oSIST prEN 14324:2017

SLOVENSKI STANDARD
01-september-2017
Trdo spajkanje - Navodilo za uporabo trdo spajkanih spojev
Brazing - Guidance on the application of brazed joints
Hartlöten - Anleitung zur Anwendung hartgelöteter Verbindungen
Brasage fort - Guide d’application pour les assemblages réalisés par brasage fort
Ta slovenski standard je istoveten z: prEN 14324
ICS:
25.160.50 Trdo in mehko lotanje Brazing and soldering
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2017
ICS 25.160.50 Will supersede EN 14324:2004
English Version
Brazing - Guidance on the application of brazed joints
Brasage fort - Guide d'application pour les assemblages Hartlöten - Anleitung zur Anwendung hartgelöteter
réalisés par brasage fort Verbindungen
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee
CEN/TC 121.
If this draft becomes a European Standard, CEN members are bound to comply with the CEN/CENELEC Internal Regulations
which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

This draft European Standard was established by CEN in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC
Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are
aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without
notice and shall not be referred to as a European Standard.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 14324:2017 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Joint design . 7
4.1 Principle . 7
4.2 Types of joint . 7
4.3 Assembly gap and brazing gap . 8
4.3.1 General . 8
4.3.2 Influence of brazing filler materials . 11
4.3.3 Influence of parent material . 11
4.3.4 Influence of dissimilar parent materials . 11
4.3.5 Influence of surface finish . 12
4.3.6 Influence of atmospheres or fluxes . 12
4.4 Surface preparation . 12
4.5 Stress distribution in service . 13
4.6 Application of filler material . 13
4.7 Assembly . 13
4.8 Good brazing design . 13
5 Materials . 13
5.1 Parent materials . 13
5.1.1 Basic considerations . 13
5.1.2 Special considerations . 14
5.2 Filler materials . 16
5.2.1 General . 16
5.2.2 Forms available . 17
5.2.3 Applications . 17
5.3 Fluxes . 18
5.3.1 General . 18
5.3.2 Flux removal . 18
5.4 Atmospheres . 19
5.4.1 Protective . 19
5.4.2 Vacuum atmospheres for brazing . 19
5.5 Safety . 19
6 Methods of brazing . 21
7 Heat treatment . 21
8 Inspection . 21
Annex A (informative) Examples of brazed assemblies . 22
Annex B (informative) Typical examples of joint design . 24
Annex C (informative) Filler materials most commonly used for combinations of parent
materials . 29
Annex D (informative) Suitability of brazing filler material classes for the commoner
brazing methods . 30
Annex E (informative) Methods of brazing . 31
E.1 Flame brazing . 31
E.2 Induction brazing . 34
E.3 Resistance brazing . 35
E.4 Furnace brazing. 36
E.5 Immersion brazing . 40
E.6 Special methods . 42
Bibliography . 45

European foreword
This document (prEN 14324:2017) has been prepared by Technical Committee CEN/TC 121 “Welding
and allied processes”, the secretariat of which is held by DIN.
This document is currently submitted to the CEN Enquiry.
This document will supersede EN 14324:2004.
In comparison to the previous edition, the main changes are:
a) the normative references have been updated;
b) the document has been revised editorially.
Introduction
The purpose of this document is to provide information and guidance to users whose knowledge of
brazing is limited, either regarding the whole process or in some specific areas. It is not intended to
replace textbooks but to make readily available certain important information and to prevent some
common errors.
Brazing techniques offer a wide field for joining, cladding, building up and comparable applications
where brazing filler materials can be used. Structures similar to brazed joints can be achieved by arc
brazing processes (MIG, TIG, plasma), infra-red brazing and electron beam brazing, which are better
described as braze welding.
Where the word 'material' is used for components, they can be metallic or non-metallic, except when
the component can only be metallic, when it is so described. The same usage applies to filler materials,
although the use of non-metallic filler materials is very limited.
1 Scope
This European Standard gives guidance on the application of brazing and the manufacture of brazed
joints. This standard gives an introduction to brazing and a basis for the understanding and use of
brazing in different applications. Because of the wide range of applications of brazing, this standard
does not give detailed guidance that might be product specific. For such information, reference should
be made to the appropriate product standard or, for applications where this does not exist, the relevant
criteria should be clearly established before any brazing is undertaken.
