po in t a lum inumbrazes cur ren t ly ava i lable are based ona lu m in u m - c o p p e r - s i l i c o n f o r m u la t i o n sand are only pract ica bly usable down toabout 590C (1090F). For the -90 % ofalum inum al loys that can be brazed, theprox im i t y o f even th is t empera tu re t othe i r me l t ing po in t demands s t r ingen ttempera tu re con t ro l dur ing the jo in ingoperat ion. This is d i f f icu l t to achiev e onlarge assemblies, due to the inadvertentdeve lopment o f t empera tu re g rad ien tsand temperature var ia t ions from item toi tem in h igh-volume batches. For manyof the h igh-st rength a lum inum engineer-ing ma ter ials a temperature o f 590C isunacceptably h igh because ei ther theyrnelt or their mechanical propert ies arec o m p r o m is e d . F o r p r e c ip i t a t i o n -strengthened a lloys, the joinin g tempera-ture should coinc ide with that at whichthe solut ion- t reatment is car r ied out, typ-ica l ly in t he reg ion o f 480 t o 540C(895 to 1000F) , wi th the prec ip i tat ionaging being car r ied out at a lower tem-perature in a subsequent step.Bes ide the requ i rement f o r b raz ingf i l ler metals sui table for a lumin um al loysthat have a reduced melt ing p oint , thereis a m ore general n eed for f i l ler m etalsthat can be used in the temperature rangeo f a b o u t 3 0 0 - 5 5 0 C ( 5 7 5 - 1 0 2 5 F ) .The av ai lable range is severely l imi ted tomateria ls that are e i ther in t r ins ical ly ex-pensive because they conta in a large pro-por t ion of gold, or they are br i t t le andcannot b e produced in the form of foil

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Table 1 - - Binary Eutectic Alloys with Aluminum (Ref . 12)Element Entering nto EutecticEutectic with Alum inum Eutectic Com position Temperature

silver AI-7t .9wt-%Ag 567C (1053F)copper AI-32.7wt-%Cu 548C (1018F)germanium AI-51.6wt-%Ge 420C (788F)magnesium AI-35.6wt-%M g a/ 450c(a) (842 F)silicon AI-12.6wt-%Si 577C (1071 F)zinc AI-94.0wt-%Zn 381 C (718F)(a) There are three eutectics in the aluminum-magnesium system, but the high volatilit y of magnesium means that only thealuminum -rich eutectic m erits consideration as a brazing fille r metal.and w ire preforms. The f i rs t type of a l lo yis represented by the 96.8Au-3.2Si and87.SAu-12 .5Ge (wt -%) eu tec t ic a l loys ,melt ing at 363C and 361C, respec-t ive ly , whi le the second type is typi f iedby the 16.5Ag-63AI-20.5Ge alloy, with ame lt ing poin t of 414.5C (Ref. 3). Wo rk-able a luminum al loy f i l ler metals of re-duced melt ing po int migh t a lso be capa-ble of sat isfy ing th is w ider requirement .Prev ious a t t empts t o deve lop low-mel t ing-po in t f i l le r meta ls f o r b raz ingalum inum al loys have not met wi th co m-merc ia l success due to one o r moredrawbacks. These inc lude poor mechan-ical propert ies of the alloys, suscept ibil-i ty of the jo ints to corros ion, vol at i l i t y ofthe const ituents or high cost of the con-s t i t uen t meta ls o r t he fabr ica t ion o fbrazements.O b j e c t i v e s

