principles of brazing and soldering - technical...

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Joining Technology

Principles of Brazing and Soldering

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02490_BR_BT_Grundlage_Loeten_EN_MON4_210x279 25.10.13 20:14 Seite 1

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Page 4 1. Introduction

Page 6 2. Metallurgical and Physico-Technical Basics

Page 10 3. Wetting and Diffusion

Page 12 4. Brazing Techniques

Page 15 5. Filler Metal

Page 16 6. Fluxes

Page 19 7. Solderability of Components

Page 20 8. Annex

Page 22 9. Glossary

Principles of Brazing and SolderingJoining Technology

By Daniel SchneeUmicore AG & Co. KGBusiness Unit Technical MaterialsBusiness Line BrazeTec


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1. IntroductionIn joining technology, we differentiate betweennon-positive and material bonding connections.Non-positive connections are made by rivets or bolts, while gluing, welding, brazing and soft soldering are typical material-bonded connections – see figure 1.

Figure 1 | Types of joints

Rvite, screw Braze metal

Stress distribution in non-positive connection

Stress distribution in material bonding connection


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Brazing is a thermal process for material-bonding and separable joining and coating ofmaterials, in the course of which a liquidphase is created by melting a filler metal(also called brazing alloy) in a fusion brazingprocess (fusion brazing) or by diffusion at theinterfaces (diffusion brazing). The solidustemperature of the parent materials is notreached [1].

As a consequence, filler metals must haveseveral essential characteristics:

the melting temperature must be lowerthan that of the parent materials

parent materials must have good wettingproperties

a high degree of stability and tenacity

To be able to better understand these charac-teristics, it is essential to be aware of the

physical and metallographic basics not onlyfor the development of new filler metals butalso for effective application of the large va-riety of fillers already in use.

To learn more about the technical termsused, please refer to the annexed glossary.

1.1 Differentiation Between Welding And BrazingIn welding, materials of the same type maybe bonded with each other, e.g. steel withsteel or aluminium with aluminium. Theweld metal has a similar composition as theparent material and is thus specific to thematerial.

In brazing and soft soldering, however, ma-terials of the same type and also dissimilarmetals may be bonded to each other, e.g.steel with copper or copper with brass. The

filler metal i.e. brazing alloy is usually notspecific to the parent material. Compositionof filler materials may differ significantlyfrom that of the parent materials – see figure 2.

Distinction is made between

soft soldering with filler metals having aliquidus temperature under 450 °C.

brazing with filler metals which have aliquidus temperature above 450 °C.

high-temperature brazing in a vacuum orprotective atmosphere with filler metalshaving a liquidus temperature above 900 °C.

Figure 2 | Schematic comparison of temperatures of welding and brazing

parent material and filler metal have

almost identical melting temperatures

Udifferent materials filler metal melts prior

to parent materials

Tem

pera

ture

G1 G1 G1 G2L

TG1TG1 TZ TG1 TG2TL

Z

Tem

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Welding Brazing


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2. Metallurgical andPhysico-Technical BasicsIn describing the metal filler characteristics stated inthe introduction, one will frequently encounter technical terms such as liquidus temperature, solidustemperature, metal filler formation, eutectic alloys,diffusion zone, etc.For a better understanding of the technical basics, we have to mention a few theoretical fundamentals.

Figure 3 | Metal crystal lattice with copper and nickelatoms


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2.1 Phase DiagramsTo be able to properly assess and apply fillermetals, it is absolutely essential to be familiarwith the melting characteristics of the particularmetal or alloy. Only few pure metals (e.g. Cu)are used as a brazing filler metal. Usually mix-tures of two or more metals are used, called al-loys.

The measured data obtained from heating orcooling curves is used for compiling so-calledphase diagrams. For alloys composed of twometals, these are called binary phase diagrams.The upper curve is known as the liquidus line(L); the temperature it displays is the liquidustemperature. The lower curve showing thesolidus temperature is named the solidus line(S) - see figure 4.

Above the liquidus line, the entire alloy ismolten and liquid; below the solidus line, the

alloy is entirely solid. In the cigar-shaped zone,alloys have both solid and liquid phases and theoverall consistency accordingly is pasty. Thiszone is called the melting range or with fallingtemperatures the solidification range.

Figure 4 shows the binary phase diagram forthe two metals copper (Cu) and nickel (Ni).Both metals are entirely miscible throughoutthe entire concentration range; a feature dis-played by only a small number of systems e.g.silver-gold, copper-zinc (up to 45 wt% zinc).

The binary phase diagram shows that alloying asecond metal either changes the melting pointor establishes a melting range. Adding copperlowers the melting point of nickel, for example.

Metals have a regular structure, in which theatoms are arranged in a metal crystal lattice –see figure 3. In alloys, the metal crystal latticeis composed of the atoms of the alloying com-

Figure 4 | Copper-nickel diagram [2]

Tem

pera

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[°C

]

wt% – Nickel (Ni) Nickel (Ni)Copper (Cu)

Liquid

α-Mixed crystals

1500

1400

1300

1200

1100

1000

L

1085 °C

1455 °C

S

0 20 40 60 80 100

ponents. If the atoms of the metals of an alloyhave a similar size, such as copper and nickel,the integration of foreign atoms is not a prob-lem and the metals are absolutely miscible.

The integration of very large atoms instead of


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the original atoms is possible only to a limitedextent, which is known as partial solubility. Thisphenomenon frequently leads to changes instrength and melting ranges as well as lowermelting temperatures. In systems featuring lim-ited solubility of metals into each other, thereare frequently melting temperature minimums(eutectic points) as displayed in figure 5 for thecopper-silver system.

With a copper share of 28 weigth-%, themolten mass solidifies at 780 °C and reacts likea pure metal during solidification. In other con-centrations, the liquidus temperature rises con-sistently up to the melting point of the puremetal.

2.2 Filler Metal Melting RangeThe extent of a filler metal's melting range is de-termined by the difference between the liquidusand solidus temperatures.

The melting range is decisive in choosing a fillermetal for brazing and also influences the timeneeded for heating and the brazing period [3].

Only filler metals with a narrow melting rangeshould be selected for furnace brazing. Wideranges could lead to the formation of segrega-tion zones. As soon as the solidus temperatureis reached, the filler metal begins to melt. Thispartially liquefied material consists of the fillermetal alloy components with low meltingpoints. They wet the parent material and flowinto the brazing gap. The remainder of the alloy

component with higher melting points has anaggregate state different from that of the initialliquefied mass and remains in a non-moltenstate at the application spot. For alloys with nar-row melting ranges, the beginning and end ofliquefying of the filler metal lie close to eachother, which prevents the formation of thesematerial residues.

Filler metals with wide melting ranges are pre-dominantly used for manual brazing processesand allow filling of wider brazing gaps.

2.3 Brazing Filler Metals With LowMelting PointsLow melting temperatures or low meltingranges are significant features of any fillermetal, because these lead to low brazing tem-

Figure 5 | Binary phase diagram: silver / copper [2]

Tem

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wt% Copper (Cu) Copper (Cu)Silver (Ag)

Liquid

α + β

α β

Liquid + αLiquid + β

1200

1000

800

600

400

200

962 °C

780 °C

1085 °C

0 20 40 60 80 100

eutectic point


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peratures.

Next to silver, another metal capable of reduc-ing the melting temperature of copper is zinc(Zn). To prevent the filler metal alloy and thusthe brazing joint from embrittlement, the zinccontent of these brass alloys should not exceed45 wt%. Other metals with low melting pointslead to embrittlement (e.g. cadmium, tin, alu-minium and Magnesium) or cause thermal em-brittlement (e.g. lead, bismuth and antimonyof the filler metals and brazing joints).

The precious metals gold (Au) and silver (Ag)lower the brazing temperature of the Cu-Zn al-loys without embrittling these. The morefavourably-priced silver has even better effectsthan gold. The lower curve in figure 6 demon-strates that 10 wt% silver is more effective than

45 wt% zinc (solidus temperature is lowered byapproximately 250 to 300 °C) and that this ef-fect is consistent at all zinc contents up to 30wt% (lower curve is parallel to upper curve).