This standard covers joint design and assembly, material aspects for both parent material and filler
materials, brazing process and process variables, pre- and post-braze treatment and inspection.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
EN 1045, Brazing - Fluxes for brazing - Classification and technical delivery conditions
EN 12797, Brazing - Destructive tests of brazed joints
EN 12799, Brazing - Non-destructive examination of brazed joints
EN 13134, Brazing - Procedure approval
EN ISO 13585, Brazing - Qualification test of brazers and brazing operators (ISO 13585)
EN ISO 17672:2016, Brazing - Filler metals (ISO 17672:2016)
EN ISO 18279, Brazing - Imperfections in brazed joints (ISO 18279)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
brazing
joining process in which a filler material is used which has a liquidus temperature above 450 °C, but
below the solidus of the parent material, and which is mainly distributed in the brazing gap by capillary
attraction
Note 1 to entry: Other joining methods exist (see E.6.3).
3.2
brazed joint
result of a joining process where the parent materials are not melted and the filling material and braze
material have different chemical compositions compared to the parent materials
3.3
brazing gap
narrow, mainly parallel gap at the brazing temperature between the components to be brazed (see
Figure 1 and 4.3.4)
3.4
assembly gap
fit up
narrow, mainly parallel gap at room temperature between the components to be brazed (see Figure 1
and 4.3.4)
g < g
2 1
a) Constrained butt joint
g > g
2 1
Shaded component has higher coefficient of expansion.
b) Tube joint (dissimilar materials)
Key
A assembly at ambient temperature
B assembly at brazing temperature
g assembly gap
g brazing gap
Figure 1 — Assembly gap and brazing gap
4 Joint design
4.1 Principle
The brazing process depends upon capillary flow of a molten brazing filler material between parts
separated by a narrow gap. The filler material has a different composition from the components to be
brazed. This compositional difference may affect the properties of the assembly in service, e.g. at
elevated temperature, in corrosive media or under fatigue loading. In addition the properties of the
parent material of the components to be brazed can be affected by the brazing cycle.
4.2 Types of joint
There are basically two types of joint as shown in Figure 2. In practice very few assemblies are as
simple as the basic types shown in Figure 2 (see Annex A).
a) Lap
b) Butt
Figure 2 — Basic joint types
Lap joints are generally used because they are easier to fabricate and offer increased strength. Butt
joints are used where adequate strength is readily obtained, e.g. where the mechanical properties of the
parent materials are lower than those of the brazed joint, or where the thickness and/or length of a lap
joint is undesirable.
It should be noted that the useful overlap for a lap joint in shear is related to the thickness of the thinner
component; beyond the optimum overlap there is little to be gained in joint strength by increasing the
overlap length.
4.3 Assembly gap and brazing gap
4.3.1 General
The areas of a brazed assembly are defined as shown schematically in Figure 3.
Perhaps the most critical feature in brazing is the control of the brazing gap, i.e. the gap at the brazing
temperature, between the components to be brazed and through which the filler material has to flow
by capillary action. There are several factors that influence the choice of the brazing gap and which have
to be taken into consideration. It is essential to recognise that where joints are to be made between
different parent materials, the assembly gap (fit up) will usually have to be different from the brazing
gap (see 4.3.4).
NOTE The assembly gap may need to be larger or smaller than the brazing gap, depending on the thermal
expansion coefficients of the materials, the configuration and the brazing process.
Different filler materials require different gaps even within the same group, as can be seen from the
typical ranges given in Table 1, but the optimum gap may also be affected by a number of other joint
parameters (see example in Figure 4), e.g.:
— parent material(s);
— geometry of the joint;
— surface finish of the faying surfaces;
— use of a flux or protective atmosphere;
— careful control of brazing temperature and heating rate;
— brazing process.
Table 1 — Typical brazing gaps
a
Filler metal class Brazing gap
according to EN ISO 17672 mm
Al 0,05 to 0,25
Ag 0,05 to 0,30
CuP 0,05 to 0,30
Up to 0,15
Cu
0,05 to 0,20
Ni Up to 0,15
Au Up to 0,10
a
Brazing gap will depend on the selected filler materials, the brazing process
and the brazing conditions.
a) Simple brazed assembly
b) Section through assembly in a)
Key
parent material
parent material affected by brazing (heat affected zone (HAZ))

diffusion-transition zone
braze material
NOTE Extent of HAZ will vary with materials and brazing process.