To have opt im um ut i l i t y , an a luminu mbrazing a l lo y should satis fy the fo l lo win gset of co ndi t ions:1 A braz ing temperature in the regionof 500C and a nar row melt ing range, i . e .the a l loy should be of eutect ic or near eu-t e c t i c c o m p o s i t i o n . A n a r r o w m e l t i n grange is one prerequis i te for a f i l le r metalt o exh ib i t h igh f lu id i t y dur ing b raz ing(Ref. 4).b) High f lu id i ty when molten. Brazedalum inum assemblies intended for engi-neer ing app l ica t ions shou ld possessst rong jo ints , w hich in turn mea ns thatthey should be nar row and be wel l f i l le d(Ref . 5) . Again, a eutect ic a l loy wouldbest meet this requirement.3 ) The ab i l i t y t o be used wi thou tf luxes in a protect ive gas atmosphere.Inert gas f low furnaces ne ed not be so-ph is t ica ted o r expens ive , as we havefound. F luxes fo r a lum inum and the i rresidues are high ly corros ive and specialmeasures need to be taken dur ing theiruse and also subsequent ly to ensure theirtota l remova l fo l low ing braz ing (Ref . 6) .The n eed for post-process cleanin g to re-mov e cor ros ive res idues can m ore thanoffset the ad dit ion al costs of inert gas fur-nac ing , es pec ia l ly f o r sma l l hea t ex -

changers and other assemblies of corn-plex geom etry, representat ive o f the elec-tronics and aerospace industr ies. Thereare exceptions to this and a f lux for braz-i n g a lu m in u m w i t h c o n v e n t i o n a l a l u -min um -si l icon f i l le r metal a l loys in a ir isa v a i l a b le c o m m e r c ia l l y , wh i c h i sc la ime d to be "non corros ive " (Ref . 7) .4 ) M e t a l l u r g i c a l c o m p a t i b i l i t y w i t haluminum engineering mater ials, part icu-lar ly for jo in ing th in-w al led sections, i . e .brazing, should resul t in minimal sub-strate erosion and no em brit t l in g phasesshould be formed as a result of wett ingand a l loy ing w ith the base mater ia ls.5) Electrochemical com pat ib i l i t y wi ththe base metals. Ga lvanic co r ros ion canbe a major source of weakness in jointsmade in a lum inum and i ts a l loys. To min -imize th is problem the e lect rode poten-t ia ls of the b ase mater ia ls and the brazemust be c lose ly matched.6) Low cost. The const ituent metalsshould be inexpensive.7 ) The a l loy shou ld be capab le o fbeing processed into braz ing a l loy pre-forms, in par t icu lar fo i ls . This require-ment is norm al ly cont ingent on the a l loyhaving suf f ic ient duct i l i t y to enab le i t tobe mechan ica l ly worked to a range o fpreform geometr ies, inc luding fo i l andcladdings.A l l o y S e l e c t i o n

The pr imary const i tuent of any newb r a z in g f i l l e r m e t a l s u i t a b le f o r a l u -m inum a l loys has to be a lum inum be-cause th is prov ides the best chance ofa c h ie v in g m e t a l l u r g i c a l a n d e le c t r o -c h e m ic a l c o m p a t i b i l i t y w i t h a l u m in u mengineer ing materia ls . Al lo y ing a ddi t ionsare needed to depress the l iqu idus tem-perature be low that of a lum inum (661 C;1222F).Brazes tha t a re ava i la b le comm er -c ia l l y f o r jo in ing a lum inum are based ona lum inum -s i l icon , w h ich has a eu tect icpoint o f 577C (Refs. 8-10 ) . The pres-ence of the s i l icon does not marke dly af -fect the corrosion character ist ics of alu-min um (Ref. 11 ) . Fur therm ore,hypoeutec t ic a l loys ( con ta in ing


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Aluminum Z incThe eutect ic point in the a luminum-zinc system is almost three hundred de-grees belo w that of a lum inum , but at theexpense of an overwhelming propor t ionof z inc, whic h is even more vola t i le thanmagnesium at a g iven temperature. H ow -ever, zin c v apo r is less react ive than mag-

nesium and coats exposed sur faces,whereas magnesium vap or cor ros ively at-tacks many m ater ials. The rela t ive ly smalldif ference in the electrode potent ials o fa lum inum and z inc m in im izes the sus-cep t ib i l i ty of jo in ts made wi th a lum inum -zinc a l loys to galvanic cor ros ion. Zinc isless reactive to oxygen than alum inum sothat provided the furnace atmosphere issuf f ic ient ly iner t to permit the jo in ing ofa luminum components, the z inc wi l l notox id iz e. For these reasons, z inc- r ich a lu-min um -zinc a l loys are used as solders fora lum inum (Refs. 17, 18) .

