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MECHANISM OF EXPLOSIVE WELDING OFMETALS

W. Sek

To cite this version:W. Sek. MECHANISM OF EXPLOSIVE WELDING OF METALS. Journal de Physique Colloques,1988, 49 (C3), pp.C3-371-C3-377. �10.1051/jphyscol:1988353�. �jpa-00227776�

JOURNAL DE PHYSIQUE Colloque C3 , Suppl6ment au nag, Tome 49, septembre 1988

MECHANISM OF EXPLOSIVE WELDING OF METALS

W. SEK

I n s t y t u t Techniki C iep lne j , ~ b d i , u l . Dabrowskiego 113, Poland

~ 6 s u m 6 - On d i s c u t e l e m6canisrne de soudage exp los i f . Des r6su;; ?Z?Z-Zxp&rimentaux montrent que l a su r f ace de l i a i s o n e s t formee apr& l e passage du p o i n t de c o l l i s i o n $t,que ce processus ,es t a f f e c t e considerablement ,par des ,p rop r i e t e s physiques de metaux. On met en doute l ' u t i l i t e du modele hydrodynamique pour l a des- c r i p t i o n du processus de soudage explos i f .

Abs t r ac t - Mechanism of explos ive welding is discussed. The ex- ------- perlmenTal d a t a i n d i c a t e t h a t t h e explos ive bonding i n t e r f a c e forms behind t h e c o l l i s i o n po in t and the phys i ca l p r o p e r t i e s of me ta l s a f f e c t cons ide rab ly t h i s process. The usefu lness of hydrodynamic model f o r d e s c r i b i n g t h e explosive welding process i s ca.lled i n ques t ion .

with t he i nc rease of t he i nyac t a n g l e p . This phenomenon i s r e a l l y observed i n explos ive welding of metals, when t h e p re set-up ang led ) /O . There e x i s t , however, some experimental dats. which d isaccord t h e r e s u l t s ca l cu l a t ed on t h e base of t he hydrodynamic theory. I t has been proved t h a t the wave lenght llI~lf i nc reases i n s n i t e of t he decreLd!fis2Iipact angle f i , when s tudying t h e explos ive welding arocess with t h e negat ive o re

1 - INTRQIUC!IGE During t h e l a s t year , t h e process of explos ive welding has been ex tens ive ly s tud i ed . A s f o r t h e experimentaly confirmed l i m i t i n g values of welding parameters , t h e r e i s , i n p r i n c i p l e , uniformity of view i n t h e mids t o f i n v e s t i g a t o r s . However, some r a d i c a l d i v e r - gences e x i s t i n t h e way of t h e explana t ion of explosive welding phenomena and p a r t i c u l a r l y of t h e wave formation. Some au tho r s ,7,3) aonsides, t h a t t h e j e t ex i s t ence i s no t a precondi t ion f o r acceptable weld. They a t t r i b u t e t h e g r e a t p a r t played by p l a s t i c deformation o r i g i n a t i n g i n t h e impact of elements i n t h e reg ion of c o l l i s i o n poin t . This l e a d s t o t h e ex i s t ence of p l a s t i c zone connect& with t h e pa ren t p l a t e . However, t h e most of t he i n v e s t i g a t o r s consider t h a t t h e formation of j e t from both sur faces (from (3+6 ,9 ) the pa ren t and f l a y e r p l a t e ) is the precondi t ion of an acceptable weld. The curves A and B i n t he F igure 1 a r e t he l i m i t s o f t he j e t formation area . This i s based on t h e hydrodynamic theory and each

process which l eads t o t h e forma- t i o n of a bond i s considered a s

Bid' a impact of such j e t s , disregard-

0.8 . 0.7. 0.6. 0.5. 0.4. 0.3 . 0,2 . 0.1.

i ng , i n p r i n c i p l e , t h e phys ica l p r o p e r t i e s of bonding ma te r i a l s . I n consequence i t is s a i d t h a t , t h e bond i s forming i n t h e neigh- bourhood of c o l l i s i o n po in t and t h e problem of wave bond forming i s reduced t o desc r ib ing flow non- A T s t a b i l i t y . PL hydrodynamic model descr ibed i n o e r n i t s t o

fOW 2000 3000 4000 f i n d s o m e (3,596)experimental- '' a n a l y t i c r e l -%t ionsh ips of process Fig.1. The j e t formation area parameters. It i s shown, t h a t t he