Figure 3 — Schematic of brazed assembly
Key
1 mechanized flame brazing with flux
2 hand flame brazing with flux
Figure 4 — Schematic of differences in brazing gap ranges with different brazing processes (in
this example for mild steel brazed with an Ag filler materials)
4.3.2 Influence of brazing filler materials
Those types with the shortest melting range, often containing significant additions of temperature
depressant elements (e.g. Si, B, P and Zn) exhibit enhanced fluidity and excellent capillary penetration.
This also applies to most eutectic compositions and many pure metals. Conversely, those filler materials
having wide melting ranges will generally have better wide gap filling characteristics and are more
suitable for brazing when gaps are at the upper end of the stated range.
4.3.3 Influence of parent material
For those parent materials that are not readily soluble in the brazing filler material, or do not undergo
mutual interaction to form alloy layers, gaps may, in general, be tighter than with those combinations
where significant alloying occurs. Extensive inter-alloying will impair the fluidity of the brazing filler
material and necessitate the use of wider brazing gaps to ensure complete penetration of the joint by
the brazing filler material.
4.3.4 Influence of dissimilar parent materials
When dissimilar parent materials, of different coefficients of thermal expansion, are to be joined, care
has to be exercised in designing the joint in order to obtain the correct brazing gap (see Figure 5). In
extreme cases, joint gaps may close completely or open excessively at brazing temperature resulting in
non-penetration or non-retention of the brazing filler material, respectively. Given that the brazing gap
is the essential parameter, the assembly gap (to which the components will be machined) has to be
calculated from the expansion coefficients of the parent materials, the sizes of the components and the
brazing temperature.
This problem becomes greater:
— as the size of the brazed assembly increases;
— as the brazing temperature becomes higher;
— as the thermal expansion differential widens.
Key
1 molybdenum
2 steel
A assembly at ambient temperature
B assembly at brazing temperature
d outer diameter of steel part (before brazing)
s
d inner diameter of molybdenum part (before brazing)
m
a assembly gap
b brazing gap
Thermal expansion coefficient α
α steel > α molybdenum
Figure 5 — Influence on the brazing gap of dissimilar parent materials with different thermal
expansion coefficients (schematic)
4.3.5 Influence of surface finish
Too coarse or too fine a surface finish will adversely affect the filling of the joint gap. The flow of the
filler material may be influenced by the surface finishes of the joint materials.
4.3.6 Influence of atmospheres or fluxes
Processes using a protective atmosphere or a vacuum will tolerate tighter joint gaps, with given brazing
filler materials, than an equivalent process where a flux is used. Unless joint gaps are adequate, flux and
gas pockets will be by-passed and become entrapped in the finished joint.
4.4 Surface preparation
The component parts of a joint should be clean and properly fitting. When required by the brazing
method, oxide, grease and oil should be removed by chemical, thermal and/or mechanical methods.
This may involve degreasing, pickling, scratch brushing and other similar processes. The surface of the
component within the brazed joint should not be polished. A roughened surface will assist filler
materials flow particularly in the direction of machining. To improve the fit-up it may be necessary to
modify the surface by methods such as knurling. To improve wettablilty of materials such as nickel
alloys containing titanium and aluminium, and ceramics, it may be necessary to cover the surfaces with
a suitable material, e.g. by plating or metallizing.
To prevent the flow of filler materials outside the joint area, it may be necessary to apply a 'stopping-off'
agent. Care should be taken that this does not penetrate into the capillary joint gap and inhibit flow.
The degree of cleanliness required depends upon the ultimate quality required of the component and
also the brazing process to be used. The degree of preparation is most severe for flux-free controlled
atmosphere brazing at higher temperatures.
4.5 Stress distribution in service
Figure B.1 illustrates design modifications which endeavour to remove high stress concentrations from
joint edges and distribute the stress more evenly in the parent materials.
4.6 Application of filler material
The brazing filler material is available in various forms (see 5.2.2).
For hand torch brazing applications, the brazing filler material is generally hand fed as rod or wire but
may be pre-placed. In mechanized brazing applications, the brazing filler material is either pre-placed
or automatically fed. In furnace brazing it has to be pre-placed. Examples of filler material placement
are shown in Figure B.2.
The point at which the filler material is applied can greatly affect the quality of the joint. Internal pre-
placement can also serve to demonstrate that capillary flow through the joint has occurred.
4.7 Assembly
It is essential, when designing joints, to ensure that the component parts will retain the required
relationship during the brazing process. There are several effective methods of achieving this (see
Figure B.3).