Figure 7 shows the malleability of a silver-freebrass brazing alloy with a liquidus temperatureof approx. 800 °C in comparison with the silverbrazing alloy BrazeTec 1204 (12 wt% Ag; liq-uidus temperature 830 °C). Two steel rods arebutt-jointed with one of the two filler metals re-spectively. While the joint brazed with BrazeTec1204 can be bent without failing, the silver-freejoint fractures and breaks after being bent byonly 0.5° [4].

The composition of the major components ofthe low-melting BrazeTec brazing alloys – silver,copper, and zinc – is selected to assure out-

standing processing capacities - low brazingtemperature, easy flow, high stability. The ratioof the filler metal components to each other isheld constant within relatively tight tolerances.

Brazing filler metals for particular applicationscontain more components to improve wettingof the parent materials. Filler metals with nickeland manganese additions are used for carbidetools. Their ratio of components is designated toassure maximum processing characteristicswithout greatly influencing other brazing fea-tures.

Figure 6 | Reduction of solidus temperature – a) with Zn alone, b) with Zn + 10 wt% Ag

Solid

usem

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[°C]

wt% Zinc (Zn) Zinc (Zn)Copper (Cu)

without Ag

reduced malleabilitiy

10 % Ag

1200

1100

1000

900

800

700

6000 10 20 30 40 50

Figure 7| Steel rods brazed at about 830 °C.Top: with silver-free brass brazing alloy*), the brazed jointis not ductile; Below: with BrazeTec 1204, the brazed joint is ductile.

*) Brass brazing alloys with such low brazing temperaturesare not suited for technical applications due to their brittle-ness and are therefore not produced on an industrial scale.This filler metal was manufactured particularly for this test.


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3. Wetting and Diffusion

Figure 8 | Wetting angles

Wetting angle α < 90° Wetting angle α = 90° Wetting angle α > 90°

α α α

Drop of filler metal

Parent material

Filler metals will effectively wet the parent material only ifthree essential requirements have been met:

The surfaces to be brazed and the filler metal have to bemetallically clean.

The surfaces to be brazed and the filler metal have to reachat least the working temperature.

At least one filler metal element has to be able to alloy withthe parent material.


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3.1 WettingNext to low brazing temperatures, anothercriterion to be looked into is the ability of thefiller metal to wet the parent material.

A drop of liquid filler metal touching a solidmetal surface will wet this surface and willspread to a certain degree [5]. Preconditionsfor this wetting and expanding are a cleanand oxide free metal surface, sufficient heat-ing of the filler metal and parent material,and low-viscous capacities of the moltenfiller metal.

The wetting angle α is a measurable variablefor wetting abilities and designates the anglemeasured between a drop of filler metal andthe level parent material surface – see figure 8.

With α = <90°, the parent material is wet-ted. Optimal wetting angles are at <30°.With α = 0°, wetting is total, i.e. the dropof filler metal extends over the metal sur-face in form of a thin film.

With α = 90°, the drop of filler metal haswetted the surface, but it has not spread.

With α >90°, there is no wetting.

3.2 DiffusionIn a successful brazing process, the brazingfiller metal partially alloys with a thin layer

of the parent material surface. The migrationof metal atoms essential for this process iscalled diffusion. Accordingly, the developingtransformation zones are also called diffusionzones - see figure 9. Filler metal compo-nents are found in the parent material (DP);constituents of the parent material can bedetected in the filler metal layer (DF) [6].

The consistency of brazed joints is basedupon the formation of a diffusion zone. Toprovide for formation of these zones, theatoms of the brazing alloy must be inte-grated into the metal atom structure of theparent material. Of course not all metalatoms feature identical abilities to fulfil theserequirements on solid solution formation.The larger the differences in atomic radii, thesmaller the number of atoms to be inte-grated and possibly the slower their ability tomove. In order to achieve optimal consis-tency, the filler metal should have a liquidphase of at least 5 to 10 seconds to assureformation of an adequately deep diffusionzone.

Filler metals should therefore always containa metal which is also a component partand/or alloying element of the parent mate-rial at issue. The alloying element zinc, forexample, meets this requirement very wellfor all steels and in nickel and copper basedalloys.

3.3 Changes of MicrostructureBrazed joints have a zonal structure. Next tothe unaffected parent material (P) is a ther-mal influence zone (PI), in which the parentmaterial microstructure changes due to crys-tal regeneration, recrystallization, tempering,precipitation processes or transformation ofthe crystal structure, etc. [7]. The alloy layerD is the transformation zone between theparent material and filler metal and consistsof the diffusion zones DF and DP (see 3.2.).In brazing, this layer can be so thin that it isalmost undetectable under the microscope.Next is the zone of pure filler metal F – seefigure 10.

Not all of these zones must always be pres-ent. Formation of the heat affected zone de-pends upon the brazing temperature andtime. The zone of pure filler metal may dis-appear entirely, in particular if there are nar-row brazing gaps and favourable diffusionconditions (high brazing temperature, longbrazing period).

Figure 9 | Successful brazing with defined diffusion zones Figure 10 | Structural arrangement in brazed joints

F: Filler metalDF: Diffusion zone in filler metal – surplus in brazing alloy elementsDP: Diffusion zone in parent materialP: Parent material

P: Parent material PH: Thermal influence zone in parent material F: Filler metalDF: Diffusion zone in filler metalDP: Diffusionszone in parent material

F

FDF DFDP DPPH PHP P

P P

DF

DP

P


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4. Brazing Techniques

Figure 12 | Flow of filler metal during gap brazing

Initial State Start of wetting Intermediary state Final state

Brazing filler metal

Parent material

0,1 mm

In brazing technology there are many possibilities tocategorise brazing technology like liquidus tempera-ture of filler metal, method of filler metal applicationor heating technique. In this chapter the techniqueswere classified by form of braze joint.


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4.1 Braze WeldingBraze welding is a brazing technique in whichthe surfaces to be joined to each other have agap of more than 0.5 mm. Owing to this largedistance, the strength of the applied filler met-als should be higher than that of the parentmaterial in order to warrant for sufficientstrength of the brazed joint [8]. The liquidustemperature of the filler metal may not be sig-nificantly exceeded in order to prevent thefiller metal from seeping out of the joint.

The seam preparation and working techniquefor braze welding are the same as for gaswelding.

This technique is primarily used for joining gal-vanized steel pipes – see figure 11.

4.2 Gap BrazingIn gap brazing, the workpieces are treated and

prepared so the joints form narrow capillarygaps. They are uniformly heated to brazingtemperature across the entire length of thegap. The liquid filler metal is forced into thegap by the capillary attraction – see figure 12.The majority of all brazing operations are car-ried out by gap brazing.

If the joint has been brazed in an open atmos-phere using a flux, the filler metal penetratinginto the gap has to be able to displace the fluxfrom the gap.

In gap brazing, the liquidus temperature of thefiller metal may be exceeded by 20 to 50 °C inorder to assure uniform filling of the gap.

4.2.1 Capillary Attractionnarrower the joint gap is, the greater the capil-lary attraction will be.

With a parallel gap of 0.1 mm, the capillary

pressure is at approx. 100 mbar (10 kPa). Thiscorresponds to a filler metal rise height of 10cm (filler metal density = 10 g/cm3) – see fig-ure 13. The calculated rise heights have beenconfirmed in practical tests [9].

The correct dimensioning of joint gaps (gapwidth) and cleanliness of the brazing surfacesare crucial factors for determining the capillaryattraction [10]. Excessively large gaps and im-properly cleaned surfaces reduce the capillarypressure and lead to brazing gaps being onlypartially filled.