A l u m i n u m - r i c h b i n a r y a l u m i n u m -zinc a l loys with a l iquidus in the regionof 500C (930F) are not suitable for useas brazes on account of their wide melt -ing range (appro x im ate ly 70C, o r]25F) , wh ich impa i r s t he i r sp read ingcharacteristics. F urthermo re, the servicetemperature of assemblies wo uld be l im-i ted to app roxim ately 400C (750F) bythe re la t ive ly low so l idus tempera tu re .This par t icu lar problem can be overcom eby coat ing the a luminu m components tobe jo ined w ith a layer of z inc just a fewmicrons th ick . B ecause the layer of z incis very thin, it is possible to dif fuse thismetal com plete ly in to the base mater ia lat the braz ing temperature with in a fewhours. This technique , kno wn as d i f fu-sion-brazing, has been successfully usedfo r jo in ing a lum inum- l i t h ium eng ineer -ing mater ia ls . Wi th an 8090 t ype a lu -m in u m - l i t h i u m b a s e m a t e r i a l , t h e a s -bonded strength of simple lap-shear testp ieces was repor ted as averaging 120MPa (17.5 x 10 s ps i ; Ref . 19) , whi chcompares favorably wi th the values ob-ta ined us ing a convent ional a luminum-si l icon eutect ic braze. The appl icabi l i tyo f t h is approach is l im i ted by the ex -tended heat ing cyc le t imes and by theneed to apply some pressure to force theabutt ing surfaces into int imate contact.The second of these requirements stemsf r o m t h e s m a l l v o lu m e o f z i n c i n t h ejo i n t , wh i c h g e n e r a t e s a v e r y l im i t e dquant i ty of l iquid to f i l l the jo int .Aluminum wi th O ther E lements

The literature records other at temptsto deve lop new brazes fo r a lum inum en-gineer ing materia ls , in volv ing the a l lo y-ing o f less usua l e lements w i th a l u -

minum, inc lud ing ca lc ium (Ref. 20) , in -d ium, t in and yt t r ium (Ref . 21) . None ofthese combinat ions has gained accep-tance by indust ry because the proposedbrazes suf fered f rom def ic iencie s that in-c lude infer ior mecha nical propert ies, apropens i t y t o cor rode when in con tac twith a lum inum , excessive eros ion of thebase meta ls dur ing the b raz ing cyc le ,and the lack of to lerance of the jo in ingopera t ion to var ia t ions in t he p rocesscond i t ions .Ternary Al loys of A luminum

Add ing a th ird consti tuent to an a lu-minum al loy can achieve fur ther reduc-t ions in the m elt ing po int . Thus , there arelow me lt ing point ternary eutect ics in thea lu m in u m - s i l i c o n - s i l v e r ( Re f. 2 2 ) a nda lum inum-copper -s i l i con sys tems (Ref .23) , at 563C (1045F) and 524C(975F), respect ively. H ow ever, alloy s ofeutect ic composi t ion a lso contain re la-t ive ly large volu me f ract ions of the inter -metal l ic phases Ag2AI and AI2Cu, re-spect ively, w ith th eir attendant problems.The e mb r i t t l ing phase s can be s ide-stepped by preparing the braze as a foilo f a lum inum -s i l i con w i th a th in c ladd ingo f s i l ve r o r copper . P rov ided tha t t hecladding is no more than a few micronsthick, these preforms can be used to joina lu m in u m b y a d i f f u s i o n s o ld e r in gprocess (Ref. 24). The copper layers wil lcomple te ly d i f f use ou t o f t he jo in t andinto the a lumin um components i f the as-semb ly is held at the braz ing temperaturefor more than four hours. A shorter t imeat the jo in ing temperature wi l l generatet h e u n d e s i r a b le a l u m in u m - c o p p e rphases so that this approach is on ly suit-able for a rest ric ted numb er of a lum inumcast ing alloys. Joint strengths exceeding225 MPa (33 x 103 ps i) have beenachieved in cast ing a l lo y type A356 .0 bythis method (Ref. 24).O ther a lum inu m te rnary a l loy combi -nat ions with s i l icon, germanium, s i lver ,copper, magnesium and z inc were ex-amined , but a l l suf fered f rom one o r moreof the drawbacks encountered with thebinary a l loys (other than aluminum-si l i -con) . The search fo r nove l a lum inumbrazes was therefore e xtended to quater-nary a l loys.Investigation o f Q uaternaryAl loy Systems

