Alumiweld

[darryl]

This maybe is just one name for it, I don't know. But it's something you can buy in stick form and weld aluminum with. More like solder I suppose- which makes me wonder- can you make an assemblage of aluminum parts and lay this stuff along the seams- then put the whole thing in the oven and have it wick into the joins?

I know you can do that with solder and copper or brass- and it works with silver solder and stainless. I don't know if Alumiweld has good enough wetting and flowing capabilities- or whether there's a certain flux that would help it. I've welded with it, and the parts I've made for my bicycle are still standing up. That would have been 6061. That was years ago and I don't remember how well it flowed. It was done without flux, and with a propane torch, and it worked as advertised.

I make a certain heat sink module for led lighting, and currently I'm assembling them with JB weld. It works- some of the modules have become damaged and the outer fins bent, and some have had the fins broken off. Some have gotten very hot by accident (too much juice through the led module for too long) and the module stayed together. I'm just wondering if I can enhance the heat conduction into the fins, and give the module more integrity by using the oven process.

I would build a jig of course to hold the parts in alignment. So far the seams will all be horizontal, and I think I can draw magic marker lines on the base part to contain the Alumiweld to the seams so it doesn't flow all over the place. I would probably do 4 or 6 of these at a time in the oven.

Which of course brings up another question- could I do this job with a dip tank? I realize that now I'd have to fasten the parts mechanically so I could dip it as a unit- and it would take quite a lot of 'weld' to fill the tank. And I don't know how well it would withstand repeated heating and cooling without becoming contaminated. This would probably take a lot more 'weld' as well, and I know this stuff isn't cheap. And if I have to pre-fasten the parts, it would take more time.

[I make chips]

I sold production equipment for aluminum brazing. Primarily automotive, the pipes onto air conditioning condensers and various fittings. It's quite a learning curve for the uninitiated as the alloy can melt as low as 100 degrees below the parent metal. Disaster is easily attained!

The best advice is to contact a local vendor of brazing alloys and discuss your application. One key of the equation is the flux. One that works well is Nocalok. But it stains the metal deeply. Just open the hood and look at the braze joints on the pipes and tubes under a car's air cond system.

Here's one of the many consumer grade products. https://www.youtube.com/channel/UC8M...0BPVn_g1dR-EkQ

[old mart]

I had some sticks of Lumiweld back in the 60's, and think that the joint had to be abraded during the process with a small stainless steel wire brush to dislodge the film of aluminium oxide. With practice, the welds could be quite good. This particular product did not use any flux.

[Rich Carlstedt]

Yes, Old Mart covered it. Oven brazing does not work. Continuous abrading of the surface is required.
In simple terms from using it in the past, you get the parts hot enough ( ~ 700 F?) and the Alumiweld melts and covers the joint and you abrade the surface of the part through the molten Alumiweld and that dislodges the Aluminum Oxide and the Alumiweld immediates alloys with the parts and "welds" the joint.
Don't expect immediate success in learning the technique..you have to try or experiment first and when you get your technique down of working your torch and rubbing with the stick , it works like a charm. ( I use MAPP Gas)
Using the SS Brush ( VERY Important !) first, breaks the old hardened Aluminum Oxide Layer and it is easier to fail/dissolves when under the molten material.
DO NOT use steel brushes !, they must be SS !
Using Steel brushes leaves Iron particles and Iron oxide is created, and that inhibits the melt.
Rich

[darryl]

Well, it did kind of seem too good to be true.