8/10/2019 WJ_1972_02_s64.pdf

1/7

Development o f Fil ler Metals

and

Procedures fo r

Vacuum

Braz ing

o f

Alum inum

S e v e r a l b r a z in g f il l e r m e t a l c o m p o s i ti o n s h a v e b e e n d e v e lo p e d

w h i c h o f f e r s i g n i f ic a n t im p r o v e m e n t s o v e r e x i s t in g c o m p o s i ti o n s

T h e y b r a z e in v a c u u m

at

t e m p e r a t u r e s l o w e r t h a n n o r m a l f l o w

t e m p e r a t u r e s a n d h a v e e q u a l o r b e t t e r f lo w a b i l i t y

B Y W. J . W E R N E R , G. M . S L A U G H T E R A N D F. B . G U R T N E R

Introduction

This report documents work per

formed toward the development of

new brazing filler metals for vacuum-

fluxless brazing (1 X

1 0 ~

6

to r r )

certain aluminum alloys of interest to

the Army. The base metals under

considerat ion were al loys 6061, 2219,

7075 and 2024. Brazing filler metal

flow temperatures needed for these

al loys encompass the temperature

range 900 to 1200F. Specifically, the

contract called for the development of

alloys with flow temperatures of 950,

1000,

and 1050F . Final ly , corrosion

compatibility of the brazing filler met

al with certain chemical agents was

necessary and to this end a survey of

potent ial ly compatible elements com

piled by the contractor was utilized.

We began the invest igat ion with a

survey of the l i terature. Unfortunate

ly, there is very little published work

on fluxless-vacuum and/or inert gas

brazing of aluminum. M. M.

Schwar tz

1

et al showed the feasibility

of vacuum fluxless brazing production

quanti t ies of aluminum al loy 6061

containers of helium leaktight quality

by closely controlling process parame

ters using a commercial brazing filler

metal . Brazing al loy No. 718 (nomi

nal ly 88% aluminum, 12% si l icon)

was used. This alloy is widely used

commercially for both dip and fur

nace brazing and is available in both

wire and foil form. As might be ex

pected, the success of the endeavor

was largely due to the use of laborato-

MESSRS. WERNER and SLAUGHTER are

with the U.S. Atomic Energ y Comm ission.

Tenn. which is operated by Union Carbide

Corp. MR. GURTNER is with the Dept.

ot the Army, Technical Support Directo

ra te .

Industrial Operations Div., Edge-

wood Arsenal , Md.

ry cleanliness levels under production

condit ions. The maximum al lowable

lag between cleaning and brazing was

found to be 12 hours.

C. S. Beuyukian

2

developed tech

niques for vacuum or inert gas fluxless

brazing of aluminum cold plates for

use in Apollo command modules . In

this work, brazing filler metal No. 718

and No. 23 brazing sheet were evalu

ated. Alloy No. 718 is nominal ly 88%

aluminum , 12 % si l icon; No .

23

b raz

ing sheet is comprised of 6951 base

alloy clad on one side with 4045

brazing filler

metalnominally

9 0 %

aluminum, 10% si l icon. Base metals

6061 and 5052 were considered for

the main body of the assembly.

In general, better results were ob

tained using vacuum. The techniques

developed are unique in that stringent

flatness requirements placed on the

assembly by design required that braz

ing operat ions be performed in heated

platen presses at moderate pressures.

The use of pressure during brazing

undoubtedly influenced oxide penetra

t ion and/or displacement during the

brazing operat ion. Product ion brazing

was carried out in the temperature

range 1055 to 1095F using brazing

times of at least 10 minutes.

Under these condit ions, aluminum

alloy 6061 was preferred over 5052

because alloy 5052 exhibited a greater

suscept ibi l i ty to in tergranular penetra

tion by silicon. Use of alloy 5052

would therefore have required more

rigid t ime- temperature control during

the brazing cycle. In addition, silicon

diffusion resulted in embrittlement of

5052.

