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TitleStudies on Flux Action in Silver Brazing : Behavior of Bag : 5 Filler Met

al on Stainless Steel Plate due to Flux Action

Author(s) Miyake, Masaaki; Nakagawa, Keisuke; Tsujino, Bunzo

Editor(s)

CitationBulletin of University of Osaka Prefecture. Series A, Engineering and nat

ural sciences. 1978, 27(1), p.125-135

Issue Date 1978-10-31

URL http://hdl.handle.net/10466/8307

Rights

125

Studies on Flux Action in Silver Brazing

- Behavior of BAg-5 Filler Metal on Stainless Steel Plate

due to Flux Action -

Masaaki MiyAKE*, Keisuke NAKAGAwA* and Bunzo TsuJiNo**

(Received June 15, 1978)

For silver brazing, the chloride system fluxes (experimental fiux) which provide

superior spread-ability in comparison with fluoride system fluxes (commercial fiux)

had been developed by one of the authors. In this'research, properties of both system

fluxes on silver brazing for SUS304 stainless steel were investigated at variousjoints such

as lap, tee and butt. The results obtained are summarized as follows:

(1) For lap joint, the length of penetration of BAg-5 alloy into gap is affected by

the viscotiy of flux at no gap joint and by the spread-ability of BAg-5 alloy at

small gap joint (O.lmm). , (2) For tee joint, the formation of fi11et is affected by the spread-ability of BAg-5

alloy, and superior fi11et is formed by fluxes which provide inferior spread-

ability.

(3) For butt joint, superior results are obtained by use of the commercial flux in

the face-fed brazing method and by use of the experimental flux in the pre-

placed brazing method.

1. Introduction

For the silver brazing on stainless steel in atomosphere, fluxes which have elimination

abthty for oxidation Mm have been developed. In these fluxes, fluoride system fiuxes

of Na2B407-H3B03 contained KF andlor KBF4 were mainly used!). Generally, in

brazing of actual joints using these fiuxes, superior spread-ability of silver fi11er metals

for variousjoints and those base metals was required.

Already, one ofthe authors and other co-workers developed various mixed salt fiuxes

(experimental flux: MCln/KCI-LiCl eut.). And they reported2) that when such fluxes

were used, the reaction ofBAg alloy with NiC12 etc. contained in fluxes or dissolution of

metals (Fe, Ni and Cu etc.) in fluxes into BAg alloy after reaction promoted the spread-

ability of fi11er metal on base metals such as Cu and mild steel.

In this study, eflfbct of experimental or commercial flux on silver brazability fbr

SUS304 stainless steel was estimated for tee, butt and lap joints. Namely, the penetration

of molten BAg-5 alloy into gap of lap joint, formation of fillet for tee joint and joint

strength for butt joint were estimated.

* Course of Welding Engineering, Junior College of Engineering. Katsuyama-Minami, Ikuno-ku,

Osaka, 544 Japan.** Liberal Arts, Junior College of Engineering.

126 Masaaki MIYAKE, Keisuke NAKAGAWA and Bunzo TSUJINO

2. ExperimentalApparatusandProcedures

In this test, BAg-5 as a silver filler metal and SUS304 stainless steel as a base metal

were used. Mixed salt fluxes added various 1Owt%metallic chlorides (A:FeC13, B:NiC12,

C:CuCl, D:AgCl, E:CuC12 , F:CrC13 and G:SnC12 ) to 30wt%KCI-70wt%LiCl (base flux)

were used as experimental flux. And H (base flux) and I (fluoride system flux) were used

to compare with the experimental flux.

2-1. Apparatus and experimental procedure for spread test

Figure 1 shows the apparatus used for spread test. Surface of SUS-304 stainless steel

,

Heating plate

Supporter

Base metal

AsbestosFiller metalThermocouple

plate

Nichrom

orter

,'

Fig. 1. Apparatusused for spread test ,

plate (40 × 40 × O.5mm) was polished with #600 emery paper and washed by water and

cleaned by acetone just befbre the spread test. For the spread test,BAg-5 (O.lg) and the

flux (O.2g) were carefu11y Placed on the SU304 stainless steel plate, and these were heated,

at 8000C and kept at that temperature for one minute on heating plate. After cooling,

the spread area was measured by the planimeter.

