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MECHANICAL PROPERTIES OF BEAM ELECTRON WELDINGS IN 8090 ALLOY (CP 271)
P. Le Poac, A. Nomine, D. Miannay
To cite this version:
P. Le Poac, A. Nomine, D. Miannay. MECHANICAL PROPERTIES OF BEAM ELECTRON
WELDINGS IN 8090 ALLOY (CP 271). Journal de Physique Colloques, 1987, 48 (C3), pp.C3-
301-C3-306. �10.1051/jphyscol:1987334�. �jpa-00226565�
JOURNAL DE PHYSIQUE
C o l l o q u e C 3 , suppl6ment au n a g , Tome 48, septembre 1987
MECHANICAL PROPERTIES OF BEAM ELECTRON WELDINGS IN 8090 ALLOY (CP 271)
P. LE POAC, A.M. NOMINE a n d D. MIANNAY
CEA, Centre d'Etudes de ~ruyeres-le-chatel, B . P . 1 2 , F-91680 Bruyeres-le-ChStel, France
SUMMARY.
Beam e l e c t r o n weldings b u t t j o i n t s and embedding j o i n t s of T4 and T6 h e a t - t r e a t e d 8090 a l l o y a r e mechanically t e s t e d j u s t a f t e r welding o r a f t e r an a g e i n g t r e a t m e n t (12 hours a t 210°C).
INTRODUCTION.
Aluminium - l i t h i u m a l l o y s have s p e c i f i c r i g i d i t y and s t r e n g t h t h a t make them i n - t e r e s t i n g a s s t r u c t u r a l m a t e r i a l s . Some a p p l i c a t i o n s r e q u i r e welding and t h e welda- b i l i t y of t h e s e m a t e r i a l s have beeh l i t t l e s t u d i e d [I]. So i t was found u s e f u l t o m e c h a n i c a l l y t e s t beam e l e c t r o n weldings of a n aluminium - l i t h i u m a l l o y i n d i f f e - r e n t h e a t t r e a t m e n t c o n d i t i o n s .
MATERIAL.
The m a t e r i a l comes from two 8090 t u b e s 1 m long, e x t e r n a l d i a m e t e r 48 mm and i n t e r - n a l d i a m e t e r 42 mm, one of which being T4 h e a t - t r e a t e d ( s o l u t i o n t r e a t e d ) , t h e o t h e r being T6 h e a t - t r e a t e d ( s o l u t i o n t r e a t e d + 12 hours 210°C a g e i n g ) . Table I g i v e s t h e chemical composition of t h e s t u d i e d m a t e r i a l .
T a b l e I - Weight chemical composition of t h e s t u d i e d m a t e r i a l ( r e f e r e n c e 1294).
I n each t u b e , a r i n g (60 mm l o n g ) i s machined f o r t h e s t u d y of t h e base m a t e r i a l . H a l f - r i n g s machined and welded w i t h t o t a l p e n e t r a t i o n b u t t j o i n t s ( a ) o r embed- d i n g j o i n t s f 3 ( f o r t h e s t u d y of notch s e n s i t i v i t y ) . F i g u r e 1 g i v e s t h e a s p e c t of t h e two j o i n t s .
I n o r d e r t o determine i f an a g e i n g t r e a t m e n t i s n e c e s s a r y a f t e r welding, t e n s i l e specimens ( t a k e n i n a p a r a l l e l d i r e c t i o n w i t h t h e r i n g a x i s ) are t e s t e d e i t h e r a f t e r welding (T4 and T6 base m e t a l ) o r a f t e r a n a g e i n g t r e a t m e n t of 12 hours a t 210°C (T6 o r "T7" overaged b a s e metal). Specimens w i t h o u t welds a r e t e s t e d i n t h e T4, T6 and T7 h e a t - t r e a t e d c o n d i t i o n s . F i g u r e 2 shows t h e micrographic a s p e c t of
t h e b a s e m e t a l i n t h e s e t h r e e c o n d i t i o n s . S t r a i n r a t e i s E = 10-~.s-l.
