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crystallographic 12-02-2021 02:08 PM

Aluminum brazing, Braze-welding, TIG brazing
12 Attachment(s)
Since I first started my career in metalworking I’ve had a corresponding interest in soldering, brazing, and welding. I have taken courses, read books, attended seminars, and spoken with welding engineers, welders, and fabricators. Thus far, I’ve gotten a fair idea about what has been happening with “hot joining.”
I thought I’d put a short discourse together on some narrow applications of aluminum brazing, braze-welding, and TIG brazing. Maybe sort of helpful?

(A lot of my work has been done in the restoration of autos and aircraft, with roughly 25years spent in each area.)
Some history will be mentioned, as it pertains to some developments of methods/processes.

Aluminum Brazing and "Braze-welding"

Attachment 61855
Ryan Aircraft, aluminum fuel tank. Data tag says :"mfg 1942"
Gas weld on left. Brazed joint mounting the aluminum filler neck ring, with inspection stamp. Joining done with O/H torch - typical of all US aircraft factories during WW2, by Presidential Wartime Order. (Paul Dickerson told me that he received the order from the W.H., implemented the order across the US, and never told anyone - until I asked him.)
Can also be done with TIG.

Note that the steel filler cap mount is threaded into the aluminum filler mounting flange.
Attachment 61856

Steel filler neck/cap ring threaded into a brazed-on aluminum bung. Aluminum aircraft tank. Done with O/H torch. Can be also done with TIG. Note gas weld at bottom.
Attachment 61857

This is a (threaded) steel filler cap ring brazed to an aluminum filler neck on an old aircraft fuel tank.
(Seems that at some point in WW2 tank production, the US threaded steel tank fittings were being brazed onto the aluminum rather than screwed on.)
Done with an O/H torch. May also be done with the TIG.

Attachment 61858
This is a steel filler neck-ring “joined” to an airplane aluminum fuel tank. (Piper Aircraft, standard production for many years after WW2.)
This is a brazing operation, done with an O/A torch. Can also be accomplished with the TIG, yielding same appearance and same strength.
(I was taught this odd/unusual process by an old aviation welder, who had all the welding rating pins for air frames, landing gear, engine mounts, fuel tanks. He was also lead welder on B29, welding engine mounts for the Wright R3350 Duplex Cyclones. Was also welding lead for Walter Beech. Hell of a talent.)

(I will do this pesky operation for customers' airplane parts, by request)

Note: In a long conversation I had with Paul Dickerson (Aluminum Association past president) he filled me in on a lot of "aluminum developments" in the US. Three items follow (4th one already given, above):

One was that ALCOA (Aluminum Company of America) was responsible for the aluminum gas welding and brazing methods in the US, developing the fluxes, fillers and procedures and trainings.

Two, was that aluminum brazing was finally released as a process in 1938, and mentioned in the old ALCOA Aluminum Welding training film, of 1938.

And Three, that since the temperatures of aluminum welding and brazing occur so closely together, the process became popularly known as "Braze-welding." From my own reading I have seen X-ray photos of the brazed aluminum joints, and indeed, there are sections where the braze temp got a bit higher and there was visible fusion of the two alloys.
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TIG Brazing

The Back Story on “silver braze” using TIG:

TIG brazing 55% silver onto .120” thick steel, with zero porosity and zero heat distortion on parts :

Many years ago I was a metalman at HAC (Harah’s Auto Collection, Sparks, NV) Along with the 1400+ cars in the Collection at any given time, we would also work on cars owned by entertainers, such as Smothers Brothers, Bill Cosby, Merle Haggard, Glen Campbell, Red Skelton and etc.
I was asked to “prep for ‘show chrome’ “ a set of 5 very rare wire wheels. After I got the Very Rusty 5 wheels cleaned by hot tank and minor sandblasting, they were delivered to my work area. I could see from 6 feet away that they had been in the bottom of a swamp/river/pond/lake for a long period of time. (I had been doing "chrome prep and bright nickel prep" for a couple of years by then and was pretty familiar with plating shop practices and getting brightwork ready for the big car shows, which we entered every year.) So, I tried my various methods of filling the thousands of tanked/sandblasted rust pits - good enough to get the wheels into acid copper, our first step in the whole process.

No Luck - at all.

And …. none of the other men on the crew (35 total) had any ideas, though 6 of them were very specialized at metal/mechanical resto.
I had this expensive German 55% silver as “emergency backup” for my chrome plating work and had great success with it on difficult items, but no torch I had would get it to flow down into sandblasted deep pits and still leave a smooth tight surface, and then sandable for copper plating.