In emb ark ing on a study of quaternaryal loys of a luminum , we w ere confrontedwith a dear th o f publ ished data on thesea l loy sys tems. Dete rm in ing the phaseequ i l ib r ia f o r an a l loy sys tem o f morethan two com ponents is an arduous task,

even when the cons t i t uen t b inary sys -tems are know n. T herefore, it was neces-sary to de velo p a focused st rategy forrap id ly exam in ing qua te rnary a l loy sys-tems, but mainta in ing a h igh degree ofprec is ion and accuracy. By l imit ing theinit ial scanning procedure to the essen-t ia l parameters of a candidate a l lo y ( i . e . ,l iqu idu s temperature, me lt ing range andme cha nical propert ies), i t was possible tores t r ic t t he labora to ry inves t iga t ion towith in manageable propor t ions. Compo-sit ions tha t came clos e to meet ing the tar-ge t c r i t e r ia were then eva lua ted mores p e c i f i c a l l y as b ra z e s , m a k in g m in o rchanges to the comp osi t ion, as approp r i -ate, in an attempt to achieve the desiredbalance of propert ies.The con st i tut ional features of 19 qua-ternary a l lo y systems were appraised byseveral methods in tandem. C alor im et r ictherma l ana lys is , t o measure l iqu idusand solidus temperatures (Refs. 25 -27), astat ist ical interpolat ion technique to pre-d ic t compos i t ions hav ing a nar row me l t -ing range (Ref. 28) and quant itat ive met-a l l o g r a p h y s u p p le m e n t e d b y x - r a ym ic roana lys is in an SEM was used toident i fy the phases present in a g ivenal loy (Ref. 29). Co l lect ive ly , thes e deter-minat ions establ ished the shape of thel iqu idus and so l idus sur faces toge therwith the pr ima ry phase in each region,us ing a minimal number of a l loys (Ref .30). Hardness measuremen ts on thesame al loys were used to produce a rudi-mentary map o f mechan ical propert ies asa func t ion o f a l loy compos i t ion . F romthese data it was then po ssible to ide nt ifycom posi t ion ranges that warranted moredetai led invest igat ion.Identi f ication of Candidate Al loys

A reasonable basis on w hich to bui lda n o v e l m u l t i c o m p o n e n t a l u m i n u mbraze is t he a lu rn inum-s i l i con eu tec t ical loy. This composi t ion and those c loseto it meet all of the target requirements,w i t h t h e e x c e p t i o n o f m e l t i n g p o in twh ich is too h igh for most appl icat ions.The add i t ion o f copper depresses themel t ing po in t o f a lum inu m-s i l i con a l loysto a minim um of 524C (975F) (Ref. 23) .However , t he concent ra t ion o f copperthat is needed to s imultaneously main-ta in a nar row melt ing range is suf f ic ientto generate a large volum e f ract ion of theh a rd A I 2Cu i n t e r m e t a l l i c c o m p o u n d .This makes the a l loy b r i t t le and reducesits corrosion resistance so as to rend er itunusable as a braze. A study was ca rr iedout to id ent i fy a quaternary addi t ion thatcould par t ly subst i tute for copper to im-prove the me chanica l propert ies and cor -ros ion res is tance , bu t w i t hou t s ign i f i -

W E L D I N G R E S E A R C H S U P P L E M E N T I 2 4 5 - s


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2 0 0 i

oot Z /ooi t v

60 0

57 5

55 0

5 2 5

0 L i i t I0 1 0 2 0 3 08 8 A I - 1 2 S l w t % c o p p e r

F i g. 1 - - H a r d n e s s a n d l i q u i d u s t e m p e r a t u r e o f a l u -m i n u m - c o p p e r - s i l ic o n a l lo y s a s a f u n c ti o n o f c o p p e rc o n c e n t r a t i o n .

