Principles of brazing technology - technicalmaterials.umicore.com

Principles of brazing technology 

Brazing is a thermal process for securely joining and 

coating materials, whereby a liquid phase is 

produced by melting a brazing alloy (fusion-brazing) 

or by diffusion at the interfaces (diffusion-brazing). 

The solidus temperature of the base material is not 

reached (DIN 8505, Part 1). 

1. Standards and regulations for brazing 

1.1 Recommendations for brazing 

- Technical information sheets 

- Standards 

Technical information sheets: Recommended 

These are prepared by experts in work groups and 

the information corresponds to the respective state of 

technology. It is recommended that the technical 

information sheets be heeded as they are also 

viewed as the respective state of the technology from 

a legal point of view. 

Examples: 

- DVS-Guideline 1183: DVS-course „Brazing 

copper materials“ 

- VdTÜV – Technical Information Sheet 1160: 

„Evaluation of processes for manufacturing 

brazed joints and high temperature brazed 

joints“ 

- DVGW – Work Sheet GW2 

Standards: Compulsory 

Any deviation from the standard must be specifically 

agreed between the client and contractor. There are 

currently many national (DIN), european (EN) and 

international (ISO) standards. The existing German 

standards are being superseded by European 

standards. Referral is made in particular here to DIN 

EN 1044 „Brazing – composition of brazing 

alloys“ which replaces DIN 8513 Parts 1-5 and to 

DIN EN 1045 „Brazing – fluxes for brazing“ which 

replaces DIN 8511-1. Both these standards 

categorise the respective materials. There are also 

standards in existence which cover the terms used in 

brazing, constructional aspects, testing of brazed 

joints, inspecting brazed joints, etc. which can be 

obtained via Beuth-Verlag (Berlin) or DVS-Verlag 

(Düsseldorf). 

1.2 Regulations for work safety and accident 

prevention, e.g.: 

- Accident prevention regulations, section 15: 

„Welding and related techniques “ d.BG; 

- VDI 2046 „Safety guidelines for operating 

industrial furnaces with inert gas and reactive 

atmospheres“ 

2. Wetting process and capillary forces 

2.1 Distinction between welding and brazing 

In welding not only is the added alloy material melted 

but the base material is also partially melted. 

In brazing only the added brazing alloy melts. The 

base material is wetted in its solid state by the liquid 

brazing alloy. 

Fusion welding Brazing 

Usually similar materials Virtually any desired material 

combinations 

Virtually identical melting Brazing alloy melts at 

temperatures for the base lower temperature 

material and alloy than the base material 

2.2 Wetting 

A prerequisite for brazing is the wetting of the base 

material by the brazing alloy. Three important 

conditions must be fulfilled for this to happen: 

• the brazing surfaces and the brazing alloy must 

be „bare metal“, 

• the brazing surfaces and the brazing alloy must 

have at least reached the working temperature, 

• at least one component of the brazing alloy must 

readily form an alloy with the base material. 

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Base material 

- Visible oxide layers (rust and scale), fat layers 

and layers of dirt must be removed before 

carrying out brazing work. Thin oxide layers (e.g. 

tarnishing) may remain on the workpieces if 

brazing is carried out using a flux. 

- The working temperature is the lowest surface 

temperature of a workpiece at the brazing joint at 

which the brazing alloy can wet, spread and bond 

with the base material. This temperature is always 

higher than the solidus temperature of the brazing 

alloy. It can be above, below or the same as its 

liquidus temperature. 

- The wetting process involves surface alloying 

between the brazing alloy and the base material. 

Next to the wetting zone there is a diffusion zone 

which is very small for brazing work and cannot 

be detected by metallographic means. In order to 

attain optimum strength, the brazing alloy must be 

liquid for at least 8 to 10 seconds to give an 

adequately deep diffusion zone. 

There is greater interaction between the brazing alloy 

and base material when carrying out high 

temperature brazing (flux-free brazing at 

temperatures above 900°C in a controlled 

atmosphere). 

2.3 Joint-brazing and gap-brazing 

Joint-brazing is a brazing technique similar to gasfusion 

welding from a joint preparation and working 

method point of view. It is virtually always carried out 

manually. The working temperature of the brazing 

alloy must not be exceeded when joint-brazing. 