2-2.

(a).

Was

Apparatus and experimental procedure for lapjoint

As no gap specimen, two plates having no groove were combined together (see Fig. 2

And as small gap specimen, one plate having groove of 9mm wide × O.lmm depth

combined with one plate having no groove (see Fig. 2(b)). The surfaces of these

Studies on F7tix Action in Silver Brazitrg 127

BA -

Ftux

5040

l

'

II/ 9'

I

, BAg-5

Ftux

m ･･.:i. tttti 5.

no gap .Size and shape of lap joint specimen

(a) no gap specimen (gap is created by the empty-weight of specimen)

(b) smallgap specimen tgap: O.1 mm)

5040

, m---".:I･l

otp---- m

m

Fig. 2.

plates were polished with #600 emery paper. And then, after these combined plates

were fixed by Mo thin wire (O.5mm), BAg-5 (1.6¢ x 9rnm) and flux (O.25g) were placed

as shown in Fig. 2. These were heated at 8000C and kept at that temperature fbr one

minute on the heating plate. The penetration length of BAg-5 alloy was measured at five

points of exfoliated test specimen after brazing and that mean value was calculated.

2-3. Apparatusandexperimenta1procedureforteejoint

As shown in Fig. 3, BAg-5 filler metal (1.6¢ × 2.5mm, O.45g) was placed on one

corner, and the flux (O.25g) was placed on both corners. The vertical and horizontal

Ftux

-: --:- - :-:- li:--1-1-

-:-:t-- :-:----: Ftow -

Brazing fitter metat

(BAg-5)

:::::"'

--- i ---t ---- -::---- :------

Fig. 3. Illustration of brazing method for tee joint

plates were fixed by Mo thn wire without preparation ofgap. Heating condition was the

same one as mentioned in 2-2. After brazing, the test specimen was cut at aright angle

to longitudinal direction on the center part of tee joint, and then cross sectional area of

fillet, the radious curvature, the receding contact angle and the raised height of Mlet were

measured.

128 Masaaki MIYAKE, Keisuke NAKAGAWA and Bunzo TSUJINO

2-4. Apparatus and experimental procedure for buttjoint

Figure 4 and 5 show the shape of specimen in this test. For the brazing ofbutt joint,

two methods were applied. One of them was face-fed brazing method and it was

practiced by feeding of BAg-5 filler metal into the gap (O.27 mm) of butt joint coated

pt3

rn5

:t ee,:'N

100

a3 2

V.:

too

e- t

b

Fig. 4. Size and shape of buttjoint specimen

used for face-fed brazing method

Fig. 5. Size and shape of buttjoint specimens

used for pre-placed brazing method

with impaste flux. The other was pre-placed brazing method, and the ring of BAg-5

filler metal with inside dia. of 13mm arid powdery fiux were set as shown in Fig. 6;

In these methods, the joint was heated at 8ooOC for one minute by high frequency

induction heating during brazing. After brazing, these butt joint spectmens were machned

as shown in Fig. 7 or 8 and tensile test was carried out at the tension speed of2mm/sec.

-

lb¢1,3

,

Flux

Brazing fi"er metat

(BAg-5)

a¢20

,

Fig. 6. Illustration of pre-placed brazing method

Studies on rutix Action in stlver Brazirrg 129

bra2ed part

oo200

N

t---

brazed part

-- t'-'-t -- eeo- '-ee:･--16R 16R

,88

Fig. 7. Size and shape of tensile test specimen

(face-fed brazing method)

Fig. 8. Size and skape of tensile test specimen

(pre-placed brazing method)

3. Results and Discussions

3-1. Spread-ability ofBAg-5 rnler meta1 with the experimental flux on laboratory work

