Brazing-copper:

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Copper Brazing Solutions

Brazing-copper and most of the copper alloys is described as easy and practical.

That is because these materials, except possibly for a few exceptions, are readily brazeable.

Attention, as always, has to be paid to select suitable process and filler metal to prevent possible problems.

The influence of brazing heat on base metal microstructure should be assessed.

It must be determined if any effects like annealing are desirable or not.

In previous pages of this Website we dealt with Brazing in general, with Brazing Joint Design, and with Brazing Heating that describes the different methods of heating for brazing.

Brazing-copper Base Metals

Problems are found when trying Brazing-copper when tough pitch copper containing oxygen is used, in hydrogen based furnace atmospheres, because high pressure steam is formed in the solid metal with destructive results. Also torch brazing of tough pitch copper should be avoided as it may produce embrittlement.

Deoxidized coppers are readily brazed, even without flux in protective atmospheres if Brazing-copper phosphorous filler metal is used, because phosphorus is a powerful deoxidizer. However the use of flux is generally recommended because it improves the process.

Copper alloys containing chromium or aluminum must be thoroughly cleaned to remove oxides that interfere with brazing. Furthermore the use of special AWS flux type FB4-A is recommended.

Fluxes are used to braze brasses which are alloys of copper and from 5 to 40% zinc. Overheating or heating brasses for too long may leave voids because zinc tends to vaporize.

Bronzes were originally alloys of copper and tin. Modifications were introduced that conserved the name even if tin content was reduced or eliminated. Most important categories now include phosphor-bronze, silicon-bronze and aluminum bronze.

Phosphor-bronze alloys should be brazed only after stress relieving
at 290 to 345 °C (550 to 650 °F), because in cold worked condition they are prone to hot cracking.

These are important considerations to remember when approaching Brazing-copper of particular copper alloys.

Filler Metals

ANSI/AWS A5.8M/A5.8:2011
Specification for Filler Metals for Brazing and Braze Welding
Edition: 10th
American Welding Society / 17-Jun-2011 / 62 pages

ISO 3677
Filler metal for soft soldering, brazing and braze welding - Designation
International Organization for Standardization, 01-Jun-1992, 2 pages

Brazing-copper with copper base filler metals is commonly done, one has just to take care of a few precautions depending on the type of base metal. A few recommendations can be found in Issue 34 of Practical Welding Letter for June 2006.

A Table of some Copper Base brazing filler metals by their AWS classification is shown hereafter:

Table
Copper Base Brazing Filler Metals
AWS A5.8 Composition % Temperature C/F
Class Cu Zn P Ag Ni Other Solidus Liquidus
BCu-1 99.9 - 0.075 - - Pb=0.02 1080/1980 1080/1980
BCu-1a 99.0 - - - - 0.30 1080/1980 1080/1980
BCu-2 99.0 - - - - 0.30 1080/1980 1080/1980
RBCuZn-A 59.25 40 - - - Sn=0.75 890/1630 900/1650
RBCuZn-D 48 42 - - 10 - 920/1690 935/1715
BCuP-1 95 - 5 - - - 710/1310 900/1650
BCuP-2 92.75 - 7.25 - - - 710/1310 795/1460
BCuP-4 86.75 - 7.25 6 - - 645/1190 725/1335
BCuP-5 80 - 5 15 - - 645/1190 800/1470

A Table listing copper base brazing alloys can be found also in a commercial publication. See Filler Copper Alloys .

Brazing-copper with silver base filler metals is also very popular. A few indications and a Table of some wires and rods by their AWS classification can be found in Issue 3 of Practical Welding Letter for November 2003. Click PWL#03

Brazing-copper can also be performed with precious metal base filler metals, in particular with a gold alloy named BAu-4 containing 82% Au and 18% Ni, but its use is limited to high cost applications for vacuum and electronic devices where low vapor pressure is important.