No . 23 brazing sheet was chosen

for product ion over the combinat ion

of brazing al loy Nos. 718 and 6061

for both metallurgical and process ad

vantages. As a single entity, it was

immediately more desirable from a

cleaning, assembling and material

handling s tandpoint . Metal lurgical ly ,

the 4045 brazing filler metal with its

lower silicon content allowed greater

lat i tude in processing parameters than

did alloy No. 718.

Final ly , the workers at Aeronca,

Inc. completed a study on inert gas

brazing of aluminum in early 1967.

3

Their work was concerned with de

velopment of h igh s trength brazed

aluminum honeycomb structures

which would withstand a range of

cryogenic (423F) through elevated

(600F) temperatures . All of the base

metals involved in the s tudy, X7005,

X7106, and 7039, began to melt with

in the range of 1080 to

1120F.

As a

resul t , a 1050F maximum flow tem

perature for the brazing filler metal

was needed.

Three commercial brazing al loys

were evaluated in combinat ion with

the aforementioned base metals

716, 718, and 719. Nu mb er 716 con

ta ins nomina l ly 86 % a luminum, 10%

sil icon, and 4% copper; 718 contains

nominal ly 88% aluminum, 12% si l i

con; and 719 contains nominal ly 76%

aluminum, 10% si l icon, 10% zinc and

4 % copper. I t was found that the

aluminum-silicon brazing alloys per

formed best as claddings.

The researchers developed several

new brazing filler metals during the

course of their investigation. Two in

part icular showed promise. Both al

loys had a base composi t ion of 68%

aluminum, 7% si l icon, 15% germani

um; their compositions were modified

with 10% zinc, and 10% si lver, re

spectively. Both alloys brazed at

1020F. These new al loys looked espe

cially good in combination with

64-s ] F E B R U A R Y 1 9 7 2

8/10/2019 WJ_1972_02_s64.pdf

2/7

Table

1Nominal

Composit ions,

A l lo y d e s i g n a t i o n

6061 ( l im i t i n g )

6061 (n om i na l )

2219

1

( l i m i t i n g )

2219

2

( n o m i n a l )

7075

( li m i t i n g )

7075 ( n o m i n a l )

2024 ( l im i t i n g )

2024 ( no m i na l )

.

Si

Li

0.40-0.8

0.6

0.20

0.40

0.50

mits

and Melt ing Ra

Fe

0.7

0.30

0.50

0.50

Cu

0.15-0.40

0.27

5.8 -6.8

6.3

1.2 -2.0

1.6

3.8 -4.9

4.4

n g e s of Alloys Under Con

- C o m p o s i t i o n

M n

0.15

0.20-0.40

0.30

0.30

0.30-0.9

0.6

w e i g h t p e

M g

0.8 -1.2

1.0

0.02

2.1 -2.9

2.5

1.2

-1.8

1.5

sideration

Cr

0.04-0.35

0.20

0.18-0.35

0.30

0.10

Zn

0.25

0.10

5.1 -6 .1

5.6

0.25

T i

0.15

0.20-0.10

0.06

0.20

A p p r o x i m a t e

-,

m e l t i n g

r a n g e ,F

1080-1200

1080-1200

1010-1190

1010-1190

890-1180

890-1180

935-1180

935-1180

1

V a n a d i u m 0 . 0 5- 0. 15 , z i r c o n i u m 0 .1 0- 0. 25

-

V a n a d i u m 0 .10 , z i r c o n i u m 0.18

X 7 1 0 6 . Alloy 719 remained the num

ber one choice for brazing X7005.

M a t e r i a l s

Table 1 shows the nominal com

positions and compositional limits of

the base metals under consideration in

the program, along with their melting

ranges. Joining of alloys 6061 and

2219 is accomplished industrially by

dip or furnace brazing techniques both

of which employ liberal amounts of

flux. In addition, alloy 6061 has also

been brazed without flux using vacu

um and/or inert atmospheres .

1

*

2

A s

a result, good cleaning and handling

procedures are not a problem with

these two alloys. In fact, cleaning

procedures are available in the Metals

and Ceramics Division for both of

these alloys since they are routinely

hot roll-bonded into dispersion type

fuel plates using standard picture

frame techniques.