The high capillary pressure in gaps smallerthan 0.05 mm is exploited for brazing opera-tions in protective gas atmospheres or vac-uum. For mechanized brazing with fluxes, thegap range is between 0.05 to 0.2 mm. Up to agap size of 0.2 mm, the capillary attraction issufficient to assure adequate penetration andfilling of the gap with filler metal. Wider gaps

Figure 13 | Capillary pressure dependent on gap width

Capp

illar

y pr

essu

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mba

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Gap witdh [mm]

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Figure 11 | Galvanized steel pipes braze welded with BrazeTec 60/40


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Figure 14 | Gap width for various brazing techniques

Gap width [mm]

0 0,05 0,10 0,15 0,20 0,30 0,40 0,50

Vacuum Brazing

Brazing with inert gas

Brazing with flux,automated

Brazing with flux, manual

Brazing with flux, manual

Gap Brazing

Braze Welding

figure 15 | Capillary pressure dependent on gap geometry

Capi

llary

pre

ssur

e [m

bar]

0

100

200

300

400

500

are difficult to fill and are therefore not suitedfor mechanized brazing. The range up to 0.5mm is still suited for manual brazing [11]. Forgap widths exceeding 0.5 mm, the low levelof capillary pressure prevents reliable and uni-form filling of brazing gaps with filler metal.

The minimum size for brazing with flux is aconsequence of the need to pull sufficient fluxinto the gap in order to eliminate any oxidesstill deposited on the surfaces.

The gap width ranges for various brazing tech-niques are displayed in figure 14.

In addition to the size of the gap, also the gapgeometry has a significant impact on the capil-lary attraction and thus also on the brazing re-sults. The capillary pressure in the fillet is 4.5times higher than that registered for a regularparallel gap between flat surfaces – see fig-ure 15.

4.3 Surface BrazingSurface brazing is not aimed at joining parts byway of brazing with filler metal, instead thefiller metal and optional additives are appliedto the parent material surfaces to increasehardness and as protection against wear andcorrosion.

With the BrazeCoat® technique [12], the sur-faces of component parts subject to high stressare protected against wear and tear by apply-ing a hard material / brazing web which isthen melted in a furnace process. The appliedlayers are compact, smooth and have almostno pores and are used to protect ventilator fanblades, mill housings, heavy-duty transportpumps as well as cylinders, pistons, and pistonrods in hydraulics and pneumatics engineer-ing.


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5. Filler MetalDIN ISO 857-2 defines filler metals witha liquidus temperature of under 450°Cas soft solders and over 450 °C as braz-ing filler metals.

The brazing/soldering ranges are determinedat the lower end by the melting range and atthe upper end by:

the flux (which becomes saturated with ox-ides if the temperature is too high or issubjected to an extended heating period)

the filler metal (some alloy componentsmay evaporate)

economical considerations (unnecessarilyhigh temperatures waste valuable time andenergy)

the parent material (structural changes;loss in stability)

5.1 5.1Soft Solders Solders are listed in DIN EN ISO 9453 and aredistinguished as lead containing and lead-freealloys [13].

DThe lead containing solder alloys (tin/lead,lead/tin, tin/lead/antimony, tin/lead/bis-

muth, tin/lead/cadmium, tin/lead/copper,tin/lead/silver and lead/silver) have a melt-ing range from 145 to 370 °C.

The lead-free solder alloys (tin/antimonytin/bismuth, tin/copper, tin/indium, tin/silverand more complex compositions) have a melt-ing range from 118 to 380 °C.

Lead is considered to be carcinogenic and isconsequently no longer used as a solder in nu-merous industry sectors, in particular in utilitiesplumbing and in the electronics industry.

5.2 Brazing Filler MetalsBrazing filler metals are defined in DIN EN ISO17672, where they are categorized in sevengroups according to their major alloy element– see figure 16 [14].

In addition to standardized brazing alloys,other alloy groups are also known in industrialmanufacturing processes:

CuPSnNi alloys with a melting range from 590to 620 °C for brazing copper-brass coolers inthe so-called “CuproBraze® process” [15].

Active brazing alloys – have a silver/titaniumbasis with the addition of copper and indiumfor the brazing of ceramic materials at temper-atures between 850 and 1050 °C [16].

Copper-manganese-cobalt alloy with a meltingrange between 970 and 990 °C are used forbrazing cemented carbides on steel parts inprotective gas atmospheres.

Since December 2011, the use and marketingof cadmium containing brazing filler metals inthe EU is no longer permitted. These alloyscould only be used in defence and aerospaceapplications or for safety reasons [17].

Figure 16 | Melting temperature range of filler metal groups acc. to DIN EN ISO 17672

Melting temperature [°C]

1.0501.000450 500 550 600 650 700 750 800 850 900 950 1.100 1.150 1.200

Aluminium and Magnesium Filler Metals

Silver Filler Metals

Copper-Phosphorus Filler Metals

Copper Filler Metals

Nickel and Cobalt Filler Metals

Palladium Filler Metals

Gold Filler Metals


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Flux wets metal oxides, dissolves these, andeliminates them from the metal surface. It alsoprotects the metal surface against the effectsof oxygen, and has to be entirely removablefrom the metal surface when the melted fillermetal has reached it’s brazing temperature.The flux can do all this only if

its melting temperature is at least 50 °Clower than of the applied filler metal and isalso fully effective at this temperature, and

it forms a compact uniform layer which re-mains in effect at the required brazing tem-perature and throughout the brazingperiod.

The effective temperature ranges of thesefluxes have to be inline with the brazing tem-peratures of the applied filler metal. There is arough distinction between fluxes for soft sol-dering and fluxes for brazing. Within these twocategories, there are further temperatureranges which have to be coordinated with thefiller metals used [18].

In addition, the fluxes must match the differ-ing chemical conditions of the oxides to be dis-solved. As a consequence, there is no universalflux [19].

6. FluxesAccording to DIN ISO 857-2, a fluxis a non-metal material which ispredominantly designated to remove oxides on the surfaces to be brazed and to prevent renewed oxide formation.

Type Based on Working temperature Application Residues

FH10 Boron compounds, fluorides 550 °C – 800 °C General purpose fluxes Corrosive

FH11 Boron compounds, fluorides, chlorides 550 °C – 800 °C Copper-aluminium alloys Corrosive

FH12 Boron compounds, fluorides, boron 550 °C – 850 °C Stainless and other alloy steels and hard metals Corrosive

FH20 Boron compounds 700 °C – 1000 °C General purpose fluxes Corrosive

FH21 Boron compounds 750 °C – 1100 °C General purpose fluxes Non-corrosive

FH30 Boron & silicon compounds, phosphates >1000 °C Copper and nickel brazing filler metals Non-corrosive

FH40 Chloride, fluorides, boron free 600 – 1000 °C Boron free applications Corrosive

FL10 Chlorides, fluorides, lithium compounds > 550 °C Light metals Corrosive

FL20 Fluorides > 550 °C Light metals Non-corrosive

Table 1 | Brazing fluxes according DIN EN 1045


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6.1 Soldering FluxesFluxes for soft soldering are listed in the DINEN 29454-1 standard [20].

To explain how soft soldering fluxes work,here is an example with copper and the hy-drous flux type 3.1.2 A (see table 3) with zincchloride. Adding thermal energy leads to thefollowing reaction:

ZnCl2 + H2O Zn(OH)Cl + HCl

The nascent hydrochloric acid reduces the cop-per oxide at the component surface to copperchloride. This is soluble in water and can easilybe removed from the surface.

CuO + 2 HCl CuCl2 + H2O

6.2 Brazing FluxesFluxes for brazing are stated in the DIN EN1045 standard [21]. Excerpts from this stan-dard stating the essential flux types with fluxbasis materials are listed in the table 1.

The fluxes' soluble capacities are not identicalfor all metal oxides. For the flux BrazeTec h,the soluble capacities for the most frequentheavy metal oxides were measured at varioustemperatures. At a temperature range of be-

tween 650 to 750 °C, it can dissolve betweenapproximately 1 (Cr2O3) to 5 (ZnO) percent inweight of metal oxide. If the flux is saturatedwith metal oxide, it loses its effectiveness. Asa consequence, the brazing period is limitedwhen brazing with flux in air.