4.8 Good brazing design
Examples of good brazing design are given in Tables B.1 and B.2.
5 Materials
5.1 Parent materials
5.1.1 Basic considerations
The wide range of materials in current use precludes the listing of every grade which is amenable to
joining by the brazing process. General categories are listed here for guidance purposes but other less
common materials may well be applicable. If an unlisted material is specified, advice should be sought
from the brazing filler manufacturer.
a) Aluminium and its alloys. Pure aluminium, aluminium-zinc (< 6 %), aluminium-manganese (< 2 %),
aluminium-silicon (< 2 %), aluminium-magnesium (< 2 %).
b) Coated materials. Materials with electrodeposited or other coatings.
c) Cobalt and its alloys. Pure cobalt, hard facing alloys, corrosion-resistant alloys.
d) Copper and its alloys. Copper (unalloyed, phosphorus-bearing, silver-bearing), low alloyed copper
alloys (formerly designated as e.g. beryllium-copper, chromium-copper and others), copper-zinc
alloys (brasses), copper-tin alloys (tin-bronzes/ phosphor-bronzes, including some gunmetals),
copper-tin-lead alloys (including some gunmetals), copper-nickel-zinc alloys (nickel-silvers),
copper-nickel-alloys (cupro-nickel), copper-aluminium alloys (aluminium bronzes), copper-
manganese-aluminium alloys.
e) Ferrous metals. Cast iron, malleable iron, mild steel, carbon and low alloy steels, alloy steels, high
speed and tool steels, stainless, heat and corrosion-resistant steels.
f) Nickel and its alloys. Pure nickel, nickel-copper, nickel-iron, nickel-chromium-iron, nickel-
chromium.
g) Precious metals. Gold, platinum, palladium, silver and their alloys.
h) Refractory metals and alloys. Titanium, zirconium, tantalum, niobium and their alloys.
i) Tungsten and molybdenum. Tungsten, molybdenum, cemented carbides, silver–tungsten, copper-
tungsten.
j) Non-metallic materials. For example, ceramics, graphite, tungsten carbide, diamonds, cermets, glass,
sapphire.
5.1.2 Special considerations
5.1.2.1 General
Some of the parent materials listed in 5.1.1 may have their properties adversely affected by the brazing
process, either because of the effects of temperature or because of metallurgical interactions. In
addition, consideration needs to be given to the effects that may arise in the brazing of dissimilar
materials. Therefore, the points in 5.1.2.2 to 5.1.2.13 need to be considered when the brazing of such
materials is proposed.
5.1.2.2 Dissimilar parent materials
One advantage of brazing is that many combinations of parent materials can be joined, but the effects of
the brazing cycle on their physical and metallurgical characteristics always need to be considered.
The primary physical property to be considered is the coefficient of thermal expansion. This has two
main effects. The gap between the components at brazing temperature will not be the same as the
assembly gap (for which allowance has to be made in designing the joint). There may also be sufficient
residual stress after brazing to cause mechanical failure. Depending on the form of the joint, this can
cause severe distortion or even cracking, e.g. as sometimes occurs in the brazing of carbide tool tips to
shanks, and allowance can be made for this by using the appropriate filler form or joint design to
produce a thick compliant joint.
Metallurgical effects can influence the mechanical properties of the joint. In some cases brittle
compounds may be formed but in other cases the joint may be strengthened.
5.1.2.3 Effects of brazing process on parent material properties
Where an alloy to be brazed depends for its strength on work hardening, hardening will be minimized
by the brazing operation and this cannot be recovered. Precipitation hardenable alloys may be affected
by the brazing operation: it may be possible to recover any loss in strength by suitable heat treatment.
In some cases consideration needs to be given to changes in the corrosion properties caused by the
brazing process. Information should be sought from the parent material supplier about these effects.
5.1.2.4 Alloys with tenacious surface oxides
Parent alloys containing additions forming tenacious oxide films are more difficult to braze than parent
materials of the same system that do not. The most common additions are aluminium and titanium in
stainless steels and nickel alloys. Such parent material will require special attention both in respect of
surface preparation prior to brazing and the degree of protection provided by the flux or atmosphere
used during the process, e.g. special fluxes or atmospheres or plating before brazing.