Alloys 7075 and 2024, on the other

hand, are not considered brazeable

using established commercial tech

niques and commercial brazing filler

alloys. In the first place, both alloys

have melting points below the flow

temperatures of the commercial braz

ing filler metals (Table 1 ) . Secondly,

both al loys contain appreciable

amounts of magnesium (2.5 and

1.5%, respect ively). Normally , al loys

with magnesium contents greater than

2 . 0 % are considered difficult to braze

industrially; and alloys with magnesium

contents greater than 2 .5% are con

sidered unbrazeable. This is due to the

fact that state-of-the-art fluxes do not

remove the tenacious oxides formed

on these alloys.

E q u i p m e n t a n d E x p e r i m e n t a l

P r o c e d u r e

The vacuum furnace apparatus for

flow temperature and wettabi l i ty de

terminations is shown in Fig. 1. The

system is capable of maintaining a

vacuum of 1 X

10 ~

r>

torr at brazing

temperature. The picture shows the

furnace rolled back off the muffle. In

a typical brazing cycle the specimen is

placed into the cold muffle. After

pump-down, the heated furnace is

rolled onto the muffle, and the work

very rapidly comes to temperature.

After holding for the proper brazing

t ime, the furnace is rolled off the

muffle. Simultaneous with the former

operat ion, hel ium can be admit ted to

facilitate rapid cooling or quenching

of the test assem bly. Diffusion effects

can probably be limited by both of

these operations.

A typical t ime- temperature re

sponse curve for the furnace is shown

in Fig . 2 ; the temperature measure

ments indicated are those of an actual

sample. Chromel-P versus alumel

thermocouples were at tached to a

specimen and temperature measure

ments were made using a potent iom-

1

' :.

';..:

\

'

* ( & -

t

i

' * ~ * i

8/10/2019 WJ_1972_02_s64.pdf

3/7

Table 2-

-List of Potentially Compatible

Metal

Alloy Formulation

Ele

m e n t

Al

A m

Sb

Ba

Be

B

Ca

Ce

Cr

Cu

D y

Er

Ge

A u

Hf

In

Ir

Fe

Li

M g

M n

M o

Nd

Ni

Nb

Os

P d

P t

P r

Re

Rh

Ru

Sm

A g

Ta

Te

Th

T i

V

Yb

Y

Zr

P o t e n t i a l ,

v o l t s

-1 .706

+0.212

- 2 . 9 0

- 2 . 7 6

-2 .335

- 0 . 4 1

+0.158

+1.42

- 0 . 4 9

+0.777

-3 .045

-2 .375

-1 .029

-2 .246

- 0 . 2 3

+0.344(?)

+0.7966

+0.593

- 2 . 0

-0 .255

Elements for Brazing Filler

Supplied by Edgewood Arsenal

M e l t i n g

po i n t , F

1220.4

1562

1166.9

1317

2460/2640

3690

1540

1495

3407

1981.4

2565

2727

1719

1945.4

4032

313.1

4449

2799

1688

357

1202

2273

4730

1866

2647

4474

4900

2826

3217

1686

5755

3571

4530

1962

1760.9

5425

842

3182

3035

3450

1515

2723

3366

B o i l i n g

p o i n t ,F

4442

2516

2980

5378

2908.6

6278

4829

4703

4226

4766

5125

5380

9750

3632

9570

5432

6276.2

2426

2025

3900

10,040

5756

4950

8901

9950

7200

8185

5468

10,650

8130

4900

2966

4010

9800

1813.6

6332

5900

6150

2786

5800

6470

S pe c i f i c

g r a v i t y

2.6989

11.7

6.691

3.5

1.848

2.34

1.55

8.23/6.67

7.18-2

8.96

8.526

9.051

5.323

19.32

13.29

7.31

22.42

7.874

5.98/5.186

0.534

1.728

7.21/7.44

10.22

6.80/7.004

8.902

8.57

22.57

12.02

21.45

6.6/6.7

21.02

12.41

12.41

7.5/7.4

10.50

16.6

6.24

11.66

4.54

6.11

6.977

4.45

6.35

S o l i d

s o l u b i l i t y /F *

0.1 /1232.6

0.05 /1166

0.00190/1190.86

2.8770/1108.8

0.61%/1166

4.10%/932

1.22%/1223.6

13 /1173.2

0.052 /1211

0.0370/1121

5.2 /

11.5 /752

1.35%/1158.8

0.040 /1157

0.1%/1139

0.1 /1215.5

0.1 /1218.2

Eu t e c t i c 28

0.1 /1173.2

1-1.5%/1220

0.6 /1224.5

0.1 /1191.2

0.28 /1220

* P e r c e n t a t t e m p ( F ) .