Then, late one night, I had a wild thought. So, next day I took a deep breath, a scrap of clean blasted steel, and three German rods and went out to the “Welding Shop” – where this giant old Lincoln 300Amp welder dominated one whole corner. After fiddling for an hour or two, I got the silver to lay down on the scrap steel. And – it sanded off nice and tight with the 240grit. I then took the sample over to our Plating Shop and had a coat of acid copper laid on. Sanded that off with the 400. Went back and got the bright nickel on. Hit that with 600 and then went for chrome. NICE! …. And - the 3 plating shop guys gave me a 100%!!!
Back to the Weld Shop, where I laid on all the silver we had in stock. Ordered more. Laid that on. Ordered still more. Laid on pounds of silver that was $erious coin per ounce. All 5 wheels took boxes of that filler. (At the end, the welding shop looked like the ultra cobwebby Halloween haunted house, with streamers of cottony wispy-ness hanging from every rafter, shelf, and object in that entire shop .... from the flux on the rods.)
Then I sanded and sanded …. And sanded and sanded some more. Boxes of 6in rounds later … I took the first wheel into the plating shop. A week later I was called in. All the platers – and the super – were all smiles.
BUT - “Where are the other 4?” Ah, that took more days, more boxes of gritty paper circles.
All 5 wheels got done without a single “go-back.” Not one. I was blown away, walking on the desert clouds .....

+ New stlss spokes and new stlss centers, then trued up in the Wheel Shop = DONE.

Several weeks later …. 3 suits walked out into the Metal Shop/Boat and Aircraft Shop. Serious guys with briefcases. Long chat with super, over in corner. Glances over at me a few times. Then they left.
Super came over, said, “Accounting just came all the way out here from DownTown … wanted to know what the HELL was going on with all that silver we bought … Said that was a helluva serious bill.”
I said, “Remember those wheels Glen Campbell wanted in “show chrome” ???”
.... “OH…. Right.”
(Sorry – no pix of any HAC jobs)
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TIG Silver Braze on thick steel (testing)

Attachment 61859
Two-inch thick steel billet with surface marks silver-brazed in. (TIG)
Attachment 61860
Close-up of surface marks after being TIG brazed. (First pass shown, of two passes, total.)
Part was to be plated. Surface repairs needed to be acceptable for electro-plating with copper.

Filler was 55% silver, flux kept intact on the rods during TIG brazing.
Melting point 1100F.
Cadmium content in this silver braze (“Hard Solder”) is unstable at temps above 1275F, where pitting/porosity occurs.
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TIG Brazing aluminum heat exchanger, Mercedes 300 automobile

Attachment 61861
Oil cooler on old 300 Mercedes, serious leaker in the fin area.
Ordered new cooler matching old cooler dimensions.
Band saw sliced off all needed parts from old cooler.
.... And also sliced off misc unneeded parts from new cooler.
Attachment 61862

Attachment 61863
If you look closely you can see the factory furnace braze joint - on the tank to the fin section. I had to come in very close to the factory joint - but without disturbing it, at all, in any way.
Attachment 61864
All okay. And leak tested. And on the car and test-driven and checked again.
Attachment 61865
Minimum heat means the paper tags remained stuck on.
Attachment 61866
Was a lot of brazing on the little heat exchanger.
No distortion. Good looks. No leaks.
Happy customer.
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steve.murphy 12-02-2021 08:37 PM

Thanks Kent, very interesting! Where’s the like button?

Regards Steve

dwmh 12-03-2021 08:07 AM

It's great to hear some of the history behind these processes. Thanks Kent for the lesson.

sfm1951 12-04-2021 07:31 AM

Training films
Ken, do any of the training films on this still exist to this day anywhere.?

crystallographic 12-04-2021 12:10 PM

Historical aviation training films - incl. ALCOA film

Originally Posted by sfm1951 (Post 171586)
Ken, do any of the training films on this still exist to this day anywhere.?

Hi Steve,
In my travels to old A&P training schools (and also hosting A&P instructors in my workshops) these instructors showed support of preserving the original aviation training information. Therefore my company was gifted a good number of old aviation films.
Here you will find a number of these original aviation training films now on DVD, that we obtained in original 16mm and sent down to Hollywood/Burbank for restoration and then digital transfer.

ALCOA contacted us at one point and purchased a few DVD copies of their original film for their archives.
(One film that I now have but that is not up on TMTech website is the Myron Stevens film, made by IAM machinist union. I got a copy of it recently, from a long-retired machinist (friend) who has also had long interest in Tucker cars and Indy cars.)

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