5.1.2.5 Porous metals
Components produced by powder metallurgical processes which have connected porosity (less than
about 90 % of theoretical density) may prove difficult to braze because of capillary absorption of the
filler materials. Sealing of the surface prior to brazing will be necessary in such cases.
5.1.2.6 Metals and alloys containing reducible oxides
Metals or alloys containing oxide inclusions or dissolved oxygen, which are easily reduced at the
brazing temperature, shall not be brazed in a reducing atmosphere; the oxide inclusion can form steam
causing porosity and loss of ductility.
5.1.2.7 Aluminium alloys
The filler materials used for brazing aluminium and its alloys are normally based on the Al-Si system. If
the parent material contains magnesium as an addition, this reacts with the silicon in the brazing alloy
to form an intermetallic compound at the interface. If the level of magnesium is more than 2 %, the
amount of intermetallic compound at the interface may embrittle the joint.
5.1.2.8 Lead-bearing copper alloys
Lead is added to various copper alloys, e.g. to improve machinability, it being insoluble in copper and its
alloys. If above about 2 %, lead may interfere with brazing
a) by forming an non-wettable dross at the interface; and
b) by causing cracking.
These effects can be reduced by adequate fluxing and uniform heating without imposed stress.
5.1.2.9 Free machining carbon steels
Lead and sulphur are added to carbon steels to improve machinability. Lead additions below 0,35 % are
not considered to reduce brazeability or joint strength, but higher levels may result in low joint
strengths because of interaction with the filler material. When vacuum furnace brazing, it should be
noted that lead will volatize from the surface of the steel.
Sulphur-bearing free machining carbon steels, which typically contain up to 0,6 % sulphur, are readily
brazed. Joint strengths are comparable with sulphur-free grades.
5.1.2.10 Cast iron
Spheroidal graphite (s.g.) cast irons are fairly readily brazed with silver filler materials but flake
graphite irons are more troublesome because the flakes interfere with wetting. One remedy is special
surface treatments to remove the flakes, or an alternative may be to use a silver brazing filler material
containing nickel.
5.1.2.11 Reactive and refractory metals and their alloys
Titanium, zirconium, niobium and tantalum and their alloys are not normally brazed and specialist
advice should be sought before it is attempted. It is essential that an inert atmosphere is always used
(argon or vacuum) and that hydrogen-bearing atmospheres are never used.
Molybdenum and tungsten can be brazed in hydrogen as well as in inert atmospheres. However, it is
preferable that the brazing temperatures are below the recrystallization temperature, otherwise the
parent material can be severely embrittled.
5.1.2.12 Metals prone to cracking during brazing
The main cause of cracking is the stressing of components while in contact with molten filler material.
This stress may originate from work hardening of the parent material, from restraint imposed by a jig
or from uneven heating. The cracking occurs at grain boundaries which tend to fill with brazing filler
material. The phenomenon is sometimes called stress cracking or liquid metal penetration. To prevent
this, annealed material should be used where applicable, even heating should be ensured and jigs
designed to avoid restraint.
5.1.2.13 Non-metallic materials
Ceramics may be brazed either by previously metallizing the ceramic surface or by using reactive metal
filler materials.
For glass materials special glass filler materials are available.
5.2 Filler materials
5.2.1 General
The principal filler materials covered by this standard are those detailed in EN ISO 17672 and these fall
into the classes shown in Table 2. Other commercially available filler materials can be used provided
that they are acceptable to both the manufacturer and the user.
It is important that filler materials are stored and used under the conditions recommended by the
manufacturer.
Melting ranges of the main filler material classes are shown in Figure 6.
Annex C gives details of the filler materials most commonly used for combinations of parent materials.
Annex D gives a guide to the suitability of various brazing filler material classes for the commoner
brazing methods. Of necessity, it has been drawn up in very general terms. The suitability of the
combination has to be decided in each case.

Table 2 — EN ISO 17672 filler metals
EN
ISO 17672:2016 Class Composition
reference
Al Aluminium brazing filler metals
Ag Silver brazing filler metals
CuP Copper-phosphorus brazing filler metals
Cu Copper brazing filler metals
Table A.1
Ni Nickel brazing filler metals
Co Cobalt brazing filler metals
Pd Palladium bearing brazing filler metals
Au Gold bearing brazing filler metals
Special ‘vacuum application’ versions of certain Ag, Pd and Au brazing
Table 1
filler materials
Figure 6 — Melting range of main filler material groups (schematic)
5.2.2 Forms available
The normal forms available include rod, wire, foil, preforms, powder, paste and clad sheet. A few
brazing filler materials may also be sprayed, coated or vacuum deposited or blended from powders. The
forms in which the brazing filler material are available should be determined at the design stage.