C O MP O S I T I O N (>%)

1

1 Z

BOO

5

4 0 0

In

/

...

tst

--.

S

F i g .

3Ternary

plo t o f t h e Al-Si-ln s y s t e m w i t h a t t a c h e d

b in a r y p ha s e d ia g r a m s fo r e s t i m a t i n g c o m p o s i t io n s o f p o t e n

t i a l i n t e r e s t t o p r o g r a m

ployed, care is taken to reduce the

oxide th ickness to a wo rkab le mini

mum before flux is applied.

The consensus on the mechanism of

flux action is as follows: First, as the

assembly is brought to brazing tem

perature the oxide film

microfissures

due to the differences in coefficients of

thermal expansion between the oxide

and base metal . Flux readi ly enters

these microfissures and undermines

the oxide to some extent. If the oxide

is

workably

thin , i t breaks up during

the undermining process . This contin

ues until the flux is consumed or the

metal surface is cleared of oxide.

In fluxless brazing, we must assume

that , as in commercial operat ions, a

workably thin oxide film is microfis-

sured during heat-up to the brazing

tempera tu re . Undermin ing o f the ox

ide in the fluxless process must be due

to the action of the brazing filler

me tal. It is note wo rthy th at diffusion

(over short d is tances) may play an

important role in the fluxless brazing

process . Rate of heat ing to brazing

temperature is also a factor of major

importance s ince oxidat ion of alumi

num takes place in the best vacuums

and/or inert atmospheres . In addit ion,

faster heating rates may affect the

degree of oxide microfissuring. In any

event, there is a multiplicity of factors

to consider which probably will affect

the vacuu m brazing of aluminu m.

Both 6061 and 2219, as well as all

the experimental brazing filler metals,

were cleaned by immersion in to a 20

vol%HN0

8

2 vol %HFwat er

solu

t ion at room temperature. The clean

ing step was followed immediately by

a cold water r inse which, in turn , was

followed by flushing with acetone. Al

loys 2024 and 7075 did not respond to

the aforementioned chemical cleaning

process to our satisfaction. Both alloys

did, however, respond to a low-

temperature perchloric acid electropol-

ishing t reatment .

In our very first experiments we

noted that test results were influenced

by the t ime span between cleaning and

brazing. As a result, we held the time

between cleaning and brazing to a

max imum of 1 hour w hich, al though

possibly somewhat difficult for pro

duct ion work, was fel t to be opt imum

for experimental brazing filler metal

evaluat ion.

Brazing Alloy

Development

Experimental brazing fi l ler metal

composi t ions were formulated using

binary phase diagram information to

est imate the behavior of ternary al

loys. A list of potentially compatible

elements compiled by the contractor

was used as a guide (Table 2) but it

was not utilized absolutely since this

would have seriously limited the choice

66-s i F E B R U A R Y 1 97 2

8/10/2019 WJ_1972_02_s64.pdf

4/7

1600

800

G60

400

A.

?=*

C O M P O S I T I O N (wl ?

2 0 4 0 6 0

^

v?

u

BO

S

- , . J :

T~

8/10/2019 WJ_1972_02_s64.pdf

5/7

F i g .

7Macro

of p a d t e s t w i t h Al-Si-ln A l lo y N o . 8 v a c u u m

b razed f o r 7 m i nu t es a t 1075F

F i g . 9 M ac r o o f p a d t e s t o n A l - S i -l n a l l o y N o . 6 v a c u u m

b r a z e d f o r 7 m i n u t e s a t 1 085F . N o t e e x c e s s i v e f i l l e r m e t a l -

ba s e m e t a l r e a c t i o n

F i g . 10T-joint braze d w i th A l -S i - ln a l l o y No. 6 a t 1085F for

5 m i n u t e s

F i g .

