Thanks, these are good background information but I was hoping that someone had experience of joining aluminium to inconel.
We have quite a lot of experience with torch/induction brazing of aluminium alloys and inconel alloys but have never brazed the two together.
We have a customer who is designing a motor-sport engine that requires an assembly to be constructed from a mixture of aluminium and inconel alloys brazed together.
Due to the differing thermal conduction and expansion properties of the two alloys we would expect difficulties achieving a servicable joint using traditional brazing techniques.
Has anyone any suggestions regarding filler alloys and heating methods?
The aluminium will probably be one of the 6000 series alloys.
You also need to make sure that the difference in TC leaves the joint in compression, not tension. I know that this sounds basic, but we have all seen it missed (not by us of course).
My hunch is that one of the two metals will need to be pre-treated since you probably will not be able to find a flux that is compatible with both.
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Rust never sleeps
Neither should your protection
In a prior life, we made braze joints between various refractory alloys (Mo, Re, W) and superalloys, that were intended to be leak-tight to high temperature gas (~1500 F). The metallurgists tried a lot of different combinations, and Ed's post is quite correct, the tough thing is avoiding thermal "shocks" due to equipment faults. One thing we always came back to is the use of near-pure gold as a braze alloy. Its high malleability helps to maintain a seal even under conditions that would rupture other metals.
I've been thinking about EdStainless’s remark about tension and he's right, of course. However you can have a successful braze joint in tension as long as the tension doesn't weaken it too much. Sometimes this is the only way to do it. Much of what we do is carbide saw tips on saw blades. When the steel shrinks it wants to bow the carbide and thus creates tension. If there is too much tension the part will snap as it cools.
However proper selection of carbide and braze alloy combined with proper braze techniques makes joints that are successful. Some may be in tension and I rather suspect that most are.
This is an example that joints in tension can be successful if that is the only way the joint can be designed. However I will definitely second EdStainless that it is not the best way to do it if there is a choice.
If you don’t have it then get The Brazing Book from Handy and Harman. It is very good on basic joint design.