50 0

cant ly a l ter ing the me lt ing range of the a l-loys. Pr ior i ty considerat ion was given toelements adjacent to copper in the Peri-odic Table, in pa r t icu lar s i lver and n ickel ,on the grounds that the p hase re lat ion-ships of these elements with a luminumand s i l icon are s imi lar to those of copper(Ref. 31). The other elements adjoiningcopper in the Per iodic Table were notg i v e n p r i o r i t y c o n s id e r a t i o n a s m a jo rcons t i t uen ts o f t he new braz ing f i l le rm e t a l a l l o y : z i n c a n d c a d m iu m a r evola t i le and therefore not sui table for fur -nace b raz ing , par t icu la r ly a t reducedpressure, wh i le p al ladiu m was judged tobe too expens ive . I t was an t ic ipa ted ,therefore, that the introduct ion of smallpercentages (


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" t ' < . , 4 -I + + ~ ~++' " . '* " ' L ~ , _ , , . ,F ig . 3 - - M i c r o s tr u c t u re o f a n a l l o y o f c o m p o -s i ti o n 7 3 A I - 2 0 C u - 2 N i - S S i ( w t- % ) p r e p a r e d b yc o o l i n g s l o w l y f r o m a b o v e t h e l i q u i d u s t e m -p e r a t u r e ( 1 0 0 ) 0 . T h e ph a s e s p r e s e n t a r e : 1 ) A I ,2 ) A I2 Cu, 3 ) A I6Cu3Ni , 4 ) S i .

7 ~ , , . + , " f ,F i g. 4 - - M i c r o s t r u c t u r e o f t he 7 3 A I - 2 0 C u -2 N i - 5 S i ( w t - % ) a l l o y , p r e p a r e d i n t h e s a m em a n n e r as d e s c r i b e d i n F ig . 3 , b u t i n c o r p o r a t -i n g 0 . 0 1 w t - % o f s t r o n t i u m a s a g r a i n r e f i n i n ga g e n t ( 1 0 0 ) 0 .

s t r o n t i u m wa s m a d e t o t h e c a n d id a t ebraz ing a l loy a t a concent ra t ion o f about0.01% and the resul t ing microst ructuralref inement that is produced in a sol id i -f ied ingo t o f t he a l lo y can be se en bycompar ing F ig . 3 w i t h F ig . 4 .The na t ive ox ide layer on a lum inumeng ineer ing a l loys and a lum inum-con-ta in ing braz ing fo i ls is suf f ic ien t ly tena-c ious to l im i t t he f lu id i t y o f t he m o l tena l loy . Two approaches have been de-v ised to overcome th is problem. One isto use magnesium vapor to remove thealum ina f rom the jo int sur faces and alsothe f i l le r meta l . The mechan ism o f re -mova l invo lves a combina t ion o f phys i -cal and chemical ef fects and has beenstudied exten sively (Refs. 8, 3 7-39 ) . Themagnesium may be int roduced e i ther asa metal charge in the furnace placed ad-jacen t the jo in t o r by be ing a l loyed to t hebraze o r t he base mater ia l . For t heprocess to work , the furnace atmospheremust be a good vacuum (base pressure


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Tab le 2 - - Recom m ended Process ing Condi tions fo r Us ing the N ew Candidate BrazesParameterBrazing temperatureTime at brazing temperatureHeating rate to brazing temperatureFurnace atmosphere