8Micro

of i n t e r f ac e be tween 6061

bas e m e t a l a n d N o . 8 A l - S i - ln a l l o y .

M a g :250X

Table

4

Flow

Temperatures and

Compositions of the

Al-Si-Ge

Alloys

F low

A l l o y C o m p o s i t io n , w t . t e m p ,

n u m b e r Al Si Ge F

1

2

3

4

5

6

7

8

9

10

11

12

55

55

55

55

45

45

45

45

35

35

35

35

5

10

15

20

5

10

15

20

5

10

15

20

40

35

30

25

50

45

40

35

60

55

50

45

1020

1060

1060

1065

1020

1060

1065

1095

1020

1065

1075

1075

filler metals are quite close to the

melting points of the base metals. The

same alloy was subsequently used to

braze the T-joint shown in Fig. 10

using a slightly shorter brazing cycle

with obviously much improved results.

Our experience indicates that even

further improvement is possible.

Initial attempts to fabricate this al

loy by hot swaging have met with

limited success. It may be necessary to

break down the cast structure by ex

trusion before hot swaging to wire.

Aluminum-Sil icon-Germanium System

Twelve different compositions were

formulated and tested for flow tem

per atu re and flowability-wettability in

this system. The location of these

experimental brazing filler metals on

the ternary layout is shown in Fig. 4.

Table 4 gives the flow temperatures of

these alloys along with their composi

tions. All of the formulated alloys

melted at reasonable temperatures

and flowed on the 6061 base metal

(heavi ly shaded area on the plot) .

General ly speaking, the flow tempera

tures of these alloys increased with

increasing silicon content. All of the

al loys containing 5% Si (1 , 5 , and 9)

exhibi ted flow temperatures of 1020F.

Increasing the silicon content to 20%

raised the flow temperature to as high

as 1095F. The lightly shaded area of

the layout shows those compositions

which may be of further interest.

Figure

11

shows a series of typical

pad tests made at different tempera

tures (in vacuum) with the filler met

al No. 9. Using successively lower test

temperatures , we establ ished that the

flow temperature of this alloy was

1020 F. Note the excellent flowability

and wettability of this experimental

composi t ion at al l temperatures

tested. We subsequently used this

same alloy to make the T-joint shown

in Fig. 12, in which the brazing filler

metal is preplaced at one end of the

joint and flow proceeds along the

capillary. The base metal for the T-

joint was 6061 and the braze was

performed by holding for 2.5 minutes

at 1020F. Good filleting is evident.

Figure 13 shows a macro of the

1020F pad tes t performed on al loy

68-s

i F E B R U A R Y 1 97 2

8/10/2019 WJ_1972_02_s64.pdf

6/7

N o. 5 . The 1020F b raz ing tempera

ture, 7 minute brazing t ime combina

tion appears to be slightly excessive

for this alloy since reaction completely

through the pad has taken place. Nev

ertheless, the wetting and flow ex

hibited is quite good. It should be

noted that th is brazing temperature is

lower than that used for commercial

state-of-the-art brazing filler metals

and, as such, is a significant advance

ment in aluminum brazing technol

ogy.

Fig ure 14 shows a high magnifica

tion view of the interface between

base metal and braze metal for this

part icular pad tes t . Both photos sug

gest that this composition is very near

th e Al-Si-Ge eutect ic composi t ion.

Figures 15 and 16 show the pad

test results for one of the higher melt

ing Al-Si-Ge al loys, No. 8 . This was

the highest melting of this series of

alloys. This filler metal also has excel

lent flow and wetting characteristics

and is typical of the higher melting

alloys. The degree of reaction with the

base metal is satisfactory.

All of the Al-Si-Ge alloys were

quite brittle and are not amenable to

fabrication into wire or sheet by con

ventional techniques.

Aluminum-Silicon-Yttrium System

Twenty different composi t ions were

formulated and tes ted for f low tem

pe ra tur e and flowability-wettability in

this system. The location of these

experimental brazing filler metals on

the ternary layout is shown in Fig. 5.