( a ) W e l d i n g u n d e r 25 kV v o l t a g e , power of t h e e l e c t r o n beam 800 W f o r b u t t j o i n t w e l d s , and 700 W f o r embedding welds.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987334
JOURNAL DE PHYSIQUE
Tableau I1 - Tensile mechanical properties.
Tableau'III - Hardness measurements under a 20 N load.
Specimen
Base
Metal
With
butt joint
With embedding
joint
With post-welding heat-treatment Heat
treatment condition.
before welding
T4 T6
T4 T6 T4 T6
Material
Base
metal
Heat affected
zone
Weld metal
Base metal condition
T6 T7 T6
T7
T6 T7 5 max
(MPa) (min
450 498 484 / 4 6 5 167 {:::
384 i 3 4 1 403
1 8 0 : 1::
237 ; 1;:
Without post-welding heat-treatment mean value 1%:
%
124 1108 1 5 3 {i::
1 2 1
112 1103
107 1';;
79 i::
Heat treatment condition before welding
T4 T6 T4 T6 T4 T6
Without post-welding heat-treatment
AR max (%) lmin
4.9 5.7 5.5 /5.2
- - -
-
With post-welding heat-treatment mean value { tfE
Hv
1 5 8 (T6) 157 1 154
(T7) 15' 1 1 4 5 158 1 5 8 156 1 1 5 4 1 5 8 154 1 1 4 9 106 1 l;:
128 126 I 1 2 1
$ max (MPa) (min
329 321 /314
443 1::;
290 215 i 1 6 0 325
314 {291
298 ; 1;;
293 283 1273
AR smax (%) (min
9.8 11:.6
5.4 1::;
-
-
-
-
RESULTS.
The results of the tension tests are gathered in table I1 and figure 3 ; hardness measurements under a 20 N load are given in table 111 and figure 4.
In the base metal, ageing treatment (T6) increases hardness and tensile strength and decreases ductility ; an overageing treatment (T7) slightly increases tensile strength but does not change hardness and ductility.
In the welded rings, fracture always occurs in the weld, in the center or on the side of the joint, both with or without a treatment after welding. Just after wel- ding, butt joints or embedding joints have similar behaviors (table I and fi- gure 3) ; ultimate tensile strength (UTS) are 50 X of the base metal UTS in the two conditions T4 ,and T6. After an ageing treatment, the evolution of the mechanical behavior of the velds is complex (table I1 and figure 3) ; an increase or a de- crease of the tensile strength is observed while hardness measurements (table I11 and figure 4) and microhardness measurements (figure 5) show in all cases the har- dening effect of the ageing treatment on the heat affected zone and the weld metal.
Moreover, heat-treatment after welding increases the scattering of the microhard- ness measurements (figure 5).
CONCLUSIONS.
Beam electron weldings were successfully carried out on T4 and T6 heat-treated 8090 alloy. Butt joints or embedding joints have similar mechanical behavior, and there is not notch sensitivity.
A post-welding ageing treatment increases the weld metal hardness but.has an hasar- dous effect on the tensile strength that is made worse in most cases : this treat- ment seems consequently to be forbidden.
REFERENCE.
CROSS C.E., OLSON D.L. and CAPES J.F.
Aluminium-Lithium 11, the Metallurgical Society of AIME (Starke and Sanders Ed.),
1983, p. 675.
C3-304 JOURNAL DE PHYSIQUE
Butt weld Embedding weld
Figure 1 - Aspect of the different welds.
T4 condition T6 condition T7 condition
Figure 2 - Structure of the 8090 alloy in the three conditions :
T4 (solution treated), T6 (aged) and T7 (overaged).
200 L 0 before ageing after ageing
Base metal Butt welds Embedding welds
0 ,
Figure 3 - Tensile tests results for base metal, butt welds and embedding welds.
. @
Initial condi-
-tion of 4 T6 T 4 T 6 T 4 T 6
base metal
0 before ageing after ageing
I
I
II
II
- - -
Initial con-
-dition of T4 T 6
1 ; 14 T 6 T4 T6
base metal
C I I