Value>525C (978F)>1 min>2C /min (3.6F/min)Inert


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t e s t a r e a lm m

6 0 m m

Fig. 10 - - Geom et ry o f the tes t p ieces adoptedfor ewf luat ing the shear s t rength o f o ints rnade~u s i n g t h e n e w l o w - m e l t i n g - p o i n t b r a z i n gal loy.C o n c l u s i o n s

A q u a t e r n a r y a l u m i n u m a l l o y h a v in gt h e c o m p o s i t i o n 7 3 A I - 2 0 C u - 2 N i - 5 S i ( w t -% ) , w i t h subpercen t age add i t i ons o f S r ,B i, Be , has been deve l ope d as a new l ow -m e l t i n g - p o i n t b r a ze , p r i m a r i l y f o r j o i n i n go f a l u m i n u m e n g i n e e r i n g m a t e r ia l s . T h ea l l o y c o n t a i n s m i n o r a d d i t i o n s o f s e -l e c t e d e l e m e n t s w h i c h p r o m o t e w e t t i n gand a f f ec t g ra i n re f i nemen t . A f l ux l essj o i n i ng p rocess has been es t ab l i shed f o rus i ng the b raze i n i ne r t gas and v acu umf u r n ac e s a t te m p e r a t u r e s d o w n t o 5 2 5 C(977F ) . Th i s p roduces we l l - f i l l ed j o i n t sw i t h s m o o t h , r o u n d e d f i ll e ts a n d m i n i m a le ros i on o f t he base ma t e r i a l . The b razec a n b e p r e p a r e d i n t h e f o r m o f f l e x i b l ef o i l e it h e r b y c h i l l - b l o c k m e l t - s p i n n i n g o rb y r o l l - b o n d i n g l a ye r s o f a l u m i n u m - s i l i -c o n a n d c o p p e r - n i c k e l a l l o y s i n a n a p -p r o p r i a t e t h i c k n e s s r a t i o . T h e s h e a rs t reng t h o f s i mp l e l ap j o i n t s a re compa-rab l e t o t ha t o f base me t a l s , depend i ngo n t h e i r s p e c i fi c c o m p o s i t i o n a n d m e t a l -l u rg i ca l cond i t i on . Jo i n t s made t o eng i -n e e r i n g a ll o y s o f a l u m i n u m a p p e a r t o b ee n d o w e d w i t h a n a p p r e c i a b l e r e s is t an c et o g a l v a n i c c o r r o s i o n .

Therefore, in most respects , the or ig i -n a l o b j e c t i v e s w e r e s u b s t a n t i a l l y

a c h i e v e d , n a m e l y a n e w a l u m i n u n lb r a z e v v a s d e v e l o p e d h a v i n g a s i g n i f i -c a n t l y r e d u c e d m e l t i n g p o i n t w h i c h p r o -d u c e s w e l l f i l l e d j o i n t s w i t h a l u m i n u me n g i n e e r i n g a l lo y s o f i n te r e s t, w i t h o u ti m p a i r i n g t h e i r m e c h a n i c a l a n d e n v i r o n -m e n t a l c h a r a c t e r is t ic s t o a n y a p p r e c i a b l edegree . The cons t i t uen t s o f t he b raze a rel o w c o s t , a n d t h e a l l o y c a n b e r e a d i l yp roduced as a f o i l su i t ab l e f o r p re f o rms .T h e g o a l o f f lu x l e ss b r a z i n g w i t h t h e n e wa l l o y w a s a t t a in e d , a n d t h e r e q u i r e m e n t son t he p u r i t y o f the p ro t ec t i ve n i t rogen a t -m o s p h e r e a r e r e a d i l y a c h i e v a b l e , u s i n gr e l a t i v e l y s im p l e e q u i p m e n t . T h e u l ti -ma t e cos t o f t he b raz i n g a l l oy i n the f o rmo f a f o i l , and t ha t o f ope ra t i ng t he b raz -i ng process , w i l l m os t l y depen d on t hee c o n o m i e s t h a t c a n b e e s t a b li s h e d i n v o l -u n l e p r o d u c t i o n .