The l ight ly shaded area shows the

locat ion of the most promising com

positions. Table 5 gives the flow tem

peratures of the al loys that melted

below the melting point of the 6061

base metal and the compositions of all

the alloys tested.

The higher f low temperatures of

these alloys rather limit their use per

se as ternary alloys. However, one

must remember that addi t ions of mi

nor quantities of elements such as Cu,

Sn and Zn could result in considerable

flow point reduct ion.

Of the seven experimental composi

tions in this ternary system which did

melt below

1150F,

excel lent wett ing

and flow on 6061 base metal was

obtained. Alloy No. 18 (70 Al- 25 Si-

5Y)

exhibited the lowest flow temper

ature. However, as was the case for

some compositions in the other series

investigated, base metal-filler metal in

teract ion occurred rapidly and exces

s ive penetrat ion was a problem. Thus,

careful control of the time-

temperature thermal cycle (or further

alloying with additional melting point

depressants) is necessary.

The alloys in the

Al-Si-Y

system

were much more fabricable than any

of the other experimental brazing

filler metals investigated. They were

readi ly reduced to V

16

-in. wire, as

shown in Fig. 17.

Summary an d Conclusion

During the course of th is program,

we have developed several brazing

filler metal compositions that appear

to exhibit significant improvements

over exis t ing commercial composi

t ions. They braze in vacuum at tem

peratures lower than the flow temper

atures of commercial brazing al loys

and have equ al or better flowability.

F i g . 11Wetting t es t s o n A l - Si -G e N o . 9 m ad e a t s u c c e s s i v e l y h i gh e r t em pe r a t u r e s

p ro ce e d in g fr o m the le f t . (1) 1020F, (2) 1065F, (3) 1075F, (4) 1095F. Exc e l le n t we t t i n g

i s e v i d e n t o v e r t h e 75F r a n g e o f t e m p e r a t u r e s ho w n

' / '

';:::

V

:

:S

.

Jr

F i g . 14Micro

of i n t e r f ac e be tween 6061

base m e t a l an d No . 5 A l -S i-Ge a l l o y .

M a g :

250X

F i g . 12T-joint of A l -S i -Ge a l l oy No . 9 an d 6061 base m e t a l .

B r a z i n g w a s p e r f o r m ed a t 1020F fo r 2 .5 m i n u t e s . E x c e l l e n t

f l ow i s e v i d e n t

F i g . 13Macro of p a d t e s t o n A l -S i- Ge a l l o y N o . 5 v a c u u m

b ra z e d f o r 7 m i n u t e s a t 1022F . A n e x c e s s i v e r e a c t i o n o c c u r r e d

a t o n e s p o t

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 | 69 s

8/10/2019 WJ_1972_02_s64.pdf

7/7

F i g 15Macro of padt e s t on A l -Si -Ge a l l o y No. 8 v a c u u m

b r a z e d for7 m i n u t e sat1095F

F i g 17Photoof

1/16-in.

w ir e p r o d u c e d bys w a g i n gofAl-Si-Y

a l loy No. 18 f ro m ac a s t i n g .

*

* i

:

f

F i g 16Microo fin t e r f ac e be tween 6061

b a s e m e t a l and No. 8 Al-S i -Ge a l l oy.

M a g 250X

Our lowest flow temperature1020F

is

abou t 50F lower than

the

gener

al ly accepted flow temperature of the

88A1-12

Si

comm ercial al loy.

We specifically studied alloys in

three ternary systems

and

they

all

T a b l e 5 - F l o w T e m p e r a t u

Compositionsof th

A l l o y

n u m b e r

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

C o m p o s

Al

85

80

75

70

65

85

80

75

70

65

80

75

70

65

75

70

65

70

65

65

5Al-S

i t i o n ,

Si

5

5

5

5

5

10

10

10

10

10

15

15

15

15

20

20

20

25

25

30

r e s a n d

-Y Alloys

w t . %

Y

10

15

20

25

30

5

10

15

20

25

5

10

15

20

5

10

15

5

10

5

F l o w

t e m p ,

F

1120

1140

1110

1130

1140

1140

1095

flowed on aluminum alloy 6061 in

vacuum wi thou t

the use of

flux.