l e n ~ h t of wave I1Lu should i nc rease

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1988353

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set-up ang leoc o f s u r f a c e s t o b e bonded Furthermore, measure - ments o f t h e c o l l i s i o n p o i n t v e l o c i t y &($?&ormed u s i n g a method of s h o r t e n i n g r e s i s t a n c e , have shown t h a t t h e j e t d i d n o t e x i s t , a l t h o u ~ h , t h e a c c e p t a b l e weld h a s been ob ta ined . S imul taneous ly , t h e o b t a i n e d r e s u l t s a l lowed t o suppose, t h e p l a s t i c a l l y deformed m e t a l i s s h i f t e d by t h e f l a y e r p l a t e i n f r o n t o f t h e c o l l i s i o n p o i n t . Th is m e t a l is i n t h e l i q u i d s t a t e . I t h a s been p r ~ v e d i n t h a t t h e welding s u r f a c e s a r e connected th rough t h e t h i n l aye413bi mol ten and r e c r y s t a l i z e d m e t a l . The m i c r o d i f f r a c t i o n p a t t e r n s o f t h i s l a y e r have shown t h a t i t had 2 c r y s t a l s t r u c t u r e w i t h o u t any t e x t u r e . The a n a l y s i s of t h e s e r e s u l t s l e a d s t o a c o n c l u s i o n , t h a t t h e f i n a l s t a t e o f welding bond i s n o t formed i n t h e r e g i o n o f c o l l i s i o n p o i n t b u t i n a long d i s t a n c e behind t h i s p o i n t . Provided t h e v e l o c i t y i s 4=2000 m / s , t h e c o l l i s i o n p o i n t c o v e r s a d i s t a n c e o f 2 mm d u r i n g ips . Tf a bond were formed n e a r t h e c o l l i s i o n p o i n t , t h e t empera ture of molten zone would have t o lower a b o u t 100-1000 R d u r i n g 1 ~ . Th is w o ~ l d 5 e c u i r e t h e v e l o c i t y of t h e t empera ture d e c r e a s e e q u a l t o a b o u t 10 -10 k/s and should l e a d t o t h e amorphous s t r u c t u r e s . On t h e o t h e r hand, t h e a ~ t u a l ~ c r y s t a l s t r u c t u r e i n d i c a t e s , t h a t t h i s v e l o c i t y d i d n ' t exceed 10 K/s . Thus, f i n a l forming of t h e bond t a k e s a t ime of t e n s microseconds and i n t h i s o e r i o d t h e c o l l i s i o n p o i n t i s s e v e r a l hundred m i l i m e t e r s d i s t a n t from a p o i n t o f m a t e r i a l bonding.

I t h a s been s a i d a l r e a d y t h a t t h e weld bond forming is connected w i t h t h e e x i s t a n c e o f l i q u i d phase , and t h e f o r m a t i o n t ime l a s t s a t l e a s t t e n s of microseconds. TRus t h e p h y s i c a l p r o p e r t i e s o f bond- i n g m a t e r i a l such as t h e m e l t i n g p o i n t , the rmal c o n d u c t i v i t y and e l a s t i c i t y , must p l a y a g r e a t p a r t i n t h i s p rocess . I n o r d e r t o i n v e s t i g a t e t h i s s u ~ p o s i t i o n and t o i n v e s t i g a t e whe ther t h e l a y e r o f m e t a l s h i f t e d i n f r o n t o f t h e c o l l i s i o n p o i n t o r i g i n a t e d from t h e p a r e n t o r f l a y e r late t h e f o l l o w i n g exper iment was c a r r i e d o u t . Two i d e n t i c a l , unsymmetrical s l e e v e s , t h e f i r s t o f t h m made from 8 t h e s t a i n l e s s s t e e l 18.8 (Young's modulus E=l 96 x 10 M?a) and t h e second from t h e aluminium bronze (E=1 , C 3 x 1 0 3 ~ 2 a ) were p repared t o f a s t e n i n s i d e s t a i n l e s s s t e e l 18.8 t u b e s (16 mm d i a , 1 ,2 mm w a l l t h i c k n e s s ) u s i n g t h e i d e n t i c a l e x u l o s i v e charges . The shock a d i a - b a t e s o f t h e s t a i n l e s s s t e e l 18.8 and t h e aluminium bronze a r e n e a r l y t h e s m e , t h u s t h e p r e s s u r e i n t h e impact r e g i o n should be slmllar. F i g u r e 2 shows t h e d e t a i l e d model and t h e p l a n e s where t h e meta lograph ic specimens were c u t from. The unsymmetr ical f l a n g e

Pig.2. The model f o r exper iments and t h e p l a n e s c u t o f them

01, the stainless steel 18-8 sleeve - 460

. J

>['. ..;->>;. .;- .,. . :,,>. , . . \ . .