This also means that an appropriately largeamount of molten flux must be available toeliminate the oxides, as in the other case thebrazing process will be faulty. Extremely nar-row gaps, e.g. less than 0.05 mm, might causedifficulties because there may not be an ade-quate amount of flux in the gap. This of coursehas a major impact on constructional design asrelates to brazing capacities.

A flux may not be expected to have a servicelife of more than 5 minutes; real-life applica-tions usually have a much shorter service life.

In many instances, the flux will turn black,which clearly indicates that it is saturated – seefigure 17. If brazing has not yet been com-pleted to this point of time, the work phasewill have to be aborted. Addition of fresh un-spent flux is now also no longer possible. Toachieve a flawless brazed joint, the followingsteps must be taken: the component must cooloff and be cleaned. New flux must be applied,

Flux

Atmospheric oxygen

Oxygen, Oxide

Oxide

Parent material

Flux

Parent material

Flux

Parent material

Flux

Oxide

Parent material

0 minutes 0 to 0.5 minutes up to 4 minutes above approx. 5 minutes

and the structure is then heated. A burner witha higher heat capacity must be used or higherinductive output must be applied in order torapidly heat the component part. However, itis often impossible to heat heavy massiveparts to the required brazing temperature withthis method. In these cases, the parts must beheated in furnaces in a protective gas atmos-phere.

The residues of hygroscopic fluxes must be re-moved, as these could have corrosive effects.This is done by immersion in hot water or bypickling in pickling baths adapted to the spe-cific parent material. Ultrasonic may also beused to remove these flux residues.

The residues of non-hygroscopic fluxes are notremoved for corrosive considerations. If theymust be removed for other reasons (e.g. lac-quering), this is usually done by mechanicalmeans (e.g. sandblasting).

Figure 17 | Schematic illustration of flux reactions in brazing


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6.3 Gaseous FluxesBrazing joints (V-seams and fillet welds) maybe brazed with gaseous fluxes. In order toclose brazing gaps – in particular if the gapsare narrow and deep - the use of gaseousfluxes alone is not recommendable becausethe flame will not penetrate into the capillarygap. These fluxes are also not suited forchromium-nickel steels. If applicable, gaseousfluxes may be applied in addition to otherfluxes in order to protect the surface againstoxidation.

During the flame brazing operation thegaseous fluxes are reacting with the oxygenfrom the air and forming boric acid, which canbe found a smallest particle in the air, on thebrazed part and the machinery. Since Decem-ber 2010 boric acid has to classified as toxicsubstance in the European Union [22] and thebrazer has to be protected against the boricacid dust.

The active temperature range of gaseousfluxes extends from approx. 750 °C to 1100 °C.

6.4 Brazing With Flux-FormingFiller Metals Copper, copper-tin alloys as well as silver maybe brazed with phosphoric brazing filler metalswithout adding fluxes. The self-fluxing effectof these filler metals can be explained as fol-lows:

When the filler metal melts, the phosphorousincorporated in the filler metals reacts with at-mospheric oxygen to form phosphorous pen-toxide, which reacts with the copper oxide onthe copper surface to form copper metaphos-phate acting as a flux. Copper metaphosphateforms a dark, non-water-soluble film withoutany corrosive elements – see figure 18. As aconsequence, the brazed joints will not requireany post-brazing treatment. If so required,copper metaphosphate may be removed bywashing with diluted sulphuric acid.

Brazing time with BrazeTec Copper Phospho-rous filler metals should also not exceed 3 to 4minutes.

Figure 18 | Typical copper phosphorous brazed joint


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A component is brazeable / solderable (seepage 22) if

a) the parent material is suited for brazing /soldering,

b) the application of one or various brazing /soldering techniques is feasible,

c) the parts can be reliably joined and thenew brazed part is able to meet the spec-ified requirements.

Each one of the three characteristics: mate-rial solderability, constructional solderabilityand procedural solderability depends uponthe parameters: material, production process,

and design engineering, to an extent de-pending on the relevant brazing/solderingapplication.

Table 2 shows the suitability of materials forbrazing.

The annexed Table 6 has a number of rec-ommendations on how to braze the abovematerials. However, this does not necessarilyimply that the joined components will beable to meet all specific operational require-ments. In order to warrant for such quality,the operational circumstances must beknown before selecting a specific brazingtechnique. These conditions are specific to

each workpiece and will differ from case tocase. In particular high-risk cases we adviseyou to consult us for definition of the best-suited brazing parameters.

Brazing has the one major advantage that al-most all materials suited for brazing may bejoined with each other in almost all combina-tions.

Brazing parameters must always be based onwhichever material is the most difficult interms of brazing.

7. Solderability of ComponentsDIN 8514 defines solderability of a component asthe ability of being manufactured by brazing or soldering and thereby being able to meet the specific requirements on that particular componentpart [23].

Group 1 Group 2 Group 3

Materials which can be brazed with universalfiller metals and fluxes and by all standardtechniques.

Materials which require special filler metalsand/or special fluxes but not special brazingtechniques.

Materials which can be brazed only with spe-cial filler metals and special techniques.

e.g.• copper and copper alloys• nickel and nickel alloys• ferrous materials• common steels• cobalt• precious metals

e.g.• aluminium and aluminium alloys• carbide metals, stellite• chromium, molybdenum, tungsten,

tantalum, niobium• materials similar to soft solder

e.g. • titanium• zirconium• beryllium • ceramics

Table 2 | Suitability of Materials for Brazing


20

Categories Brazing/soldering

temp. range

Typical filler metals inthis category Nomen-

clature as in

BrazeTec-nomenclature

Solidustemp.

Liquidus-temp.

Max. admissiblecontinuous op-eration temp. 1)