The

Al-Si-ln alloys exhibited flow temper

atures inthe range 1075to 1095F and

the Al-Si-Y alloys exhibited flow tem

pera tu resin therange 1095 to 1140F.

Alloys

in the

Al-Si-Ge system were

part icularly promising and exhibited

flow temperatures

of

1020

to

1095F.

Of part icular in terest

in

this system

are the 55Al-5S i-40Ge , 45Al-5Si-

5 0 G e ,

and

35Al-5Si-60G e al loys,

all

of which flowed at 1020F; these flow

tempera tu res

are

approx imate ly

50F

below those

of

comm ercial al loys.

l t should

be

emphas ized

at

this

point that wefeel that thefull pote n

tial

of

these alloys

is yet to be

rea l

ized. That is , further work isnecessary

to show that

the

op t imum compos i

tions

in

these systems have been

found. Secondly, further minor addi

tions

of

other elem ents such as Cu,

Zn

and Sn should be investigated since

they

may

result

in

further f low tem

pera tu re reduc t ions and/or wettabili-

ty-flowability improvemen ts . Also , op

t imum t ime- temperature relat ionships

for vacuum brazing with these al loys

m u s t

be

established.

References

S c h w a r t z , M. M., Gurtner, F . B., and

S h u t t , P. K., Jr. , V a c u u m (or F l u x l e s s )

B r a z i n g - G a s Q u e n c h i n g of 60 6 1 A l u m i n u m

Alloy, W E L D I N G J O U R N A L , V ol. 46, No. 5,

May 1 9 67 , pp.

423-431.

2B e u y u k i a n ,

C. S. ,

F l u x l e s s B r a z i n g

of

Ap o l lo C o ld

PlatesDevelopment

P r o d u c

t ion , W E L D I N G J O U R N A L ,

V ol. 47, No. 9,

Sep t . 1 9 68 , pp.710-719.

3 F l u x l e s s B r a z i n g M a k e s H e a d w a y ,

Iron Age 200 V o l .

67, No. 8,

A ug . 10, 1967.

Unified Theory

of

Cumulative Damage

in

Metal Fatigue

B y J u l ie n D u b u c , B u i Q uo c T ha n g , A n d r e B a z e r g u i a n d A n d r e B i r o n

A rev iew is m a d e of thed i ff e re n t c u m u l a t i v e d a m a g e t h e o r i e s a v a i l a b l e in the

l i t e r a t u r e . A newa p p r o a c h ( u n i f ie d t h e o ry ) is s u g g e st e d w h i c h can be app l ied

t o s t r e s s - c o n t ro l l e d

or

s t r a i n - c o n t ro l l e d c o n d i t i o n s ,

an d

w h i c h c o n s i d e r s

the

o rd e r

o f app l ica t ion

of

different s t ress

or

s t r a i n l e v e ls . C o m p a r i s o n

is

m a d e w i t h

a

la rge

n u m b e r

of

test resul ts using sev eral d ifferent le vels .

The

t h e o r y

is

a l so a pp l ied

to

some cases

of

r a n d o m l o a d i n g .

I t

is

fo u n d t h a t

the

p ro p o s e d t h e o ry y i e l ds

an

i m p ro v e d a g re e m e n t w i t h e x p e r i

men ta l resu l t s , espec ia l ly

for

c a s e s w h e re t h e r e

is a

la rge d i f fe rence be t we en leve l s .

Th e p r i c e

of WRC

Bulletin

162 is

$ 1 . 5 0

per

c o p y . O r d e r s

for ten or

m o r e

cop ies shou ld

be

s e n t

to the

W e l d i n g R e s e a r c h C o u n c i l ,

3 4 5 E.

4 7 t h

St., New

Y o rk , 1 0 0 1 7 . S in g l e c o p y o rd e r s s h o u l d be sen t to A W S , 2 501 N.W. 7th St.

M i a m i , F l a . 3 3 1 2 5 .

W R C

B u l l e t i n

N o

162

J u n e

1 9 7 1

70-s | F E B R U A R Y 1972