A c k now l edgm en t sT h i s p r o j e c t w a s p a r t l y f u n d e d b y t h eC o m m i s s io n o f t h e E u r o p ea n C o m m u n i -

t ie s w i t h i n a B R I T E /E U R A M c o l l a b o r a t i v ep r o g r a m ( P r o j ec t N o . 3 0 8 2 - 9 0 ) . T h e p r o -j e c t p a r tn e r s w e r e G E C - M a r c o n i M a t e r i -a ls Te ch no log y Ltd. (UK), CLA L (France),Dorn i e r Lu f t f ah r t (Germany) , VAW (Ger -m a n y ) a n d I P L - T N O ( N e t h e r l a n d s ) a n dt h e i r c o n t r i b u t i o n t o t h e e x p e r i m e n t a lp r o g r a m is g r a te f u l ly a c k n o w l e d g e d . T h eshear s t reng t h measuremen t s c i t ed weremade by A . A run Juna l a t TNO, and t hec o r r o s i o n t r i a l s w e r e c o n d u c t e d b y H .Schoer a t VAW .

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cast versus conv ention al die attach soft sol-ders. IEEE Transact ions on Comp onents, Hy-br ids and Manufac tur ing Technology 10(3):341-345.36. Hellawell, A. 1979. The Growth andStructure of Eutect ics wi th Si l icon and Ger-manium, Progress n Materials Science 15(1 ,Eds. B. Chalmers, I. W. Christian, and T. B.Massaiski, Oxfor d, Pergamon Press.37. Winterbottom, W. L., and Gilmou r, G.A. 1976. Vacuum brazing of aluminum: augerstudies of wetting and flow characteristics.Journa l o f Vacuum Sc ience and Technology13(2): 634-64 3.38. Anderson, W. A. 1977. The effects ofmetallurgical structure on the brazing of alu-minum. Proc . Syrup. Physical Metal lurg y o fJoining Metals , Warrendale, Pa., TMS-AIME,Eds. R. Kossow sky and M . E. Glicksman , pp.222-243.39. Takemoto, T., and Okam oto, I. 1988.Effect of magnesium content in brazing sheetcladdings on the vacuum brazeablity of alu-minum in relatively enclosed volumes, Braz-

ing a nd Soldering 15(3): 32-36.40. Schultze, W., and Schoer, H. 1973.Fluxless brazing of a lum inum using protectivegas. Welding Journal 52(9): 644-65 1.41. Gem pler, E. B. 1976. P arameters eva l-uated in long cycle aluminum vacuum braz-ing. Welding Journal 55(10): 293-s to 301 -s.42. Ashburn, L. L. 1983. Furna ce designconsiderat ions for aluminum brazing undervacuum, Welding Journal 62(10): 45-54 .43. Singleton, O. R. 1970. A look at thebrazing of aluminum - - part icularly f luxlessbrazing. Welding Journal 49(11 ): 843- 849 .44. Terrill, J. R., eta l . 1971. U nderstandingthe mechanisms of aluminum brazing. Weld-ing Journa l 50(12): 833-839 .45. Heine, B., and Sahm, K. F. 1993.Flussmittelfreis hartl6ten luftfahrtrelevanteraluminumlegierungen mit niedrigschmelzen-dem lot. Schweissen und Schneiden 45:429-430.46. Pr ivate communicat ion f rom VAW,Bonn, Germany.

A m e r i c a n S t u d e n t R e s e a r c h e r sGo for S ix in S ix YearsU . S . H as C l a i m ed F i v e I n t e r n a t i o n a l

G ran jon Pr izes in F ive YearsSep t ember 30 w i l l be t he dead l i ne f o r rece i p t o f cand i da t e papers f o r t he p re l i m i na ry na t i ona l compe t i t i on f o r t he 1997