Major fields of application

°C °C °C °C

Tin-antimony soft solderEN DIN EN ISO 9453& ISO 3677

250 201 Sn95Sb5 Soldamoll 235 235 240 110 Refrigeration industry

Tin-copper soft solders EN DIN EN ISO 9453& ISO 3677

230 – 320 402 Sn97Cu3 Soldamoll 230 (BrazeTec 3) 227 310 110 Copper plumbing for

hot and cold water

Tin-silver soft solders DIN EN ISO 9453& ISO 3677

220 – 260703 Sn96Ag4 Soldamoll 220 221 – 110

Food-processing industry 702 Sn96Ag3 BrazeTec 4 221 224 –

Silver brazing filler metalsDIN EN ISO 17672

650 – 1100

Ag 156 BrazeTec 5600 620 655 200 Electrical industry

Ag 145 BrazeTec 4576 640 680 200 Gas and water plumbing

Ag 134 BrazeTec 3476 630 730 200 Gas and water plumbing

Ag 244 BrazeTec 4404 675 735 200Electrical engineering

Ag 212 BrazeTec 1204 800 830 300

Mangenese containing special-grade brazing filler metalsDIN EN ISO 17672

690 – 1020 Ag 449BrazeTec 4900 680 705 400

Carbide toolsBrazeTec 21/68 980 1030 600

Coppper-phosphorous brazingfiller metal for copper materials DIN EN ISO 17672

650 – 800

CuP 284 BrazeTec Silfos 15 645 800 150 Electrical industry

CuP 279 BrazeTec Silfos 2 645 825 150 Copper-pipe installation

CuP 179 BrazeTec Silfos 94 710 890 150 for gas utilities

Special-grade brazing filler metals for particular applicationsDIN EN ISO 17672

730 – 960Ag 272 BrazeTec 7200 780 780 300 Vacuum engineering

Ag 160 BrazeTec 6009 600 720 200 High-grade steel

Brass brazing filler metals DIN EN ISO 17672

900 – 910Cu 680 BrazeTec 60/40 870 900 300 Galvanized steel pipes

Cu 773 BrazeTec 48/10 890 920 300 Automotive engineering

Nickel-based high-temperaturebrazing filler metals DIN EN ISO 17672

900 – 1200

Ni 710 BrazeTec 897 890 890 – Heating elements

Ni 650 BrazeTec 1135 1080 1135 – EGR-cooler

Ni 620 BrazeTec 1002 970 1.000 – EGR-cooler

Copper-based high-temperaturebrazing filler metals DIN EN ISO 17672

1040 –1120

Cu 110 BrazeTec 801 1085 1085 – High-grade steel

Cu 922 BrazeTec 802 910 1040 – High-grade steel

Cu 925 BrazeTec 803 825 990 – Copper or steel

Aluminium-based brazing filler metals DIN EN ISO 17672

560 – 600 Al 112 BrazeTec 88/12 575 590 200 Heat exchangers

Table 3 | Fluxes for Soldering Metal Materials according DIN EN 29454-1

1) not standadized

8. Annex

DIN EN ISO 9453 orDIN EN 1044

Flux categories Flux base Flux activator Consistency

1 Resin1 With pine resin2 Without pine resin 1 Without activator

2 Activated with halogens3 Activated without halogens

A Liquid

B Solid

C Paste

2 Organic1 Water soluble2 Not water soluble

3 Inorganic

1 Salts1 With Ammonia chloride2 Without Ammonia chloride

2 Acids1 With phosphoric acid 2 With other acids

3 Alkaline 1 With amines and/or ammonia

Table 4 | Filler Metal Categories for Brazing and Soldering


21

Materials BrazeTec brazing filler metal

BrazeTec Fluxes

Technique 1) BrazeTec solder

Fluxes Technique 1)

CuBrazeTec Silfos 2

–

FL / IN ER / PA / VF

BrazeTec 3BrazeTec 4

Soldaflux 7000 FL / ER

BrazeTec Silfos 94

Cu alloys

BrazeTec Silfos 2

BrazeTec hBrazeTec 5600

BrazeTec 4404

Ni + Ni alloys BrazeTec 5600BrazeTec h

FL / IN / ER / AF BrazeTec 3 Soldaflux KFL / ER / INFerrous materials

common steelsBrazeTec 4404 PA / VF Soldamoll 220 Soldaflux K

Cobalt

BrazeTec 60/40BrazeTec s

FL / IN / ER / AF

– – –BrazeTec 48/10PA / VF

BrazeTec 801 –

Cr and Cr/Ni steels

BrazeTec 6009 BrazeTec Special h FL / IN / ER

Soldamoll 220 Soldaflux Z

FL / ER / SI

BrazeTec 897/1002/1135

– PA / VF HB / AFBrazeTec 7200

BrazeTec 801

Precious metals BrazeTec 5600

BrazeTec h FL / ID

Soldamoll 220 Soldaflux K –BrazeTec 7200 AF

Al and Al alloys BrazeTec L88/12 BrazeTec F30/70

FL – – –

(with Mg and/or Si contents ≤ 2 wt%) AF

Cemented carbides

BrazeTec 4900BrazeTec Special h FL

– – –

BrazeTec 49/Cu

BrazeTec 4900BrazeTec Special s IN

StellitesBrazeTec 48/10

BrazeTec Cu/NiN PA / VF

Chromium,BrazeTec 4900 BrazeTec Special h

FL / IN

– – –Molybdenum,AF / PA

Tungsten, tantalum, niobium BrazeTec 21/68 BrazeTec Special s

Zinc– – – Soldamoll 220 Soldaflux K

FL / ER

Antimony SI / HB

TitaniumBrazeTec 7200

–PA (Argon)

– – –BrazeTec SCP 2 VF

ZirconiumBrazeTec SCP 2 –

PA (Argon)– – –

Beryllium VFGraphite

BrazeTec CB 4 –PA (Argon)

– –Metal oxide ceramics VF

Table 5 | : Fluxes for Soldering Metal Materials according DIN EN 29454-1

1) FL=Flame; ER=Electrical resistance; PA=Protective atmosphere furnace; SI=Soldering iron; IN=Inductive; AF=Atmospheric furnace; VF=Vacuum furnace; HB=Hot-air blower

Flux categories Flux type Flux basis Major fields of application Conduct of flux residues

Fluxes for soldering heavy metals

3.2.2. Zinc chloride and/or ammonium chloride and free acids Chromium-containing steels;highly oxidized workpieces

Corrosive3.1.1. Zinc chloride and/or ammonium chloride Chromium-free steels and nonferrous metals,

if residues can be washed off

3.1.1. Zinc chloride and ammonium chloride in organic composition

Chromium-free steels and nonferrous metals,if flux residues cannot be washed off

Partially corrosive2.1.3. Organic acids

2.1.1. Amines, diamines, urea

2.1.2. Organic halogen compounds

1.1.2. Resins with halogen bearing activators

CopperNon-corrosive

1.1.1. Resins without additives

1.1.3. Resins with halogen-free additives

Fluxes for solde-ring light metals

3.1.1. Solder-forming zinc and/or tin chlorides; also with additives

For workpieces that can be washed Corrosive2.1.3. Organic compounds

2.1.2. Organic halogen compounds

Table 6 | Suggestions for Selecting Filler Metals, Fluxes and Techniques


Active brazing [24]

Active brazing is the direct brazing of ce-ramic-ceramic and ceramic-metal joints.The active brazing filler metals used foractive brazing contain components liketitanium, zirconium or hafnium whichpromote wetting by a reaction at thebrazing filler metal / ceramic interface.

Alloy [24]

Compounds of two or more metals arecalled alloys.

Annealing [24]

The majority of metals used for industrialpurposes, e.g. copper, brass, steel fordeep-drawing, are generally strength-ened by cold-forming processes (press-ing, drawing, rolling, etc.). Annealingallows the soft and less strong startingstate to be re-established. Other materi-als like steel or copper-beryllium can behardened and strengthend by cus-tomised heat treatments. It is recom-mended to consider these two groups ofmaterials separately for brazing.

Arc Brazing [1]

Metal arc brazing processes can be sub-divided into gas-shielded metal arc braz-ing (known as gas metal arc brazing inthe US) and gas-shielded brazing with anon-consumable electrode.

The principle of metal arc brazing is al-most identical to that of gas metal arcwelding, i.e. (tungsten) plasma arcwelding with filler wire. The most com-monly used filler wires are copper alloys.The melting ranges of these filler mate-rials are lower than those of the parentmaterial(s). Usually, metal arc brazingprocesses are used with thin steelsheets, which may be coated or un-coated. Due to the lower melting rangeof the filler material, there is less risk ofdamage to any coating as well as lessrisk of the heat affecting the workpiece.Metal arc brazing does not cause signifi-cant melting of the parent material(s).Usually, no flux is necessary.

Assembly Gap [1]

Narrow, mainly parallel gap between thecomponents to be brazed, measured at

A

room temperature.

Automatic Brazing [1]

Brazing in which all operations, includingall auxiliary operations such as changingthe workpiece, are carried out automat-ically.

Bonding Process [1]

Process by which a bond is created be-tween the liquid phase of the filler metaland the solid parent metal due to met-allurgical reaction.

Boiling Point [25]

The boiling point of an element or a sub-stance is the temperature at which thevapor pressure of the liquid equals theenvironmental pressure surrounding theliquid.

Braze Welding [24]

If the surfaces on the workpiece to bejoined are more than 0.5 mm apart, thisis considered to be a (brazing) joint(smaller distance = brazing gap). Thework procedures and temperature distri-bution for braze welding and for fusionwelding are identical. In braze welding,relatively large amounts of brazing fillermetal are used. That is why silver-freebrazing fillers BrazeTec 60/40 andBrazeTec 48/10 are almost always used.If a component with a brazing gap can-not tolerate heating over the wholelength of the surface to be brazed, brazewelding may also be applied.

Brazeability [23]

A component is considered to be solder-able / brazeable if the parent material issuited for soldering/brazing, if one ormultiple soldering / brazing techniquesmay be applied, if the designated partshave been constructed in a mannersuited for soldering / brazing and thepart thus manufactured is safe andsuited for the intended use.