In order to estimate the spread-ability of BAg-5 fi11er rnetal for SUS304 stainless

steel, the efTects of the chloride system flux and the fluoride system flux on the spread-

abthty of BAg-5 were compared by the result of the spread test3). These results of the

spread test are nummarized in Fig. 9. As shown in the figure, the spread area is greatly

CNAi

E vvdi

o Lrd

vaso Laut

5

4

3

2

1

o

ABCDEFGHI Ftux

Fig. 9. Spread area ofBAg-5 alloy with experimental and commercial fluxes

affected by the sort of metal contained in the metalhc chlorides and the spread-ability

of BAg alloy with experimental flux (A, B and C) is superior in comparison with that of

BAg alloy with the fluoride system flux (I). In the following section, silver brazing ability

for various joints using these fluxes are estimated.

130 Masaaki MIYAKE, Keisuke NAKAGrwA and Bunzo TSUJINO

3-2. Effbct of fiux on penetration of BAg alloy into lap joint

The length of penetration of BAg-5 alloy into the gap created by the empty-weight

of specimen of lap joint (see Fig. 2 (a)) is shown in Fig. 10. BAg-5 alloy with flux H

AEEv 50`

･･-･940s 30

l,is,

ABC DEFGHIFtux

Fig. 10. Effect of flux composition on penetration length of BAg-5

alloy in lap joint with no gap

didn't flow, but BAg-5 alloy with experimental fluxes A "- G flowed to the extent oflap

length (4cm) and was in saturation. Namely, the difference in penetration lengths of

BAg-5 alloy with the experimental fluxes was not observed. But the fiow of BAg-5

alloy with commercial flux (I) didn't saturate to the lap length and the penetration length

was inferior to those with the experimental fluxes. Accordngly, in such no gap joint,

the flow of BAg-5 adoy may be controned by the penetration-abihty of flux. The test

result of the lap joint with smal1 gap (O.1 mm) is shown in Fig. 11. From the figure, it

t AEEv 30S9e 2o.5

g lo2di o

----------------d------ -----

Fig. 11.

ABCDEFGH1 FluxEffect of flux composition on penetration length of BAg-5

alloy in lap joint with small gap

Studies on jFTIux Aetion in Silver Brazing 131

may be seen that the difference in penetration lengths shows the same tendency as that in

the spread areas shown in Fig. 9.

On the assumption that the liquid existed in gap of two 1imitless parallel plates fiows

as laminar fiow and its meniscus is one part of circle, the penetration length is given by

equation fbllowing4) :

al . cos e ･t･D (1) X == 3pt ,

where

X= penetration length, ai == interfacial tension,

u = viscosity(fi11ermetal+flux), e = contact angle,

D= gap of plates, t= time.The viscosities of both fluoride and chloride system fluxes at 8ooOC is shown in Table 1 .5)

The viscosity of fluoride system fiux is about 100 times of that of chloride system flux.

Table 1. Viscosity of fluxes

Flux

Chloride flux

Fluoride flux

Viscosity (c. poise)

1.3

140.0

The viscosity of mo!ten BAg-5 alloy is about 4 N 5c. poise. Accordmgly, on the assump-

tion that the penetration length is only affected by the viscosity of flux, the penetration

length of BAg-5 alloy with the fiuoride system flux (I) may become to about 1/1O of that

with the chloride system flux (A "- G) by equation (1). But this value comparatively

differed from the result shown in Fig. 11. Therefore, penetration length may be also

affected by oi･cose(wetting).