1 to 1.5 mm 

The most important area of application of jointbrazing 

is for brazing galvanised steel pipes. 

The workpieces are prepared for gap-brazing such 

that the brazing joints are narrow capillary gaps. 

They are heated up to brazing temperature uniformly 

over the whole length of the gap. The liquid brazing 

alloy is forced into the gap by „capillary filling 

pressure“. This technique is easy to mechanise. The 

majority of brazing work is carried out by the gapbrazing 

technique. 

The surface forces are additive in the narrow 

capillary gaps (size of the order of 0.1 mm), so that 

the brazing alloy is preferentially drawn into the 

narrow gap. If brazing is being carried out with a flux 

in a gas atmosphere, the brazing alloy which 

penetrates into the brazing gap must be able to push 

the flux out of the gap. 

In gap-brazing, the working temperature of the 

brazing alloy may be exceeded – by in general 20 to 

50°C. 




Start of the wetting Intermediate state 

II = Workpiece 1 

II = Workpiece 2 

Both bare metal, and 

heated to working 

temperature 

• Liquid brazing alloy 

Capillary filling pressure 

Final state 

The brazing alloy is pressed into the gap by capillary 

forces. The narrower the brazing gap, the higher the 

capillary filling pressure. 

For a 0.1 mm parallel gap, the capillary filling 

pressure reaches ca. 100 mbar, corresponding to 

about 0.1 Atm. This in turn corresponds to about a 1 

m column of water ( ρ = 1); assuming ρ = 10 g/cm 3 

(the density of a brazing alloy), the capillary height 

for low melting point brazing alloys in a 0.1 mm wide 

gap can be calculated to be ca. 10 cm. This agrees 

reasonably well with experiences in practice. 

Gap too narrow 

Correct gap width 

(only applies for 

brazing with flux) 

Permissible gap width for manual brazing 

Gap too wide 

Different gap cross-sections give different filling 

pressures. An open fillet has a six times higher 

capillary filling pressure than a parallel flat gap. 

3. Brazing alloy and flux groups 

3.1 Brazing alloys 

According to DIN 8505, alloys with a liquidus 

temperature below 450°C are solders and those with 

a liquidus temperature above 450°C are brazing 

alloys. 

The upper and lower brazing temperature limits are 

determined by the following: 

lower limit 

- the working temperature 

upper limit 

- the flux (becomes saturated with oxides at 

too high temperatures), or 

- the brazing alloy (individual components of 

the alloy can evaporate), or 

- the economics of the process (unnecessarily 

high temperatures cost unnecessary time 

and energy), or 

- the base material (structural transformation; 

strength loss). 




3.2 Fluxes 

Fluxes are solvents for metal oxides. They have an 

effective temperature range within which they are 

able to dissolve metal oxides. The solvating capacity 

of the flux is limited. About 5% of the weight of flux in 

metal oxides can be dissolved. If oxides are present 

in greater amounts, the flux saturates and it loses its 

functionality. 

Atmospheric 

oxygene Flux Oxide 

More than 5 min. 

The hygroscopic flux residues must be removed by 

scouring in water or by pickling in pickling baths 

suitable for the base materials. Ultrasound aids the 

removal of these flux residues. 

The non-hygroscopic flux residues do not have to be 

removed for fear of corrosion. If they need to be 

removed for other reasons (e.g. to paint the 

components), they are usually removed by 

mechanical means (e.g. sand-blasting). 

Too little Sufficient 

Oxide film remains Oxide film is 

dissolved 

The solvating capacity of modern brazing fluxes for 

use at low temperatures (i.e. between 600 and 

800°C) for common heavy metal oxides is between 1 

and 5%, meaning that it is limited. That means that 

relative to the oxide which is present a relatively 

large amount of flux must be available, and ultimately 

so in the molten state, otherwise sound brazing work 

is not achieved. Extremely narrow gaps, e.g. less 

than 0.02 mm, hence cause problems because there 

is an inadequate amount of flux in the gap. This 

naturally has a big effect on the soundness of the 

brazed joint. 