D- wave bond UDIUIl! - flat bond

b) the brass sleeve - x 160

C3-374 JOURNAL DE PHYSIQUE

(16 mm d i a . ) was made t o s t o p a l l t h e elements be ing s h i f t e d before t h e c o l l i s i o n po in t i n t h e bonding zone. The de tonat ion v e l o c i t y wa.s equal t o D=6300 m / s and consequently, t h e a x i a l component o f impact v e l o c i t y Vk exceeds t h e va lue of son ic v e l o c i t y i n meta ls t o be bonded. Con t ra r i l y , t h e c i r cumfe ren t i a l component o f Vk was subsonic on t h e n e a r l y whole length . The r e s u l t s a r e shown i n Pig.3. I n o rde r t o q u a l i f y .the chemical compos.ition o f l a y e r which i s s h i f t e d i n f r o n t of t h e c o l l i s i o n p o i n t i n t h e p lane , t h e microanalys is ( l i n e and s u r f a c e ) was done ( ~ i g . 4 ) . The obtained r e s u l t s showed, t h a t t he s h i f t e d l a v e r c o s i s t a of comoonents of t h e bronze s l e e v e wi th

distribution of Cr

Pig.4. The microanalys is of t he l a y e r s h i f t e d i n f r o n t of t he c o l - l i s i o n p o i n t

a incons iderable amount of oxygen o r i g i n a t i n g probably from the l a y e r of oxides. A l i t t l e i n c r e a s e of chromium and n i c k e l concentra- t i o n was observed only i n a very t h i n zone ad jacen t t o t he tube ma te r i a l . Thus t h e l a y e r s h i f t e d i n f r o n t of t he c o l l i s i o n po in t , i a a p a r t of s l e e v e m a t e r i a l and it does no t show the na tu re o f a j e t i because then t h e concent ra t ion of chromium and n i c k e l should be g r e a t e r and ranged deeply i n t h i s layer . This was a l s o confirmed i n another experiment. The tube was fas tened i n the s l eeve a t t h e pre s e t a n g l e d = 3 (k)O). The explos ive cha.rge was ended a t t he range of cone as i t is shown i n Fig.5a. Two zones may be d i s t i ngu i shed

-- -

lhe re~ioo on the Fiq 5b

Pig.5: The scheme of experiment and s t r o n g l y deformed l a y e r o f s leeve

i n t h e obtained bond: - wave zone bond - f l a t bond zone. Its end corresponds with t h e end of t he explos ive charge - Fig.5b

I n Fig.5b t h e s t rong ly p l a . s t i c a l l y deformed l a y e r of s l eeve ma te r i a l

can be seen. Th is l a y e r would have been removed from t h e bond by

flajrer t u b e w a l l , i f t h e e x p l o s i v e charge had been longer . So s t r o n g - l y p l a s t i c a l l y deformed r e g i o n s were n o t found w i t h i n t h e bonding zone. L e t u s n o t i c e , t h a t t h i s s t r o n g deformat ion i s conf ined t o a t h i n t o p l a y e r of s l e e v e m a t e r i a l . The t h i c k n e s s o f t h i s l a y e r i s 15 ; 20 m. P The f o l l o w i n g s n e c i f i c d e t a i l s can b e n o t i c e d i n t h e ob ta ined r e s u l t s - The s t e e l 18.5 s l e e v e does n o t show any c r a c k s on i t s t o p s u r f a c e

a f t e r t h e e x 3 l o s i v e f a s t e n i n g of a tube. The same bond s t r u c t u r e i s observed on t h e s l e e v e c i rcumference i n t h e ? l a n e d , and on b'oth s i d e s o f t h e n l a n e d . R e s u l t s a r e d i f f e r e n t f o r t h e bronze s l e e v e . A few c r a c k s were observed i n t h e p lane 8 e s well a s on

the l e f t s i d e o f t h e s l e e v e . The wave bond e x i s t s on ly on t h e r i g h t , undemaged s i d e . On t h e l e f t s i d e t h e e x i s t i n g bond h a s a f l a t c h a r a c t e r a l o n g t h e whole c i r c ~ m ~ f e r e n c e . - The e x n l o s i v e bond t o t h e bronze s l e e v e shows i n t h e p l a n e d , t h e cons iderab ly g r e < + t e r v a l u e s o f t h e wave l e n g t h , t h e ampli tude and t h e i r r a t i o when comnaring with t h e s l e e v e made from s t e i n l e s s s t e e l 18.0 ( i n s n i t e o f t h e same paramete rs of t h e e x p l o s i v e p rocess ) . D i f f e r e n c e s o f 2hysical . ? r o n e r t i e s o f t h e s l e e v e ma . te r ia1 cnn b e c h a r a c t e r i z e d by: 77