5.2.3 Applications
5.2.3.1 General
The choice of filler material for brazing a given combination of parent materials depends upon many
factors, in some cases there will only be one possibility, in others, several. Not every filler material in a
class can be used in a specific case.
5.2.3.2 Class Al
The filler materials in this class are used almost exclusively for the joining of pure aluminium and a
restricted range of aluminium alloys.
5.2.3.3 Class Ag
Silver brazing filler materials find wide application in the brazing of materials given in 5.1 with the
exception of aluminium, magnesium and refractory metals and their alloys. Special grades are available
for vacuum applications.
5.2.3.4 Class CuP
These filler materials are usually restricted to joining copper and its alloys. With the exception of
CuP386, they are self-fluxing on copper, but a flux or protective atmosphere is required on most copper
alloys. These phosphorus-bearing filler materials are not normally used for joining steel or nickel alloys,
as brittle phases may be formed.
5.2.3.5 Class Cu
These filler materials are generally used for brazing copper, cemented carbide and ferrous components
(Cu4XX, Cu6XX and Cu7XX with a flux) and for brazing of ferrous and some other high melting parent
materials in a protective atmosphere or vacuum (Cu1XX and Cu9XX).
5.2.3.6 Class Ni and Co
These filler materials are used almost exclusively for joining stainless steel and other heat and
corrosion-resistant alloys in either vacuum or protective atmospheres.
5.2.3.7 Class Pd and Au
These filler materials are used in protective atmospheres or vacuum to join metallized ceramics, copper
alloys, nickel alloys and steels.
5.3 Fluxes
5.3.1 General
Fluxes are an essential requirement when brazing in air, with the general exception of the self-fluxing
copper-phosphorus filler materials. Fluxes are also an integral part of all flux bath processes. In some
circumstances they are used in protective atmosphere brazing operations.
The most commonly available forms are powder and paste. Alternatives include gases and liquids, flux-
coated or cored filler materials and flux/filler material mixtures.
Fluxes are generally applied prior to heating.
Fluxes for brazing shall be as standardized in EN 1045.
5.3.2 Flux removal
5.3.2.1 General
Some flux residues are chemically active and their complete removal is essential if undesirable
corrosion of the parent material is to be avoided.
The method of their removal will depend largely on the stage of exhaustion attained by the flux at the
completion of the brazing cycle. This will depend upon the use of an adequate amount of the
appropriate flux, avoidance of overheating and a heating time as short as possible. Provided that the
assembly can sustain such treatment without damage, flux removal may be facilitated by quenching the
assembly into water immediately after the brazing filler material has solidified.
Flux residues should be disposed of in accordance with the relevant regulations.
5.3.2.2 Fluxes for brazing ≥ 750 °C (e.g. FH21, FH30)
The fused residues from borax and similar high temperature fluxes are hard, glassy and relatively
insoluble in water. Therefore they have to be removed mechanically, e.g. by grit or shot blasting or
abrasive techniques.
5.3.2.3 Fluxes for brazing < 750 °C (e.g. FH10, FH11, FH12)
Residues from fluoroborate fluxes are relatively water soluble and may be removed in hot or boiling
water. The efficiency of flux removal may be improved by agitation or ultrasonic vibration. Chemical or
proprietary inhibited descaling solution may be used where complete removal of all residual
discoloration is required. Non-immersion methods which are equally effective include steam lancing
and wet or dry abrasive techniques.
5.3.2.4 Aluminium brazing fluxes
Type FL10 fluxes are highly corrosive and require very careful post-braze removal. The flux residues
are water soluble and can be washed away. Type FL20 fluxes are generally non-corrosive and the
residue can often be left in situ.
5.4 Atmospheres
5.4.1 Protective
Examples of types of protective atmosphere are listed in Table 3.
Users should understand that the effects of atmospheric purity, cycle time and temperature are
interrelated and will affect the requirements for satisfactory brazing. The function of a protective
atmosphere is to ensure the cleanliness of the parent and filler materials so that the latter can flow
freely during brazing.
The choice of atmosphere will be influenced by the parent and filler materials and may be active or
inert.