Wire of brazing alloy 


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Flux 

For surface brazing, the high capillary filling pressure 

in the open fillets leads to running of the brazing alloy 

on the external sides. The supply of brazing alloy to 

the narrow surface gap is reduced; increased 

inclusion of flux hence occurs. 

Brazing alloy 

Flux 

Increased flux inclusion can be avoided by inserted 

brazing alloy sheet. 

Gaseous fluxes 

Joints (V-seams and fillets) can be brazed using 

gaseous fluxes. For brazing gaps – especially for 

gaps having larger depths and small widths – the use 

of gaseous fluxes is not recommended because the 

flame does not penetrate into the capillary gap. 

When using flux pastes, their working life can be 

significantly prolonged by the additional use of 

gaseous fluxes. 

The effective temperature of gaseous fluxes extends 

from about 750°C to 1100°C.


Brazing with flux-forming brazing rods - BrazeTec 

Silfos brazing alloys. 

Oxygen 

Fuel gas 

Copper alloys, copper-tin alloys and silver can be 

brazed with phosphorus-containing brazing alloys 

without the use of flux. The „self-flowing“ properties 

of these brazing alloys can be explained as follows: 

On melting the brazing alloy, the phosphorus in the 

brazing alloy reacts with oxygen in the air to form 

phosphorus pentoxide. This reacts with the copper 

protoxide on the copper surface to form copper 

metaphosphate which acts as a flux. As copper 

metaphosphate is safe from a chemical- corrosion 

point of view, the brazed joints require no 

subsequent treatment. 

When brazing with BrazeTec Silfos brazing alloys, 

the brazing time should not be longer than about 3 to 

4 minutes. 

4. Brazability of components 

According to DIN 8514, the brazability is the property 

of a component to be manufactured in such a way 

via brazing that it meets the stipulated requirements. 

A component can be brazed if the following 

conditions are met (see diagram): 

- the base material is suitable for brazing, 

- there is a brazing capability for the 

manufacture, namely one or more brazing 

techniques can be used, 

- and the construction can be brazed such that 

a sound construction results, namely 

satisfactory reliability of the component 

under the foreseen operating conditions. 

Comment: In electrical engineering, the expressions 

„solderability“ and „suitability for soldering“ are used 

synonymously for soldering. 

Soundness of 

the brazed joint 

Construction 

Base material 

Suitability for 

brazing 

Brazability 

of the 

component 

Suitable base material, brazing alloy and flux 

combinations 

Each of the three properties „suitability for brazing“, 

„brazing capability“ and „ability to manufacture a 

sound brazed joint“ depend on the base material, 

manufacturing process and joint design. The degree 

of dependency on these three parameters depends 

on the individual brazing task. 



Brazing 

capability 

Manufacture


The suitability of base materials for brazing work is 

shown in Table 1. 

Tables 1 and 3 give information about how the 

indicated materials can be brazed. This does not 

mean to say that components brazed in this way can 

withstand all operating loads. In order to guarantee 

this, the operating conditions for the brazed joints 

must be known prior to selecting the 

conditions/methods for carrying out the brazing work. 

These are workpiece-specific and differ from one 

component to the next. More detailed information on 

Suitability of base materials for brazing 

this matter can be found in the section entitled 

„Selection criteria for brazing alloys and fluxes“. In 

certain instances where there is relatively high risk of 

damage, we recommend that you get in touch with 

us to enable optimum selection of the brazing 

parameters. 

Brazing has the big advantage that virtually all 

materials which are suitable for brazing can be 

combined with each other. It goes without saying that 

the brazing parameters must always be selected for 

the most „difficult“ material from a brazing point of 

view. 