I n t e rna t i ona l I ns t it u t e o f W e l d i ng 's ( I I W ) Henr i G ran j on P r i ze Com pet i t i on f o r i nd i v i dua l l y au t ho red s t uden t research papers .Each o f ll W 's 39 mem ber coun t r i es i s encouraged t o ho l d a na t i ona l comp e t i t i on i n t h ree ca tegor ies , subm i t t i ng t he w i nn er

i n each ca t egory t o t he i n t e rna t i ona l c omp e t i t i on .A l ready p repared Sen i o r papers o r g radua t e theses may be app rop r i a t e f o r t h i s i n t e rna t i ona l comp e t i t i on . Papers a re to beno m ore t han 10 pages l ong , devo t ed t o research i n we l d i ng t echn o l ogy o r a re la t ed sub j ect , f a l l i ng i n t o one o f t hese t h reecategor ies:

Ca t egory One : Des i gn and S t ruc tu ra l In t eg r it y , i nc l ud i ng Nond es t ruc t i ve Exam i na t i onCa t egory Two : Ma t e r i a l s Behav i o r and W e l dab i l i t yCa t egory Th ree : Jo i n i ng and Fab r i ca t ion Tec hno l ogy o r Sub j ec ts Con cern i ng E conom i cs , Hea l t h , Saf et y, Educa t i on , o r

Te rm i no l ogy Assoc i a t ed w i t h Th i s Techno l ogy .Add i t i ona l i n f o rma t i on may be ava i l ab l e f rom co l l ege o r un i ve rs i t y Ma t e r i a l s Sc i ence o r W e l d i ng Depar t men t s , o r by

con tact in g the Tech nica l Papers Edi tor , Am er ic an W eld ing Society , a t 550 N. W. LeJeune Road, Miam i , FL 3312 6, a t faxnum ber 305 -4 42-745 1 , o r a t e -ma i l add ress f re t we l l @a mwe l d . o rg .

Sankaran Subraman i am, W es t V i rg i n i a Un i ve rs i t y , w i nn e r i n Ca tegory 3 , and T racy W . Ne l son , t he Oh i o S ta te Un i ve rs i t y ,co - w i nn er i n Ca t egory 2 , w i l l be p resen ted t he i r G ran j on P r i ze awards a t t he I I W An nua l Assemb l y nex t mon t h i n Budapes t,Hungary . Subraman i am 's work , t i tl ed " W i re Feed Ra te Mod e l f o r Pu lsed Gas Me t a l A rc W e l d i ng o f A l u m i nu m" desc r i bed h i sdoc t o ra l wo rk comp l e t ed i n con j unc t i on w i t h t he Fo rd Mo t o r Com pany . Ne l son 's paper , t i tl ed " I mprove d C i rcu l a r Pa tch TestP rocedure f o r Assess ing W e l d So l i d i f i ca t i on C rack i ng " , t o l d o f wo rk done f o r h i s Mas t e r 's o f Sc i ence Degree i n W e l d i ngEnginee r ing. Both are no w em ploy ed as graduate research ass is tants .

I n 1994 , Zh i l i Feng, t he Oh i o S ta te Un i ve rs i t y , won t he Gran j on i n Ca t egory 2 f o r h i s doc t o ra l research on " ACom put a t i ona l Ana l ys i s o f The rma l and Mec han i c a l Cond i t i ons f o r W e l d Me t a l So l i d i f i ca t i on C rack i ng . " He rece i ved hi saward a t t he I I W Ann ua l As semb l y i n Be i j i ng , Ch i na .P roba l Baner jee , Aubu rn Un i ve rs i t y , rece ived t he 1993 Gra n j on i n Ca t egory 3 i n G lasgow, Sco t l and . H i s paper , " G rad i en tTechn i que f o r On- L i ne W e l d Bead W i d t h C on t ro l , " desc r i bed w ork co mp l e t ed i n pu rsu i t o f h is doc t o ra l deg ree .

In it s inaug ura l year, Wa ngen L in , a docto ra l s tud ent a t the Oh io State Un iver s i t y a t the t ime, ea rned the 199 2 G ran jon inCa t egory 2 f o r h is paper " A Mod e l f o r HA Z L i qua t i on C rack i ng . " He was p resen t ed h is award i n Madr i d , Spa i n .

a new low-melting-point aluminum braze

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