3-3. Effect of flux on rnlet formation in teejoint

By the experlmental procedure as mentioned in the section 2-3 for the teejoint, the

sound Mlet was formed at both sides of the tee joint by the penetration ofBAg-5 alloy

from one side. The variety of fillet shape caused by various fluxes was observed. Photo-

graph 1. shows the appearance of the tee joint. The cross sectional area, the receding

contact angle, the raised height and the radious curvature of fillet for tee joint are

summarized in Table 2. Figure 12 showns the relation betwee'n cross sectional area of

fillet and spread area obtained in the spread test. The cross sectional area of Mlet

becomes small with use of fiuxes which provide increase of spread area. Because quantity

of flow of BAg-5 alloy for SUS304 is increased by use of such fluxes. We calculated

the apparent interfacial tension of flux6) from the shape of fillet. Figure 13 shows

that the apparent interfacial tension becomes small with use of flux which provide

132 Masaaki MIYAKE, Keisuke NAKAGAWA and Bunzo TSUJINO

Photo. 1. Appearance ofbrazed teejoint

Table 2. Receding contact angle, cross sectional area, raised height, radious

curvature and apparent interfacial tension at fi11et of brazed teejoint

Flux

Recedingcontactangle

(degree)

Cross-sectional

areaoffillet

(Mm2)

Raisedheight

(mm)

Radiousofcurvature

(Meanvalue)(mm)

Apparentinterfacial.tenslon

o,(dyne!cm)

A 10wt%FeCl, 7.0 O.32 1.0 L13 18.15

B 10wt9.NiCl, 5.5 O.44 1.5 O.71 17.55

C 10wt9oCuCl 6.5 O.73 1.6 1.44 22.80

D 10wt9(oAgCl 3.8 O.62 1.7 129 21.05

E 10wt9bCuCl, 3.3 O.73 1.7 1.68 26.05

F 10wt9oCrCl, 8.0 O.92 1.8 1.73 32.05

G 10wt9oSnCl, 5.5 O.85 2.5 2.02 30.60

I Commercialfiux 7.8 O.78 1.5

ptA

e"E

2E..o.-v

8?:.$:･-

8-s

10

05

o

o"g F- -D.- -" 'oi 6E-- ge"--'--

BoA o

1 2 3 4Spread area(cm2)Fig. 12. Relation between cross sectional area of fillet of brazed tee

joint and spread area

Studies on Fltux Action in Silver Braziirg 133

"di' AE 40/r/N/..3o

.E v v 20E 8:a/T･'8

95

Do

Eo c

o ge

1 2 3 4Spread area (cm2)

Fig. 13. Relation between apparent interfacia1 tension and spread area

increase of spread are. And the superior shape of fiilet was not observed by use of fluxes

(A, B, C and E) which provide 1arger spread area. Reversely,the superior and ideal shape

of fillet was observed by use of fiuxes (G and H) which provide smaller spread area.

From above mentioned result, we may conclude that the use of fluxes having bad

wettabMty is better for the shape of fillet.

3-4. Effect of fiux on brazabMty of BAg-5 filler metal in butt joint

For butt joint, the flow direction of both BAg-5 alloy and flux were differed by the

brazing methods (face-fed brazing and pre-placed brazing methods). 'Iherefore it is antici-

pated that the charactor ofjoint part greatly changes by the physico-chemical properties

of fiux which are affbcted' by the flow direction of fiuex. Tables 3 and 4 show the

tensle test results ofjoint obtained by the two brazingmethods. From these tables and

Fig. 9, it is clarified that joint strength has no connection with spread-abMty of BAg-5

alloy changed by fluxes and is controlled by the defects existed in the joint which is

caused by low viscosity of fiuxes. When commercial flux was used in the face-fed

brazing method, largerjoint strength than that obtained by the use of experimental flux

was obtained due to the difference ofviscosity as shown in Table 1. But in the pre-placed

brazing method, the joint strength obtained by use of commercial flux was not so large in

comparison with that obtained by use of the experirnental fiux because many defects

existed in the joint as shown in Table 4. The small joint strength (28.2 and 29.5

kg/mm2) by fiux F were obtained in spite of low ratio of defects, which was due to the

effect of Sn dissolved into BAg-5 adoy from the fiux(SnC12). In the brazing of BAg-5

filler metal, better joint was obtained by use of fluoride system flux in face-fed brazing

method and comparativly good joint with low ratio of defect was obtained by use of

chloride system flux in pre-placed brazing method. From the above mentioned results,

we may conclude that strength of butt joint is affected by both the viscoslty ofmolten