Group 1 Group 2 Group 3 

Materials which can be brazed with 

universal brazing alloys and universal 

fluxes and using all standard 

techniques. 

e.g. 

copper and copper alloys 

nickel and nickel alloys 

iron materials 

common steels 

cobalt 

noble metals 

Table 1 

Materials which require special 

brazing alloys and/or special fluxes, 

but which do not require special 

brazing techniques. 

e.g. 

aluminium and aluminium alloys 

hard metals, stellites 

chromium, molybdenum, tungsten, 

tantalum, niobium 

solder-like materials 

Materials which can only be 

brazed using special brazing 

alloys and special techniques. 

e.g. 

titanium 

zirconium 

beryllium 

ceramics 




Solder and brazing alloy groups (I) 

Group description Soldering / 


temperature 

range 

°C 

Tin-lead solders 

EN 29453 

Special solders 

EN 29453 

Cadmium-free 

universal brazing 

alloys 

DIN EN 1044 

(DIN 8513) 

Low melting point 

cadmiumcontaining 

universal 

brazing alloys 

DIN EN 1044 

(DIN 8513) 

Typical solders / 

brazing alloys in this 

group in accordance 

with EN (DIN) 

145 ... 325 S-Sn60Pb40 

S-Pb50Sn50 

145 ... 395 S-Sn97Cu 3 

650 ... 1100 

S-Sn96Ag4 

S-Sn96Ag3 

S-Sn95Sb5 

AG 104 (L-Ag45Sn) 

AG 106 (L-Ag34Sn) 

AG 203 (L-Ag44) 

AG 207 (L-Ag12) 

CU 303 (L-CuZn40) 

CU 102 (L-Cu) 

610 ... 800 AG 304 (L-Ag40Cd) 

AG 306 (L-Ag30Cd) 

Manganesecontaining 

special 


DIN EN 1044 

(DIN 8513) 

690 ... 1020 AG 502 (L-Ag49) 

1) not laid down in standards 

Table 2a 

BrazeTec name Solidus 

temp. 

Soldamoll 230 

(BrazeTec 3) 

Soldamoll 220 

BrazeTec 4 

Soldamoll 235 

BrazeTec 4576 

BrazeTec 3476 

BrazeTec 4404 

BrazeTec 1204 

BrazeTec 60/40 

BrazeTec 4003 

BrazeTec 3003 

BrazeTec 4900 




°C 

183 

183 

230 

221 

640 

630 

675 

800 

875 

1083 

595 

600 

680 

980 

Liquidus 

temp. 

°C 

190 

215 

250 

221 

240 

680 

730 

735 

830 

895 

1083 

630 

690 

705 

1030 

Max. permissible 

continuous 

operating 

temperature 1) 

°C 

80 

80 

110 

110 

110 

200 

200 

300 

300 

350 

150 

150 

400 

600 

Most important 

areas of application 

Electro-industry 

Copper pipe installation for 

hot and cold water systems 

Food industry 

Refrigeration engineering 

Gas and water installation 

Gas and water installation 

Electrical engineering 

Galvanised steel pipes, steel 

furniture 

Inert gas brazing of mass- 

produced components 

Electrical engineering 

Refrigeration engineering 

Car-suppliers-industry 

Hard metal tools 

Hard metal tools


Solder and brazing alloy groups (II) 

Group description Soldering / 


temperature 

range 

Phosphoruscontaining 


alloys for copper 

base materials 

DIN EN 1044 

(DIN 8513) 

Special brazing 

alloys for special 

brazing work 

DIN EN 1044 

(DIN 8513) 

High temperature 

nickel-based 


DIN EN 1044 

(DIN 8513) 

Aluminium brazing 

alloys 

DIN EN 1044 

(DIN 8513) 

Table 2b 

Typical solders / 

brazing alloys in this 

group in accordance 

with EN (DIN) 

°C 

710 ... 800 CP 102 (L-Ag15P) 

CP 105 (L-Ag2P) 

CP 203 (L-CuP6) 

730 ... 960 AG 403 (L-Ag56InNi) 

900 ... 1200 

Ni 107 (L-Ni7) 

Ni 105 (L-Ni5) 

Ni 102 (L-Ni2) 

560 ... 600 AL 104 (L-AlSi12) 

BrazeTec name Solidus 

temp. 

BrazeTec Silfos 15 



BrazeTec 5603 

BrazeTec 6009 

BrazeTec 7200 

BrazeTec 897 

BrazeTec 1135 

BrazeTec 1002 




645 

°C 

645 

710 

600 

600 

780 

890 

1080 

970 

575 

Liquidus 

temp. 

