Off Topic: braze or solder aluminum?

Builder's Forum
1

Got a project requires expanding my skill set.

Want to build alumnum frame out of 3/16” wall 6061 angle stock, preferably with brazed joints rather than bolting it together.

Don’t want to buy a capable welder but am aware of some products (Bernz-o-matic’s AL-3 brazing rods, KT Industries aluminum brazing kit) that can be used with a propane/air torch.

(No life safety issues over this, just a new way to mount an old dust collector blower to a new cyclonic separator & HEPA filter.)

Wondering if any forum members have any experience with these or similar products, or suggestions for other approaches.

2

Since brazing is relatively inexpenive and TIG welding is very, I'd do a quick little set of test pieces using the techniques you're interested in and destructively test them.  It will quickly become apparent which methods work and which don't.  Make sure to clean the mating surfaces with something like acetone.

3

 

   Put it this way: In aerospace fabrication, we do quite a bit of welding of structures made of 6061.  The only brazing we do is vacuum oven brazing of aluminum alloys (other than 6061) for making heat exchangers.  If strength is an issue, you have a lot of experiments ahead to see if you can get what you want from brazing.  Most of the brazing of aluminum I've seen was of tubing into sockets, or of course the stacking and brazing of heat exchanger plates in vacuum ovens.

A lot of earlier aluminum bicycle tube frames were bonded tubes in sockets using butyl or epoxy adhesives, if I recall correctly.  Then they learned TIG welding and stayed with that.

4

Thanks and agree on the destructive testing suggestion. That’s what I’d planned on, as much to evaluate process variations as to gain experience with handling materials involved.

I’ve sweated a bunch of copper pipe over the years, early failures proved preparation key to success. That applies to other processes too, most anything involving boat building.

I suspect there’s aluminum tubing & fittings I could probably use w/epoxy but likely more costly. If this brazing stuff works & proves adequate for the task, I’ll be happy. If not I’ll have learned something by the doing, then have to search out local source for TIG/MIG owner willing to do the work. Or maybe inquire of my neighbor if I can borrow his....

5

   I used some of those aluminum rods with a propane torch, and was quite pleased with the job. Had never done it before..

6

Since I started this thread some three months ago I've been "educatin' m'self" on this topic whilst staying busy w/ two part-time jobs and continuing the insulate-then-drywall-the-garage project I started last Christmas... making slow progress on readying the space where my Waterlust canoe is to be assembled.

Thanks for your comments all, paricularly ggray, who's motivated me to reappraise the aluminum brazing sticks I tried - once - with mixed results.

From my readings this aluminum stuff is tricky indeed when it comes to joining two pieces, owing to its tendency to attract oxygen molecules very quickly once its surface oxidation layer is broken. While aluminum itself has a fairly low melting point (if you want to weld it) that oxide layer's vastly more resistant, upping the ante when it comes to technique.

As with many things, preparation of the pieces to be joined is 95% of the success of a job well done. WIth these brazing rods the joining surfaces must be well-brushed clean of oxide as well as free of any other contaminants. I admit this was the flaw in my first attempt. I got antsy to try this process, failed to do as good a job as I should have prepping the pieces. Subsequent testing revealed the lack of solid bond owing to poor preparation.

As for welding? Not a simple thing if the goal is professional-looking clean, uniform beads.

Seems that's best done by TIG (Tungsten Inert Gas) welding where the tungsten welding electrode is powered by AC current, providing heat to melt the surfaces of the parts to be joined while the operator manipulates aluminum welding rod filler to add material to form a proper bead, while the welding apparatus is shielding the melt pool and arc with argon gas to keep oxygen from contaminating the weld.

MIG welding (Metal Inert Gas) similarly uses shielding gas to prevent oxidation, but the filler is supplied by the electrode's wire-feed component. This may or may not require flux, usually incorporated at the wire's core. Once the weld is completed that flux needs to be removed, requiring additional time and labor.

Many welders use DC current for their arc which doesn't play as well breaking thru that oxide layer on aluminum workpieces. So preparation is even more critical when using DC. Those whose output can be set for AC come at a higher price point.

In that the least expensive TIG welding sets I've found are upwards of $500 I'm willing to try the brazing sticks again. Propane didn't seem adequate with my one attempt so I broke out the oxygen + propane kit I bought at Sears years ago to renew a clutch pedal pivot on a SAAB 900 I was driving back then. THAT was enough heat so maybe MAPP gas instead of propane alone?

We'll see....

Thanks all for your comments. Life's for learing after all, eh?

7

Well I don’t understand the full geometry, but bolts, rivets and other mechanical fasteners will let you skip a bunch of this.

8

Cornelius, you do have a point there.

I'd considered that at first, then instead chose to look into other means that would facilitate 'lap-less' connections.

Mostly out of aesthetic considerations as much as for strength and less chance for fasteners to work loose. This project entails mounting components of a dust collection system (collection drum, HEPA filter, cyclone separator, blower - heaviest of all items - at very top) for my shop.