-'in 0 1 0 . : m t i o o f , oung's moduli -;----- =

"bronze

r a t i o of m e l t i n g ~ o i n t s ------- -

r a t i o o f termal c o n ? u c t i v i t i e s :/-bronze/:~19.q > 11 - In b o t h c'tses t h e f l a t bond :vna obta ined a t /$,,;,'k. 3'. For t h e

s t a i n l e s s s t e e l 18.4 s l e e v e , t h e minimum i n i t i a l gap a t which the f l a t bond h a s been o b t - i n e g , was e ~ u a l t o %,,*0,54 mm, t h e wave bond s t a r t e d a t ;,) 1 , C 5 mm and /3a6,3O a n 3 f i n i s h e d a t So% 1.65 mm and /3%4O . For t h e bronze s l e e v e : &,,,,;, ';YN C,15 mm, the wave bonding s t a r t e d a t So= C , 2 m m , nN 3,5' and f i n i s h e d a t 3,* 1 , l rnm, f l*6,5*. - The i n t e r f a c e between t h e s u b s t r a t e mr l te r ia l and t h e m a t e r i a l

l a y e r which 1 s s h i f t e d i n f r o n t o f t h e c o l l i s i o n m i n t (F ig . 6 ) as w e l l a s a sphe - r i c a l shape o f c r d t e r s (dark s p o t s ) i n s i d e t h i s l a y e r , t e s t i f y t h a t t h e s h i f t e d m a t e r i a l i n t h e r r e a t p a r t i s i n l i o u i d s t a t e . Thus t h e t e m ~ e r n t u r e of t h i s l a y e r had t o b e h i g h e r than 13CO 1:. The above d a t a p o i n t , t h a t t h e f o l l o w i n g m a t e r i a l ~ r o ~ e r t i e s a f f e c t t h e wave l e n g t h and i t s ampli tude: a t h e m e l t i n g p o i n t b t h e thermal c o n d u c t i v i t y c I t h e d i f f e r e n c e s of e l a s t i c recovery o f t h e

m a t e r i a l s t o b e bonded. Thev a r e r e p r e s e n t e d x 63 by "oung9s moduli , b u t t h e y V d e ~ e n d a l s o on

Fig.6. The m z t e r i a l t h e s t a t e o f load ing . -

s h i f t e d i n f r o n t o f t h e c o l l i s i o n p o i n t

A s t r o n g p l a s t i c de format ion occurs i n t h e r e g i o n of c o l l i s i o n p o i n t during t h e impact of m a t e r i a l s . A s u i t a b l e r a t e o f t h i s deformat ion,