Brazing [1]

Joining process using filler metal with aliquidus temperature above 450 °C.

B

Brazing Filler Metal [1]

Added metal required for brazed joints,which can be in the form of wire, inserts,powder, pastes, etc.

Brazing Fixtures [26]

Fixtures are used to firmly position braz-ing parts and to achieve dimensional sta-bility. Brazing fixtures must beparticularly adapted to the applied braz-ing method and its specific require-ments.

Brazing Gap [1]

Narrow, mainly parallel gap between thecomponents to be brazed, measured atthe brazing temperature.

Braze Metal [1]

Metal formed by the brazing process.NOTE Because the filler metal hasmelted, its chemical composition maychange due to reactions with the parentmaterial(s).

Brazing Stop-Off [1]

Substance used to prevent undesirablespreading of molten filler metal.

Brazing Temperature [1]

Temperature at the joint where the fillermetal wets the surface or where a liquidphase is formed by boundary diffusionand there is sufficient material flow.

With some filler metals, this is below theliquidus temperature of the filler metal.

Brazing Time [1]

Time period for the brazing cycle.

Bright, Metallically Bright [24]

Visible oxide films (rust and scales) aswell as grease and grime must be re-moved prior to brazing. Thin oxide films(e.g. tarnish) need not be removed fromthe workpiece if flux is used for brazing.

Butt Joints [27]

Joint connections between two parentmaterials without any overlapping.

Capillary Attraction [1]

Force caused by surface tension whichdraws the molten filler metal into thegap between the components beingjoined, even against the force of gravity.

Cemented Carbide [24]

Cemented carbides are sintered metalsmade from powder mixtures of naturallyhard materials. They contain a high pro-portion of metal carbides, most com-monly tungsten carbide (WC). Cobalt inconcentrations of between 5-13 wt% is

C

22

9. Technicalglossary

Solderabilityof the

structure

Materialsolderability

Constructionalsolderability

Proceduralsolderability


mainly used as the binder metal. In ex-ceptional cases the cobalt content maybe higher.

Ceramics

Brazing of ceramics– see Active brazing.

Clearance

Please refer to brazing gap.

Cooling Time [1]

Time during which the joint cools downfrom the brazing temperature to ambi-ent temperature. It can include the timenecessary for the post heat treatment ofthe brazed parts.

De-wetting [1]

Separation of solid filler material which,although it had spread over the surfacesof the components to be joined, hadfailed to bond to them because of e.g.inadequate cleaning or fluxing.

Dew Point [25]

This is the temperature at which thewater vapour in the air becomes satu-rated and condensation begins.

Diffusion [24]

In general, the term diffusion refers to amacroscopic mass transport caused bymovement of individual atoms alongpaths which are larger than the inter-atomic distance.

Diffusion Zone [1]

Layers formed during brazing with achemical composition that is differentfrom that of the parent material(s) andthat of the braze metal.

Dip Soldering [1]

The components are soldered by dippingthem in a bath of liquid filler metal. Theyare wetted with flux before dipping. Thedipping speed is selected so that it is justhigh enough to ensure that each compo-nent reaches the soldering temperatureduring dipping. A visible sign of this isthe presence of a positive meniscus(concave surface) at the interface be-tween the filler metal surface and thecomponent.

The component to be soldered may beeither cold or preheated before dipping.

Dwell Temperature

See equalizing temperature.

Dwell Time

See equalizing time.

D

Effective Time [1]

time during which the flux remains ef-fective during the brazing operation. It isdependent on the procedure used.

Effective Temperature Range [24]

The temperature range in which fluxesor protective gas atmospheres are effec-tive.

Electron-Beam Brazing [1]

Heat is generated in the component, atthe joint being brazed, by absorption ofa focussed electron beam. The process isusually carried out under a vacuum.

Equalizing Temperature [1]

Temperature at which the componentsbeing joined are held so that they areuniformly heated through. It is lowerthan the solidus temperature of the fillermetal.

Equalizing Time[1]

Time during which the components to bebrazed are held at the equalizing/pre-heating temperature.

Eutectic Alloys [24]

Just like pure metals, eutectic alloys havea melting point rather than a meltingrange. The best-known example in braz-ing technology of a eutectic alloy isBrazeTec 7200, comprising 72 wt% silverand 28 wt% copper and with a meltingpoint of 780 °C.

Filler Metal Foil [1]

Brazing filler metal or brazing filler metalpowder as foils, with or without binder.

Filling Degree [28]

Percentage of the total brazing gap vol-ume filled up by the brazing alloy.

Flame Brazing [1]

A gas-operated torch is used as the heatsource. The torch is adjusted to producea neutral or slightly reducing flame.

Flammable Gases [24]

Pipes used for transporting gases forpublic and private gas utility companiesin Germany must be brazed. In accor-dance with the DVGW (German associa-tion for gas and water ) working sheetGW2, silver brazing filler metals BrazeTec4576, 3476 and 4404 and also phospho-rous-containing brazing filler metalsBrazeTec S 94 and S 2 are permitted. Ifsulphur-containing media (e.g. engineoils, air from stalls, etc.) might possibly

F

E come into contact with the brazed joints,phosphorous-containing brazing fillermetals may not be used. In accordancewith DIN ENISO 9539 [29] acetylenepipes must be brazed with filler metalswhich do not contain more than 46 wt%Ag and not more than 36 wt% Cu(BrazeTec 4576 or 4404).

Flow Path [1]

Distance through which the molten fillermetal flows in the joint.

Flux [1]

Non-metallic material which, whenmolten, promotes wetting by removingexisting oxide or other detrimental filmsfrom the surfaces to be joined and pre-vents their re-formation during the join-ing operation.

Flux Vapours [24]

The vapours that are produced whenbrazing with fluxes are irritating and cor-rosive. Extraction of the vapours is al-ways recommended. If the relevantapplicable WEL-values (Workplace Expo-sure Limits) are exceeded, brazing workmust be carried out with extraction ofthe vapours.

Furnace Brazing [1]

The components to be brazed are heatedby means of radiant heat and/or convec-tion of the hot gas in the furnace. Thecomponents are fixed relative to eachother. The brazing filler metal is put inplace before heating starts. Usually, theprocess is carried out without flux in a re-ducing-gas atmosphere or in a vacuum.In some cases, an inert protective gas at-mosphere may be used and/or flux, e.g.for aluminium alloys.

Galvanising [24]

If the surfaces of the components are tobe galvanised after brazing, silver braz-ing filler metals with low meltingpoints are preferred because fluxresidues are easy to remove. In gen-eral, cadmium-free brazing filler metalsform smoother fillets. In particularcases, silicone silver brazing filler met-als are recommended. When usinghigher melting point brazing filler met-als such as BrazeTec 60/40 or BrazeTec48/10, the flux residues must be re-moved mechanically.

Gap Brazing [24]

Gap brazing is the joining of compo-nents, whereby a narrow gap betweenthe components is preferably filled with

G

23


24

filler metal by capillary pressure. Work-pieces with gap widths below 0.5 mmare brazed using the gap brazing tech-nique.

Gasous Fluxes [24]

Gaseous fluxes are fluxes that are usu-ally formed from volatile liquid mix-tures consisting of boric acid esters anda highly volatile solvent as a transportmedium. They are only used for flamebrazing. In this technique, the flow offuel gas is passed through the liquidmixture and is enriched with flux. Theflux is then passed on to the compo-nent to be brazed by the flame and re-moves the oxides. A disadvantage ofusing gaseous flux is that it is only ef-fective above approx. 750 °C and doesnot penetrate into narrow gaps, thuslimiting thorough brazing. During theflame brazing operation the gasesousfluxes are reacting with the oxygenfrom the air and forming boric acid,which can be found a smalles particlein the air, on the brazed part and themachinery. Since Dezember 2010 boricacid has to be classified as toxic sub-stance in the European Union [21] andthe brazer has to be protected againstthe boric acid dust.