5.4.2 Vacuum atmospheres for brazing
A vacuum atmosphere is achieved in a vessel specifically designed for brazing or heat treatment by
pumping out the furnace gases, usually air. The pumps are generally a carefully designed combination
of mechanical and oil diffusion which are matched in pumping capacity, and of sufficient size to
evacuate rapidly the furnace space. Outgassing of the charge of components and the interior of the
furnace will occur during the heating cycle, and the pumps are frequently automatically interlocked
with vacuum measuring instruments to accommodate this.
–3
A vacuum of better than 10 mbar is easily achieved, but a low leak rate is equally important to control
–3 –6
the residual atmosphere. 10 mbar is equivalent to a gas impurity content of approximately 1,1 × 10
(parts per million) by volume.
5.5 Safety
The manufacturer's advice should be sought to ensure that the flux, atmospheres, filler material and
parent materials are compatible.
Table 3 — Examples of protective atmospheres
Typical Approximate composition Applications
dew point
of
H N CO
No. Source CO
2 2 2 Filler metal
incoming
Parent materials
class
gas
°C % % % %
a
1 Combusted Up to +30 1 to 5 87 1 to 5 11 to Ag , CuP, Cu and some Cu alloys. Low
d
a a
fuel gas 12 and medium carbon steels
Cu4XX Cu6XX
a
(low
Cu7XX
hydrogen)
a
2 Combusted Up to +30 14 to 70 to 9 to 10 5 to 6 Ag ,CuP, Cu and some Cu alloys, low
d
fuel gas 15 71 Cu1XX, Cu9XX and medium C steel, Ni, Ni-Cu
a a
(decarburizi Cu4XX Cu6XX alloy
a
ng) Cu7XX
a
3 Combusted –40 15 to 73 to 10 to – Ag ,CuP, Cu and some Cu alloys,
f
fuel gas , 16 75 11 Cu1XX, Cu9XX, carbon steels, Ni-Cu alloy, Ni,
a a
dried Cu4XX Cu6XX Ni-Fe alloys
a
Cu7XX
a
4 Combusted –40 38 to 41 to 17 to – Ag ,CuP, Cu and some Cu alloys,
e a
fuel gas , 40 45 19 Cu1XX, Cu4XX carbon steels, Ni-Cu alloy, Ni
a a
dried Cu6XX Cu7XX
(carburizing)
5 Dissociated –54 75 25 – – Ag, CuP Cu1XX, Cu and some Cu alloys,
g
ammonia Cu9XX, Cu4XX carbon steels, Ni-Cu alloy, Ni
(cracked Cu6XX Cu7XX, and Ni alloys, alloys
b
Ni106, Ni107
ammonia) containing Cr
6 Cylinder Down to 100 d – – Ag, CuP, Cu1XX, Cu and some Cu alloys, low
hydrogen –60 Cu9XX, Cu4XX and medium carbon steels, Ni
Cu6XX Cu7XX, and Ni alloys and alloys of Co,
b
Ni107 Cr and cemented carbides
7 Inert gasg, Below –60 – – – – CuP,Cu1XX, Cu and some Cu alloys,
e.g. argon, Cu9XX, Ni carbon steels, Ni and Ni
c b
nitrogen alloys , alloys containing Cr
a
Flux additionally required when filler materials containing volatile elements are used.
b
Flux required in addition to atmosphere when appreciable quantities of aluminium, titanium, silicon or beryllium are
present.
c
It is essential that nitrogen is not used with refractory metals or aluminium or when the filler material contains boron or
silicon.
d
The combusted fuel gas (low hydrogen or decarburizing) may be referred to as exothermic. It may also be available as
synthetic gas.
e
The combustable fuel gas (carburizing) may be referred to as endothermic. It may also be available as synthetic gas.
f
It may also be available as synthetic gas.
g
Certain filler materials in EN ISO 17672:2016, Tables 7 and 8, can be brazed in protective atmospheres 5 and 7.

6 Methods of brazing
Annex E gives details of the different method of brazing, including the advantages and limitations of
each method.
7 Heat treatment
Where the parent materials require heat treatment, it may be possible to carry this out as part of the
brazing operation. In other cases it will be necessary to carry out heat treatment separately. If the
subsequent heat treatment requires quenching, there is a risk of distortion and/or cracking.
8 Inspection
Where applicable, brazer qualification in accordance with EN ISO 13585, brazing procedure
qualification in accordance with EN 13134, non-destructive testing of brazed joints in a
...