134 Masaaki MIYAKE, Keisuke NAKAGA]VVA and Bunzo TSUJINO

Table 3. Tensile test results of SUS304 stainless steel rod brazed with

BAg-5 filler metal by face-fed brazing method

Flux Jointthickness(mm) Ultimatetensilestrength(kg/mm2)

AO.024 1.1

10wt9oFeCl,O.020 1.1

O.030 oB 10wt%NiCl,

O.024 o

O.020 7.7C 10wYoCuCl

O.021 27.7

O.O14 15.0D 10wt9oAgCl

O.022 33.3

O.O12 15.5E 10wt9.CuCl,

O.O14 6.1

FO.O13 o

10wt9oCrCl,O.O14 o

O.023 5.5G 10wt9eSnC12

O.021 21.1

IO.O14 41.6

Commercialfiux

"O.O13 51.6

Table 4. Tensile test results of SUS304 stainless siteel rod brazed with

BAg-5 filler metal by pre-placed brazing method

Flux Jointthickness(mm)Ultimatetensile

strengtli(kg/mm2) Rateofdefect(9e)

O.020 48.0 8A 10wt%FeCl,

O.O18 36.3 15

BO.030 26.7 23

10wV,NiCl,O.026 34.2 16

10wt9bCuClO.020 33.9 25

CO.020 48.2 7

O.O16 29.2 23D 10wt%AgCl

O.030 35.6 24

EO.OIO 19.3 40

10wt9eCuCl,O.OIO 20.7 14

O.O15 -28.2 18F 10wt9oSnC12

O.O13 29.5 16

O.020 46.9 15G 10wVbCrCl,

O.020 2o.e 18

O.020 28.0 45I Commericalflux

O.O13 27.5 45

Studies on Elux Action in Silver Brazing 135

flux and silver brazing method without regard to spread-ability of BAg-5 alloy.

4. Conclusion

ln this study, effbcts of fluxes on penetrationebmaty, brazabMty and joint strength

were estimated for the brazed !ap, tee and butt joints in SUS304 stainless steel by use of

the experimental and commercial fiuxes.

The results obtained are summarized as follows:

(1) For lap joint, the penetration length of BAg-5 alloy is greatly affected by the

viscosity of flux at no gap joint and also that is affected by the spread-abMty of

BAg-5 alloy at srriall gapjoint (O.1 mm gap).

(2) For tee joint, both cross sectional area of fillet and apparent interfacial tension

decrease with increasing of the spread area obtained in the spread test. Ehe

formation of fillet is affected by the spread-ability of BAg-5 alloy and superior

fillet is formed by fluxes which provide inferior spread-ability.

(3) For butt joint, especially, the strength of joint is affbcted by both the viscosity

of flux and the fiow direction of BAg-5 aboy. Superiorjoint is obtained by use

of the fluxes with low viscosity in pre-placed brazing method and also by use of

the fiuxes with high viscosity in face-fed brazing method.

.Acknowledgments

The authors wish to express their appreciation to Dr. Ohrnori and members of

Welding Research Institute of Osaka University for helpfu1 discussions. Furhter, the

authors are also gratefu1 to Dr. Okamoto, Welding Research Institute of Osaka University,

for his advices during the course of this study.

1)2)3)4)

5)

6)

References

E. A. Fenton, Brazing Manual, A. W. S., (1962).

I. Okamoto, A. Ohmori and M. Miyake, Trans. JWRI, 4, 2 (1975), 119.

I. Okamoto et aL, Preprinting of the National Meeting of J. W. S., 17 (1975), 284.

D. R. Milner, British Welding J., 5, 3 (1958), 90-104.

G. M. A. Blanc, J. Colbus and C. G. Keel, Welding J., 40, 5 (1961), 210s.

G. L. J. Bailey and H. C. Watkins, J. Inst. Metals, 80, 2 (1951), 57.