800 

°C 

825 

890 

710 

720 

780 

890 

1135 

1000 

590 

Max. permissible 

continuous 

operating 

temperature 2) 

°C 

150 

150 

150 

200 

200 

300 

200 

Most important 

areas of application 

Electro-industry 

Copper pipe installation for 

sewer gas / natural gas 

High grade steel 

High grade steel 

Vacuum technology 

Core and reactor constr. 

Turbine construction 

Turbine construction 

Heat exchangers


Flux groups (I) for soldering/brazing metallic materials 

Flux group Flux type Information about the manufacture Most important areas of application Nature of flux residues 

3.2.2. Zinc chloride and/or ammonium Chromium-containing steels; 

chloride and free acids 

highly oxidised workpieces 

3.1.1. Zinc chloride and/or ammonium Chromium-free steels and non-noble metals, if 

Corrosive 

chloride 

washing off the residues is possible 

Fluxes for 

soldering heavy 

metals 

DIN EN 29454 

Fluxes for 

soldering light 

metals 

DIN EN 29454 

Table 3a 

3.1.1. 

2.1.3 

2.1.1 

2.1.2. 

1.1.2. 

1.1.1. 

1.1.3. 

3.1.1. 

2.1.3. 

2.1.2. 

Zinc chloride and ammonium 

chloride in organic formulation 

Organic acids 

Amines, diamines, urea 

Organic halogen compounds 

Resins with halogen-containing 

activators 

Resins without additives 

Resins with 

halogen-free additives 

Solder-forming zinc chlorides 

and/or tin chlorides; 

also with additives 

Organic compounds 

Organic halogen compounds 

Chromium-free steels and non-noble metals, if 

washing off the flux residues is not possible 

Copper 

For workpieces which can be washed 



Partly corrosive 

Non-corrosive 

Corrosive


Flux groups (II) 

Flux group Flux type Information about the 

manufacture 

Fluxes for brazing FH10 Boron compounds and fluorides 

heavy metals FH11 

DIN EN 1045 FH12 

Fluxes for brazing 

light metals 

DIN EN 1045 

Table 3b 

FH20 

FH21 

FH30 

FH 40 

FL10 

FL20 

Boron compounds 

Boron compounds, phosphates, 

silicates 

Chlorides and fluorides 

Hygroscopic chlorides and 

fluorides 

Non-hygroscopic fluorides 

Most important areas of application Behaviour of the flux residues 

Silver brazing alloys with working temperatures up to 

ca. 800°C 

Brazing alloys with working temperatures between 

750 and ca. 1000°C 

Brazing alloys with working temperatures above 

1000°C 

Brazing alloys with working temperatures between 

600 and 1000°C for reactor construction (boron-free) 

For workpieces which can be washed (also pickled, 

neutralised) 

Heat exchangers 



Hygroscopic 

Non-hygroscopic 

Non-hygroscopic 

Hygroscopic 

Corrosive 

Non-corrosive


Proposals (I) for brazing alloy (solder) / flux / brazing (soldering) technique combinations (for Group 1 base materials in accordance with Table 3) 

Base material Brazing alloy Flux Technique *) Solder Flux Technique *) 

Cu CP 105 (L-Ag2P) 

- 

FL / Ind. 

S-Sn97Cu3 3.1.1. 

FL / EL.-W. 

CP 203(L-CuP6) 

- EL.-W / SO / VO S-SnAg4 

1.1.1. 

Cu-alloys CP 105 (L-Ag2P) 

AG 102 (L-Ag55Sn) 

AG 203 (L-Ag44) 

FH10 

S-Pb50Sn50 

Ni + Ni-alloys AG 102 (L-Ag55Sn) FH10 FL / Ind / EL.-W. / AO S-Pb50Sn50 3.1.1. FL / EL.- W. / Ind. 

Iron materials AG 203 (L-Ag44) 

SO / VO 

S-Sn96Ag4 

Common steels AG 304 (L-Ag40Cd) 

S-Sn97Cu3 

Cobalt 

CU 303 (L-CuZn40) 

CU 305 (L-CuNi10Zn42) 

FH20 

S-Cd82Zn16Ag2 3.1.1. HL / AO / FL / Ind. 

