Dip Brazing Aluminum 1

[eemotor]

Hello All,
I have an aluminum (6061) disk with slots cut into it. Aluminum fins (also 6061) will be inserted into the slots and joined using dip brazing. As far as I know, dip brazing process involves a bath of sodium, potassium, lithium and aluminum. Has anyone ever heard of using silver in the brazing process of aluminum? If so, how common is that? I know silver is used in brazing of copper and copper alloys but I don't think it's used with aluminum.

 

[tomwalz]

Try Lucas Milhaupt or Prince & Izant - both suppliers - both good for technical help - don't ask for sales - tell them you have a strange technical question

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessor.com

 

[Goahead]

Silver brazing alloys are not considered for brazing aluminum alloys. For one thing their melting range is too close or even overlapping that of the aluminum alloys.
As an example 6061 is reported with melting range of 1100 to 1200 F (593 to 649 C).
The lowest solidus point of common Silver brazing alloys is reported as 1125 F (605 C).
For dip brazing one common filler product is a brazing sheet, consisting in a layer of aluminum silicon alloy foil roll bonded to sheets of structural aluminum alloy.
Fluxes are generally of proprietary compositions but they should be periodically maintained with additions of fluorides and chlorides, and controlled for water and heavy metal content. Periodic additions have to be performed for compensating drag-out.

http://www.welding-advisers.com/

 

[eemotor]

It struck me as being a bit strange when another engineer suggested the use of silver brazing with aluminum. I didn't check the actual melting points of the alloys but I know that Aluminum melts at approximately 660 C while Silver melts at about 1080 C. So it didn't appear correct to me that one would try to braze aluminum with silver compounds based on the temperature. I hope this makes sense, any additional input is welcome.

 

[metman]

eemotor: As you have noted, the melting temperature of Ag is well above that of Al. Although Ag can be used as a pure metal for brazing in some applications, "Ag base" brazing alloys are more common but even as Goahead has noted, the lowest melting temperature of Ag base brazing alloys is still in the range of meltin Al.