Brazing Aluminum Question

[Nipper]

I have been reading and watching Youtube videos on brazing aluminum. Most articles state that brazed aluminum joints should be as strong as the metal itself but I'm sure not seeing that.

I bought a Air / Acetylene TurboTorch and some BernzOMatic AL3 aluminum brazing rod. I clean the metal with a Roloc pad, the torch heats up the metal fine and the brazing rod melts nice and smooth but after the joined pieces cool down I really dont have any trouble pulling it apart. once its apart I can see there was really no penetration to speak of.

I am not using any type of flux, no one in the videos I watched mentioned or used it. It this the problem? What am I missing?

[Hobart Expert]

Flux is required to braze aluminum, you'll want to get something that is designed for brazing aluminum. I would also recommend not using roloc discs to prep aluminum, they can embed hydrocarbons in the aluminum and cause issues when welding/brazing. Best bet is a stainless wire brush or carbide burr. I would also recommend cleaning the surface with Acetone/Zero Tri prior to welding/brazing.

[Nipper]

Flux is required to braze aluminum, you'll want to get something that is designed for brazing aluminum. I would also recommend not using roloc discs to prep aluminum, they can embed hydrocarbons in the aluminum and cause issues when welding/brazing. Best bet is a stainless wire brush or carbide burr. I would also recommend cleaning the surface with Acetone/Zero Tri prior to welding/brazing.

Thank you, can you recommend a brand or type of flux?

[Hobart Expert]

I can't recommend a brand but really all the fluxes designed for aluminum/magnesium brazing are very similar. The biggest thing is making sure its designed for AL and if its classified as corrosive or non-corrosive (you'll want to wash your part with water post brazing if you use a corrosive flux)

[Nipper]

Hobart 770206 Brazing Rod claims to be self fluxing. Will that work or do you still recommend using flux?

[MAC702]

There will be no penetration in brazing. Granted, all my experience is brass and copper, but I do a lot of that. What is your joint design?

EDIT: Or are you referring to the filler penetrating INTO the joint by capillary action? But same question: what is your joint design?

EDIT: Bernzomatic addressed this question on their website with this reply: "When soldering aluminum to aluminum, flux is not necessary. It can help, but it is not required for a good seal. If you wanted to go this route- I would recommend our PF200 Petroleum based plumbing flux."

https://www.bernzomatic.com/Products/Brazing-Welding-Rods/AL3

[Nipper]

Mac702,

Joint design is simple, I just wanted to try it with aluminum so these are scrap pieces. I have a piece of flat stock and I tried to braze a piece of angle to it.

You can see from the pictures below there was no capillary action. The rod melted easily and the molten rod flowed smooth but just along the edges, it looked good but I can pull it apart pretty easily.

Am I expecting too much? I keep reading "This joint should be as strong as the metal". Its not even close.

Perhaps someone can see something from these pictures.

I see now it says flux is not necessary on their website but it says nothing about it on the package. They recommend PF2000 plumbing flux if I want to use some. Everyone else says you dont need it or you can only use flux made for aluminum. ???

Here is my piece and the second picture is what it looks like when I pull it off....

[MAC702]

I'm thinking it's a heat issue. You are getting the edge of the joint hot enough to melt the filler, but the interior of the joint is cold and freezing the filler before it can flow any deeper.

Try a much smaller joint.

[Nipper]

I'm thinking it's a heat issue. You are getting the edge of the joint hot enough to melt the filler, but the interior of the joint is cold and freezing the filler before it can flow any deeper.

Try a much smaller joint.

Thanks for your time Mac702. The joint is actually pretty small. about an inch. I heated it too much a few times and the aluminum started bubbling.
The flame covers the entire spot the small piece of angle sits.

I am expecting some sort of capillary action but I had a small clamp on it, maybe it was too tight for the filler to get in?. Am I correct in thinking that?
I have tried this abut 8 times now and its the same each time.

[MAC702]

Thanks for your time Mac702. The joint is actually pretty small. about an inch. I heated it too much a few times and the aluminum started bubbling.
The flame covers the entire spot the small piece of angle sits.

I am expecting some sort of capillary action but I had a small clamp on it, maybe it was too tight for the filler to get in?. Am I correct in thinking that?

I'm still thinking you should try a smaller joint, and on smaller pieces to have less heat sink wicking away all the heat you are trying to put into the joint. Make your first practice pieces as easy as possible and go from there.

I would not expect the joint to be too tight, but as I said, I have no experience with aluminum. I do a little normal solder with copper, but a lot of brazing (silver solder) with copper and brass.

[Nipper]

I cut the pieces in half. Melted the aluminum the first time. Tried it again and it pulls right off.
I'll try again with some different aluminum.

These people on YouTube make it look so simple.

[Hobart Expert]

Hobart 770206 Brazing Rod claims to be self fluxing. Will that work or do you still recommend using flux?

Hobart 770206 does not need additional flux since its flux coated. If you're using the AL3 rods you will need flux to get any solid joint - the brazing rod is not going to flow into the joint without it.

[Nipper]

Hobart 770206 does not need additional flux since its flux coated. If you're using the AL3 rods you will need flux to get any solid joint - the brazing rod is not going to flow into the joint without it.

I really appreciate the help here!

I think both you and MAC702 are correct.

MAC702 is correct in saying Bernzomatic says you don't need flux with their AL3 rods but I sure dont see any flux on them and they are NOT working. Then they recommended using plumbing flux. I'm pretty sure that's incorrect.

"Thanks for reaching out to Bernzomatic. I apologize that Lowe's was not able to answer this for you. When soldering aluminum to aluminum flux is not necessary. It can help, but it is not required for a good seal. If you wanted to go this route- I would recommend our PF200 Petroleum based plumbing flux."

I got some Blue Demon rods locally that say they are flux coated on the package so I will give those a try and see what happens!!

[Nipper]

Just tried that. Much stronger but no way is it "as strong as the metal". At least the angle bent before it came off this time. I'm finding it hard to believe some high end bicycles are brazed together. Hmmmm.

[Dale M.]

Seriously doubt high end bicycles are "brazed".... TIG is usually process of choice for aluminum....