CU 102 (L-Cu) - 

Cr- and Cr/Ni-steels AG 403 (L-Ag56InNi) FH12 FL / Ind. / EL.-W. S-Sn96Ag4 3.2.2. FL / EL.-W./ K 

HL / AO 

NI107/NI105/NI102 

AG 401/CU102 

- SO / VO 

Noble metals AG 102 (L-Ag55Sn) FH10 FL / Ind. 

S-Sn96Ag4 3.1.1. 

AG 202 (L-Ag60) 

EL.-W. 

AG 401 (L-Ag72) 

AO 

Gold brazing alloys 

SO / VO 

*) FL = Flame; EL.-W. = Electr. Res.; SO = Inert gas furnace; K = Copper-bit; Ind. = Induction; AO = Atmosphere furnace; VO = Vacuum furnace; 

HL = Hot air jet 

Table 4a 




Proposals (II) for brazing alloy (solder) / flux / brazing (soldering) technique combinations (for Group 2 and 3 base materials in accordance with 

Table 3) 

Base material Brazing alloy Flux Technique *) Solder Flux Technique *) 

Al and Al-alloys AL 104 (L-AlSi12) FL10 FL 

S-Sn96Ag4 3.1.1. FL / (K) 

(with Mg and/or 

Si contents ≤ 2%) 

AO 

S-Cd80Zn20 

Hard metals AG 301 (L-Ag50CdNi) FH12 

FL 

- 

- 

- 

AG 502 (L-Ag49), possibly 

as layer brazing alloy 

Ind. 

Stellites 

AG 502 (L-Ag49) FH12 

- 

- 

- 

CU 305 (L-CuNi10Zn42) FH21 

SO / VO 

CU 102 (L-Cu), possibly 

with tri-metal 

- 

Chromium, 

molybdenum, 

AG 502 (L-Ag49) FH12 

Tungsten, tantalum, 

niobium 

Cu87MnCo 1 FL/Ind. 

- - - 

) FH21 

AO/SO 

Zinc 

- - - S-Pb60Sn40 3.1.1. FL/EL.-W. 

Antimony 

S-Sn96Ag4 

K/HL 

Lead 

- - - 

Bismuth 

S-Sn50Pb32Cd18 3.1.1. 

FL/EL..-W. 

Tin 

K/HL 

Titanium 

AG 401 (L-Ag72) 

- SO (Argon) 

- - - 

PD 105 

VO 

Zirconium 

PD 105 - SO (Argon) 

- - - 

Beryllium 

VO 

Graphite 

AgCuTik 

Metal oxideceramics 

1 ) - SO (Argon) 

- - - 

VO 

*) FL = Flame; EL.-W. = Electr. Res.; SO = Inert gas furnace; K = Copper-bit; Ind. = Induction; AO = Atmosphere furnace; VO = Vacuum furnace; 

HL = Hot air jet 1 ) not laid down in standards 

Table 4b 




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equipment, plants and processes is based on 

extensive research work and our technical 

knowledge of applications. We provide this 

information verbally and in writing according to the 

best of our knowledge, but we do not accept any 

responsibility beyond that in the individual contract. 

We do however reserve the right to make technical 

changes as part of our product development 

activities. Our technical service personnel are 

available on request to provide further advice and 

assistance to solve manufacturing and technical 

problems. 

This does however not relinquish users of their 

responsibility to check our information and 

recommendations prior to carrying out their own 

work. This is also true – especially for deliveries 

abroad – with regard to the observance of protection 

rights of third parties and with regard to applications 

and procedures not expressly given in writing by us. 

In the event of damage, our liability is limited to 

compensation to the same degree as provided for in 

our General Terms and Conditions of Sale and 

Delivery for shortcomings in quality. 

BrazeTec GmbH, Rodenbacher Chaussee 4, D-63457 Hanau-Wolfgang 

Telefon: +49 (0) 6181-59-03 Telefax: +49 (0) 6181-59-55 50 Email: info@BrazeTec.de Internet: www.BrazeTec.de

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