[Jamesinlouisiana]

Having trouble, looking for sound advice from experienced people. I have heard lots of different opions but I am only wanting facts from actual people who have experience with this. I've been making some aluminum bronze suction manifolds for salt water pumps. Due to a cost issue I've been requested to put stainless steel flanges on the aluminum bronze manifold. The materials used are as follows
Aluminum bronze manifold C95400 with a make up of
83% copper, 10% AL, 3-5% iron, .05%Mn,
1.5% Ni.
Stainless steel 316 flange
Filler rod is Aluminum bronze ERCuA1-A2
I usually weld my aluminum bronze A/C. I have tried it both ways to The stainless..A.c. And Dc
The problem- the aluminum bronze to stainless flanges weld out very well. They appear to be great to the naked eye and the weld flows very well during the process. When I go to pressure check the manifold I find leaks at the toe of the weld on the stainless side of the weld every time. They spread out in different areas of the flange. Had flanges checked and no cracking seems to be occuring and have inspected thouroughly and can find nothing visibly wrong with the weld. I believe it is in the weld mix itself or in the process. Pre-heat is done and everything is very clean. I've heard lots about this process but haven't found anyone that has actually done it for a pressure flange. Manifold will be relatvely low pressure 150psi max. Any information from someone who has made it work would be appreciated. Don't really want to hear about how you fixed grandpa's whiskey still with a brazing rod. Thanks

[Otto Nobedder]

I suspect what's happening is the heat is accelerating the re-oxidation of the chromium in the SS, making a weak bond with porous paths.

My two suggestions are to dress both surfaces with 180 grit in a DA to give it some "tooth", blow the dust off, and immediately paint it with a thin coat of flux for silver-brazing, as it will operate in the right heat range for your application and block this oxidation.

Expect other advice to follow; There's more than one way to skin this cat.

Steve S

[Poland308]

What about laying down a bead of 309 on the SS before you run the other rod?

[Jamesinlouisiana]

Thanks for the info Steve that sounds like what I may be experiencing.

[Coldman]

I've heard from lots people tell me how they have successfully joined copper alloys to stainless steel so I've taken to asking them to take me to these jobs and show me. No takers yet. I've done this because I've tried by the book without success and therefore discarded what people tell me and what I was taught in school and investigated my own methods.
The only way I have complete confidence in joining copper and its alloys to stainless steel 304, 316 and 321 for pressure purposes is silver soldering capillary joints using oxy/acet and filler Castolin Eutectic 1020XFC which is a coated high silver content filler I think over 55%. These rods are very expensive here in oz but a little goes along way. The trick is to get enough heat into the joint to make it run. I've used it for working pressures of 2800kPa in the presence of refrigerants, sulphic acids, and marine work on board long liners and bulk cement freighters. It works.

[Otto Nobedder]

I've heard from lots people tell me how they have successfully joined copper alloys to stainless steel so I've taken to asking them to take me to these jobs and show me. No takers yet. I've done this because I've tried by the book without success and therefore discarded what people tell me and what I was taught in school and investigated my own methods.
The only way I have complete confidence in joining copper and its alloys to stainless steel 304, 316 and 321 for pressure purposes is silver soldering capillary joints using oxy/acet and filler Castolin Eutectic 1020XFC which is a coated high silver content filler I think over 55%. These rods are very expensive here in oz but a little goes along way. The trick is to get enough heat into the joint to make it run. I've used it for working pressures of 2800kPa in the presence of refrigerants, sulphic acids, and marine work on board long liners and bulk cement freighters. It works.

I've melted apart many TIG-brazed joints of red brass and bronze to 304SS. I find the penetration very poor... It's more a surface fill of alloy bonded to each in a fillet than penetration of the joint. The fix I use is as you suggested. The parts are dressed as for simple sweat joints, as clean as possible, then fluxed with paste for silver-braze, and then brought to brown-hot to dull red-hot and brazed with a high-silver alloy (no flux) done in the same manner as sweating copper plumbing.

Steve S

[Braehill]

Same here.

Len

[zank]

Same here also.

This is the silver I use. Excellent quality. And their fluxes are better than any I've used.

http://cycledesignusa.com/wp/?page_id=55