Corrosion in Stainless Steel Brazingjoint After Salt Spray Test

One of the possibilities is electrolytic corrosion, caused by the two dissimilar metals being in electrical contact both with each other and also via an electrolyte, being the salt spray.

I'm confused, you say it is a cross section but I think I see both metals but no edge. We found that even SS is attacked by acids if there are nooks and crannies for it to accumulate, welds had to be ground and polished to the same surface as the original metal.

Did you passivate after brazing?

Very relavent and important question. The process of passivation on SS reestablishes the oxide layer that gives SS its anti corrision capabilities. This is very commonly done in the food industry and is crucial to SS performing as expected.

If this is a cross section AND the void is internal with no link tot he surface, then it's unlikely to be from the accelerated salt spray test since teh salt and other potential reactions would first appear at the surface.

I suspect that the void may have been present at the time the joint/connection was made either from the preparation of the SS component or flux gasses from the brazing process.

I suppose the question i'm asking is more along the lines that "Do you know the void was not present before the test?"

When you brazed the stainless to the copper you used a flux or reducing atmosphere to get proper wetting. This surface activation stripped the chrome oxide from the surface of the stainless and left it vulnerable to corrosion. The stainless should be re-passivated after brazing.

Just after clarification from the OP.

I have presumed that the picture shown is a cross section cut AFTER the exposure time was completed. (Meaning that the section surface that we are seeing has not been exposed to the salt spray.)

That is why I'm questioning the quality of the joint and preparation. I agree that if the observation had been related to the exposed surface, then the galvanic processes are the cause, but the OP described a sub surface void. If this had been galvanic, then the void would have been filled with compressed degraded materials.

If there is no track from the surface to the void, then it was there before the test commenced.

As noted by others, we are missing some information to be of much help in this matter. A more global view of the parts would help as well as a better description of the history of the part. Your BAg-24 braze contains 28% Zinc which has a fairly low vapor pressure (vapor is also toxic). We could be looking at a void associated with local overheating and vaporizing of zinc. This may not even be a corrosion issue.

I'm with "Just an Engineer" and "welderman".

I've been sitting on the sideline struggling with reconciling the photo with the OPs description of the holes being in the SS (and not commenting). However, it looks like holes in the weld metal to me. If so ,could that be dezincification?

A weld drawing or sketch would help as would labels for all the features of the photo.

Hello All，Sorry to not descript the question clearly. The holes were found in the base metal instead of Brazing filler metal. The following is a sketch for the joint cross section. Thanks!

Still can't make out the dimensions, but it appears that the joint clearance is rather large. Your braze alloy is very fluid above the melting temperature. Recommended joint clearance is about .002" (.05mm). Suggest you apply braze metal as a paste or washer preform. Also, use a low temperature brazing flux. Clean flux residue off after braze.