Heating Time [1]

Time during which the brazing tempera-ture is reached. It includes the equaliz-ing (preheating) time and can alsoinclude other times, e.g. the degassingtime.

High Temperature Brazing [4]

Joining process in inert gas atmosphereor vacuum atmosphere with liquidustemperatures over 900 °C.

Holding Time [1]

Time during which the joint is kept at thebrazing temperature.

Induction Brazing [1]

Heat is generated by an alternating cur-rent induced in the components to bebrazed, Normally, this kind of brazing iscarried out in air with flux, but protectiveatmosphere may also be used.

The energy density induced in the com-ponents decreases rapidly from the sur-face towards the interior. The depth ofpenetration is a function of frequency.Medium frequencies (1 000 Hz to 10 000

H

I

Hz) give a greater depth of penetrationthan high frequencies (100 kHz to sev-eral MHz).

Inert Gas Atmosphere [1]

Gas which prevents the formation of ox-ides during the brazing process.

Intercrystalline Diffusion [25]

Filler metal diffusion along the grainboundary of the parent material.

Interfacial Corrosion [24]

Crevice corrosion and knife-edge corro-sion are popular names for a form of in-terfacial corrosion. This occurs forexample on stainless steel componentswhich have been brazed with zinc-con-taining filler metals and which come intocontact with aqueous media. The steelsurface is usually visibly corroded at theedge and under the brazed joint. Thedanger of corrosion is reduced by brazingwith Zn-free filler metals such asBrazeTec 6009 (Ag 60 wt%, Cu 30 wt%,Sn 10 wt%) and flux. When furnacebrazing (without flux), e.g. using copperor nickel based alloys as the filler metals,there have not yet been any incidents ofknife-edge corrosion.

Lap Joints [27]

Joints of two overlapping parent materi-als.

Laser beam Brazing [1]

Laser beam brazing can be carried outwith CO2 or Nd:YAG lasers operating in acontinuous or pulsed mode. The fillermetal is usually applied as filler wire oras brazing paste. A relatively new appli-cation for laser beam brazing is the join-ing of steel sheets, e.g. in theautomobile industry. Laser beam brazingprocesses may also be carried out undera shielding gas or in vacuum.

Liquidus Temperature [24]

The liquidus temperature is the uppertemperature limit of the melting rangeor the melting interval. The filler metalis completely liquid above this tempera-ture.

Manual Brazing [1]

Brazing in which all operations are car-ried out manually.

Maximum Brazing Temperature [24]

The maximum brazing temperature isthe temperature up to which the parentmaterial and the filler metal are not

L

M

damaged, i.e. heat sources must be cho-sen to generate adequate temperature-time profiles for the workpiece.

Mechanized Brazing [1]

Brazing in which all the main operations,except the handling of the workpiece,are carried out mechanically.

Melting Point [25]

The melting point of a solid is the tem-perature at which it changes state fromsolid to liquid. At the melting point thesolid and liquid phase exist in equilib-rium.

Melting Temperature Range of theFiller Metal [1]

Temperature range extending from thecommencement of melting (solidustemperature) to complete liquefaction(liquidus temperature). Some filler met-als have a melting point rather than amelting range.

Operating Temperature [24]

Increased operating temperatures al-most always lead to considerable loss ofstrength in brazed joints. The maximumoperating temperatures stated in techni-cal data sheets or product informationshould not be exceeded over long peri-ods. Higher temperatures are generallypermitted for short periods if the brazedjoints are not subject to significant loads.

Oxygen Content

The oxygen content of supplied inert orprotective gases or of the furnace atmos-pheres are stated in vpm or ppm (1 vol-ume part per million).

Partial Alloying [24]

Partial alloying is the strong diffusion ofthe components of the brazing fillermetal into the parent material. As thediffusion is dependent on both time andtemperature, the holding time at thebrazing temperature should be kept asshort as possible, especially for hightemperature brazing filler metals, inorder to avoid partial alloying of the basematerial (erosion) and possible forma-tion of brittle phases in the transitionzones.

Parent material [1]

Material being brazed.

Partial Pressure [24]

Partial pressure is the pressure that maybe attributed to a particular component

O

P


25

in gas compounds, e.g. air. The partialpressure corresponds to the total pres-sure that the particular componentswould exert if they were the only singleelement filling the entire volume. In vac-uum brazing, a gas is added to the vac-uum atmosphere to prevent vaporisationof the alloy components of the filler met-als or the parent materials.

Preformed Filler Metals [24]

Filler metals come in the followingforms: wire sections, wire rings, bentpieces of wire, discs, washers, square orrectangular sheet sections and stampedsheets. In particular cases, e.g. for sur-face brazing, shaped pieces of fillermetal must be used for brazing as therate of flow into narrow surface gaps isconsiderably smaller than into the freefillet.

Preheating Temperature

See equalizing temperature.

Preheating Time

See equalizing time.

Protective Atmosphere for Brazing [1]

Gas atmosphere or vacuum round acomponent, either to remove oxide orother detrimental films on the surfacesto be joined or to prevent the re-forma-tion of such films on surfaces which havepreviously been cleaned.

Reconditioning [26]

Reconditioning may be required depend-ing upon brazing process and the mate-rials used. Residues of fluxes, brazingfiller metal resists and binders should beremoved by rinsing, pickling or mechan-ical means. The brazing connection mustbe designed to allow any required recon-ditioning work and easy removal of anyresidues.

Reducing Gas Atmosphere [1]

Gas which reduces oxides owing to itshigh affinity for oxygen. Materials sensi-tive to oxidation, such as alloys withmore than 0.5 % aluminium, titanium orzircon cannot be brazed without flux inreducing protective gas atmospheres[30]. Parts brazed in protective gas at-mospheres are metallically bright and donot require any subsequent treatment.

Resistance Brazing [1]

Heat is generated in the components atthe joint by the resistance to the passageof an electric current. This electrical heat-ing enables the components to bebrazed either indirectly or directly.

R

Sandwich Brazing Alloys [24]

Layered filler metals consist of a copperlayer or a nickel mesh coated with fillermetals on both sides. They are used forbrazing cemented carbides and are ap-plied to compensate internal tensioncaused by different thermal coefficientsof expansion or contraction.

Salt Bath Brazing [1]

The components are heated by dippingthem in a bath containing a mixture ofmolten salts. The bath is made of a suit-able material. Many salt mixtures havealso a flux action. The composition of thesalt mixture depends on the nature ofthe parent metal and of the filler metal.Filler metal preforms are placed in theimmediate proximity of the joint areaprior to immersion.

Solderability

See Brazeability.

Soldering [1]

Joining process using filler metal with aliquidus temperature of 450 °C or less.

Soldering Irons [1]

Soldering irons are used exclusively forsoldering. They consist of a metal bit(copper) that is heated, for exampleelectrically or by using a burner. The heatand also the molten solder are trans-ferred to the component by contact ofthe metal bit with the component, anda soldered joint is thus created.

Soldering with Soldering Iron [1]

Heating the soldering point and meltingthe filler metal are carried out using asoldering iron operated manually or me-chanically. A soldering iron with a heatcapacity, shape and tip suitable for thesoldering point is used. Both of the com-ponents to be joined and the filler metalare brought to the brazing/solderingtemperature using a flux, either sepa-rately or in the form of a flux-cored fillermetal.

Solidus Temperature [24]

The solidus temperature is the lowertemperature of the melting range ormelting interval. The filler metal is com-pletely solid below this temperature.

S Step Brazing [28]

The brazing of secondary joints on com-ponent parts with a filler metal with alower brazing temperature without inter-fering with the primary brazed joints.

Strength of Brazed Parts [26]

The strength of brazed joints dependsupon the type of brazing alloy, engineer-ing design, capillary joint, overlap, theparent material and its preparatory treat-ment as well as overall preprocessing.The quality and thus also stability ofbrazed joints depends upon the chosenprocesses. It is advisable to achieve aspecified shearing load. Strength valuesshall be determined per componentpart. Please refer to manufacturer infor-mation for reference values.