Fluxes

Apart from the special flux mentioned above (type FB4-A) to be used for removing tough oxides generated by the presence in the base metal of chromium or aluminum, other fluxes are available commercially.

Their ingredients, generally borates, fluorides and chlorides, are selected for their activity at definite temperatures corresponding to the brazing temperature range of the different filler metals. Suppliers recommendations may refer also to the base metals.

Fluxes for Brazing-copper are supplied as powders or slurries, but also as liquids for special applications. Torch brazing is sometimes performed by having the fuel gas pass through a container containing liquid flux.

Brazing-copper

All the methods described in our page on Brazing Heating can be used, the selection being generally determined by expediency and economy, provided the requirements of the final product are met satisfactorily.

Furnace brazing is the process whose main advantage is its adaptability to mass production of repetitive brazed units. Furnaces must be adequate to manage the required mass with suitable atmosphere and temperature controls.

Brass is not furnace brazed, generally. Gases containing sulfur should not come in contact with copper or copper alloys.

ANSI/AWS A5.31M/A5.31:2012
Specification for Fluxes for Brazing and Braze Welding
Edition: 2nd
American Welding Society / 17-Feb-2012 / 38 pages

ANSI/AWS D10.13/D10.13M:2001
Recommended Practices for the Brazing of Copper Pipe and Tubing for Medical Gas Systems
American Welding Society, 01-Jan-2001, 21 pages

The Copper Development Association Inc. makes available to anybody upon request a hardcopy leaflet presenting examples of Qualification documents:
Brazing Procedure Specification (BPS)
Procedure Qualification Record (PQR)
Brazing Performance Qualification Record (BQR)
discussing the requirements of NFPA and referring to the ASME and to AWS Specifications. Whoever is involved with this kind of production (Brazing of Copper Tubing and Copper Alloy Fittings) is urged to contact CDA and request the document.

Brazing Procedure Specifications.

Resources

Easily select Brazing Outfits you may need.
Click on the Welding Advisers Store.


A note on Furnace Brazing Copper was published (3) on Issue 99 of Practical Welding Letter for November 2011.
Click on PWL#099 to see it.

An Article on Filler Metal for brazing copper or steel to titanium was published (4) in Issue 133 of Practical Welding Letter for September 2014.
Click on PWL#133 to see it.

An Article on Controlled-Atmosphere Induction Brazing was published (7) in Issue 136 of Practical Welding Letter for December 2014.
Click on PWL#136 to see it.

An Article on Filler Metal for brazing a copper cable to a copper rivet was published (4) in Issue 137 of Practical Welding Letter for January 2015.
Click on PWL#137 to see it.

An Article on Silver-Free Brazing Filler Metals Meet Strength Requirements was published (4) in Issue 148 of Practical Welding Letter for December 2015.
Click on PWL#148.

An Article on Brazing Filler Metal Alloys was published (4) in Issue 166 of Practical Welding Letter for June 2017.
Click on PWL#166.

1. - Articles:

An article from the AWS Welding Journal of August 2002 on Tips for Soldering and Brazing Copper Tubing can be found at
http://www.aws.org/w/s/wj/2002/08/feature2

An article from The Fabricator of May 15, 2003 on Brazing copper tubing can be found at
Brazing copper tubing.

An article from Practical Welding Today of March 13, 2007 on Brazing-copper and copper alloys can be found at
Brazing.

An Article from International Copper Association, Ltd.
Manufacturers Discover Brazing Is Better for Joining Copper to Brass
www.kellenpr.com/clientnews/pdf/CuproBraze_34.pdf

2. - Information from Commercial Sources:

From Handy & Harman

on Fluxes
A Flux for every Need.

on Copper & Copper Alloys:
Brazing Materials Selection Chart.

From Aufhauser
http://www.brazing.com/products/Phos_Copper/
http://www.brazing.com/products/Braze_Copper/

Watch the following CDA Video on

Braze Copper Tube

http://www.youtube.com/watch?v=07ODV2Bdqow

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