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d e f i n e d by t h e imgact v e l o c i t y V and t h e v e l o c i t y o f c o l l i s i o n p o i n t , e n s u r e s tha.t t h e p r o c e s s i s a d i a b a t i c and t h e h e a t emiss ion t o t h e t h i n t o p l a y e r o f s u b s t r a t e i.s l i m i t e d . I t c a u s e s m e l t i n g o f t h i s l a y e r . I n consequence, a t t h e same c o n d i t i o n s , t h e t h i c k n e s s o f t h e l a y e r b e i n g molten and ~ 1 a . s t i c a l l y deformed w i l l b e g r e a t e r i f t h e m e l t i n g p o i n t o f t h i s m a t e r i a l is lower and t h e the rmal c o n d u c t i v i t y i s h igher . The imuact v e l o c i t y s u f ~ l c i ~ n t f o r a n a c c e p t a b l e weld w i l l b e a l s o lower a t t h e lower m e l t i n g p o i n t o f s u b s t r a t e m a t e r i a l . EIence, t h e a c c e ~ t a b l e weld w a s o b t a i n e d f o r b ronze s l e e v e (T ~ 1 3 0 0 K ) a t t h e gap So,, x C,15 m m , whereas f o r s t e e l 18.8 s l e e v e (T W 1700K) on ly when t h e gap was q a 0 , 5 4 mm. The the rmal c o n d u c t i v i t y and t h e e l a . s t i c r e c o v e r y ( c h a r a . c t e r i z e d by Young's modulus) a r e a l s o g r e a t e r f o r hronze t h a n f o r s t 2 i n l e s s s t e e l 18.3 . That i s why t h e l e n g t h and t h e ampl i tude o f waves were g r e a t e r f o r b ronze s l e e v e t h a n f o r 13.8 s t e e l s l e e v e . Furthermore, t h e i n f l u e n c e o f t h e a n g l e f i i n t h e welding n r o c e s s i s worth n o t i c e . The a c c e g t a b l e welds were o b t a i n e d i n b o t h c a s e s a t p,,,,be 3' ( b u t a t d i f f e r e n t i n p a c t v e l o c i t i e s ) i n s p i t e o f f i i f f e r e n c e s i n g h y s i c q l p r o p e r t i e s o f s t a i n l e s s s t e e l and aluminium bronze. I t g i v e s a c o n c l u s i o n t h a t t h e a n g l e f i d o e s n o t a f f e c t bond forming. Cn t h e o t h e r hand t h i s a n g l e i s o f g r e a t irnnortance i n t h e c r a c e s s o f p l a s t i c d e f o r m a t i o n o f t h e t o p l a y e r c r e a t i n g ccnditl ' .ons f o r t h e I.oc:?.lizr?tion o f t h i s de format ion and f o r t h e i n t e n s j - v e h e a t emission. I t s minimum v a l u e determined a s k m * 3 0 is i n t h e good ggreenen t wi th d-itn c o i n t a i n e d i n ( 4 ) . I t was s u g - g e s t e d i n ( 5 ) th7.t t h e l ~ c k of weld f o r VK> Co is connected w i t h t h e shock waves cre:? t ion i n t h e r e g i o n of c o l l i s i o n p o i n t . The r e s u l t s d o n ' t confi rm t h e s e s u p g e s t i o n s . *en i f t h e shock waves e x i s t , t h e y have no i n f l u e n c e on t h e welding bond. Th is conf i rms t h e h y s o t h e s i s t h a t t h e welding bonds a r e fo rming i n a l o n g d i s t a n c e behind t h e c o l l i s i o n 7oj.nt. ,'a u n a c c e ~ t s b l e weld f o r V K > C O i s due t o t h e i m n o s s i b i l . i t y o f i n t e n 2 i v e p l a s t i c de format ions o f m a t e r i a l s .

4 - Co'P:C~'JCIo~?S ----------- 1. The p r o c e s s o f exp1o:;ive weJ.ding of m a t e r i a l s i s c o n d i t i o n e d by

t h e i n t e n n i v e a1as t i . c deform:.ition o f m a t e r i a l s i n t h e r e g i o n of colli:jj.on p o i n t a.nd t h e n resence o f a j e t i s i s n o t n e c e s s a r y .

2. The paramete rs o f t h e e x p l o 7 i v e welding p r o c e s s a r e i n t e n s i v e n o t enough t o d i s r e g a r ? t h e p a r t of s h e a r s t r e s s e s and t o a p p l y t h e hydrodynamic t h e o r y .

3. The im?act ua.rameters (v, Vk,P ) a f f e c t only t h e ins tan ta .neous s t a t e o f m ? . t e r i a l s i n t h e c o l l i s i o n a o i n t r e g i o n . The c h a r a c t e r o f t h e bond deaends on n h y y i c a l p r o p e r t i e s o f bonded m a t e r i a l s . The bond i s forming d u r i n g a ~ e r i o d of a b o u t t e n s t o s e v e r a l hundred microseconds behind t h e c o l l i s i o n p o i n t . A f l a t o r wavy shape cf t h e bond i s a f u n c t i o n of t h e c o n d i t i o n s i n which t h e minimum e n e r p j o f b0f id j .n~ s u r f a c e i s ach ieved .

Bib l iography:

1 . W.Babul - I1Odksz t a x c a n i e metal i . wybuchemfl, Warszawa, WNT 1980. 2. M.A.Meyers, L.E.I!urr - ttShock S!aves and I- ! ighStrain-Rate

Phenomena i n I;eta.lsrr , 7lenum ' ress , New York, 1980. 3 . W.F.Yudinow, !..Ja.!!orotie jew - "Swa.rka wzrywom w m i e t a l u r g i i " ,

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