Surface Brazing [24]

Surface brazing is coating using brazingtechniques. The coatings can be used forprotection against wear and corrosion.

T-Butt [27]

The parts butt square (T-shaped) on eachother.

T

Brazing Alloy Layer

Intermediate Copper Layer

Brazing Alloy Layer


26

Temperature-Time Scheme [31]

Thermal Influence Zone [1]

That area of the base materials affectedby the brazing process.

Thermocouple [25]

A thermocouple (thermal converter) con-sists of two different metals connectedto each other at one end. Thermocouplesare used for measuring temperatures atcomponent parts and/or the atmos-phere.

Torches [24]

Torches are instruments for heating com-ponents in regular atmosphere. Thereare torches for different gaseous combi-nations: acetylene/oxygen;acetylene/intake air; propane/oxygen;propane/intake air; natural gas/oxygen,natural gas/compressed air or hydrogentorches. The selected gas combinationand size of the burner head determinethe time required for brazing.

Total Time [1]

Period which includes the heating time,the holding time and the cooling time

Transition Zone

See diffusion zone.

Vacuum, Vacuum Brazing [1]

pressure sufficiently below atmosphericso that the formation of oxides will beprevented to a degree sufficient for sat-isfactory brazing, because of the low par-tial pressure of the residual gas. As avacuum can only eliminate oxides to avery limited extent, preparatory cleaningof the surfaces to be wetted is of thegreatest importance.

V

Vacuum Brazing Alloys [24]

All those brazing filler metals with alloycomponents developing high vapourpressures at brazing temperature are notsuited for a vacuum brazing filler metal,for example all filler metals containingvolatile elements such as cadmium orzinc. Brazing in a vacuum is usually donein furnaces, with resistance-heated or in-duction-heated vacuum furnaces beingpredominantly used.

While flux and gases may becometrapped in brazing gaps when brazing inatmosphere, this is virtually never thecase when brazing in a vacuum, thus re-sulting in brazed joints with a good de-gree of filling and high strength.

Vapour Pressure [25]

Vapour pressure is a gas pressure de-pendent upon substance and tempera-ture. In clear terms, vapour pressure isthe ambient pressure below which liq-uids - held at constant temperature -begin to dissolve into a gaseous state ofaggregation. If there are various sub-stances in the examined system, themeasured pressure of the gaseous phaseis composed of the partial pressures ofthese various substances.

Wetting

In brazing technology, wetting is thespreading of the filler metal over the sur-face of the workpiece to be joined [1].Filler metals only wet the base materialif the surfaces to be brazed and the fillermetal are metallically bright. Further-more, the surfaces to be brazed and thefiller metal must at least have reachedthe working temperature of the used

W

filler metal and at least one part of thefiller metal must readily form an alloywith the base material to be brazed [24].

Wetting Angle

See 3.1, page 8

Working Temperature [32]

The working temperature is the lowestsurface temperature at the point to bebrazed at which the brazing alloy wetsthe materials to be joined or at which aliquid phase forms via interfacial diffu-sion. The working temperature is not de-fined in any standard since publication ofISO 857-2.

α

Brazing temperature

Dwell temperature

Dwell time

Heating time Holding time Cooling time

Time

Tem

pera

ture

Brazing timeTotal time


27

[1] DIN ISO 857-2:2007-05: Welding and allied processes Vocabulary Part 2: Solderingand brazing processes and related terms-First Edition

[2] Massalski, T.B.: Binary Alloy Phase Diagrams, ASM International (1996)

[3] Zareamba, P.: Hart- und Temperaturlöten, S. 10, DVS Verlag (1988)

[4] N.N.: Technik, die verbindet, Band 1, S. 3–4, Degussa AG (1987)

[5] Dorn, L.: Hartlöten und Hochtemperaturlöten, S. 11, expert Verlag (2007)

[6] Zeramba, P.: Hart- und Temperaturlöten, S. 8, DVS Verlag (1988)

[7] Dorn, L.: Hartlöten und Hochtemperaturlöten, S. 21, expert Verlag (2007)

[8] Wuich, W.: Löten, S. 55, Vogel-Verlag (1972)

[9] Zimmermann, K.: Technik, die verbindet, Band 4, S. 28, Degussa AG (1990)

[10] Beckert, M.: Grundlagen der Schweißtechnik – Löten, S. 32, VEB Verlag Technik Ber-lin (1973)

[11] N.N.: Grundlagen des Lötens (L), Degussa AG (1996)

[12] www.innobraze.com/

[13] DIN EN ISO 9453:2006-12: Soft Solder Alloys - Chemical Compositions and Forms-Se-cond Edition

[14] DIN EN DIN EN ISO 17672:2010-11: Brazing Filler metals-First Edition

[15] http://www.cuprobraze.com

[16} Weise, W., Malikowski W., Krappitz, H.: Verbinden von Keramik mit Keramik oderMetal durch Aktivlöten unter Argon oder Vakuum, Dagussa-Hüls AG (1999)

[17] COMMISSION REGULATION (EC) No 494/2011 amending Regulation (EC) No1907/2006 of the European Parliament and of the Council on the Registration, Eva-luation, Authorisation and Restriction of Chemicals (REACH) as regards Annex XVII(Cadmium)


[19] Müller, W.: Löttechnik, S. 60, DVS Verlag (1995)

[20] DIN EN 29454-1:1994-02: Soft soldering fluxes - Classification and requirements -Part 1: Classification, labelling and packaging

[21] DIN EN 1045:1997-08: Brazing - Fluxes for Brazing - Classification and Technical Deli-very Conditions

[22] COMMISSION REGULATION (EC) No 790/2009 of 10 August 2009 amending, for thepurposes of its adaptation to technical and scientific progress, Regulation (EC) No1272/2008 of the European Parliament and of the Council on classification, labellingand packaging of substances and mixtures

[23] DIN 8514:2006-05: Brazeability, Solderability

[24] http://www.technicalmaterials.umicore.com/en/bt/ (19.07.2013)

[25] Wikipedia.org/wik (19.07.2013)

[26] DIN 65169:1986-10; Aerospace; brazed and high-temperature braed components,directions for design

[27] DIN 1912-4:1981-05; Zeichnerische Dartstellung Schweißen, Löten

[28] Müller, W.: Löttechnik, S. 2f, DVS Verlag (1995)

[29] DIN EN ISO 9539:2010-05; Gas welding equipment - Materials for equipment usedin gas welding, cutting and allied processes


[31] Prozesskontrolle beim Hochtemperaturlöten, DVS Merkblatt 2607 (2008)

[32] DIN 8505-1:1979-05: Löten; Allgemeines, Begriffe

Literature

Our particulars and statements on our products and equipment as well as installations and

processes are based upon extensive research and experience in applications engineering.

We impart these findings in speech and writing to the best of our knowledge, and in

doing so do not accept any liability extending beyond that stipulated in individual agree-

ments. We reserve the right to technical alterations in the course of technical progress.

Our technical services are available if so required for further consultation and to assist with

finding solutions for any problems arising in production and application.

However, this shall not release users from their obligation to verify our data and recom-

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property rights and to applications and procedures we did not specify in writing, in parti-

cular for export deliveries. In the event of damages, our liability obligations are restricted

to compensation in identical scope and quality as is provided for quality defects in our Ge-

neral Terms and Conditions.


The information and statements contained herein are provided free of charge. They are believed to be accurate at time of publication, but Umicore makes no warranty withrespect thereto, including, but not limited to, any results to be obtained or the infringe-ment of any proprietary rights. Use or application of such information or statements is atthe user's sole discretion, without any liability on Umicore's part. Nothing herein shall beconstrued as a license or recommendation for use that infringes upon any proprietaryrights. All sales are subject to Umicore's General Conditions of Sale and Delivery. © 2013 Umicore AG & Co. KG. the Federal Republic of Germany. – 1. Edition, 10/2013 02

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