View Full Version : aluminum brazing
02-02-2004, 01:27 AM
Anybody familiar with this product line? Sounds good, but with proper marketing, anything looks good.
02-02-2004, 02:15 AM
So, after giving up at the County Fair, this guy moved to the internet to sell aluminum brazing rod, how clever.
The bible of brazing info is at
click on search and type in aluminum, and you'll have plenty of good information to read.
The process was in use by Frigidare in the 1940s to make evaporators for home refridgerators, so it ain't new science.
02-04-2004, 12:01 PM
I used this stuff 20-25 years ago and it works, but it is slow and somewhat tricky. It has been sold under many trade names. Lumaweld is one I still remember. You can still find this rod today. In fact, I saw it a few days ago at Tractor Supply. It melts around 730F. You can use it to braze most aluminum alloys. For thin stuff, propane-air works. Mapp-air is good for thicker sections. The rod has a high zinc content, so don't expect a lot of strength or ductility.
You'll have to get the work clean as a Hound's tooth. Suggest aluminum oxide sandpaper. I also found that using a length of 1/16" dia CRES (302, etc) rod to occasionally stir the puddle and break the oxides as they formed helped a lot. As an experiment, some years ago I brazed together samples of non-weldable Al alloys (2024, 7075) and the samples haven't cracked yet, although in a nasty environment, I doubt the joints would have much in the way of corrosion resistance.
Having said all this, I don't think anyone with access to Tig w/AC hi-freq would ever want to join weldable aluminum alloys this way. So does this stuff have another application?
Yes. It's a pretty good way to repair die cast pot metal, like mount lugs on old carburetors, broken body trim castings on antique cars prior to re-chroming, etc. The trick with heat-short castings like this is to get some hydraulic cement (try Lowes or Home Depot). The stuff is used to plug leaky basement walls, pool walls, etc. Mix it up like plaster of paris and use it to fixture or support the casting when welding. These casting are also high zinc content with a melt point similar to the rod, so you really have a weld repair, rather than a braze.
Of course, there always the evil chemists in the group who'll suggest JB Weld!
02-04-2004, 12:22 PM
OP, You left out Devcon. I've put a few things together with both Devcon and JB Weld, and both have been real time savers compared to welding or brazing on some applications.
02-04-2004, 12:41 PM
I had to do an emergency repair on a Sewer line a while ago. I got some "Underwater Devcon" from Grainger the box said good for repairs under water.
But I guess they must have standard directions, because the directions said the part must be clean and dry.:dizzy:
Well anyway the repair worked until we could bypass the system.
02-04-2004, 12:48 PM
Mayhaps Devcon is packaging their product in a non English speaking situation now.
YOU actually read the instructions? Did you read them before or after using the Devcon? Most package insert instructions these days have print so small you need a magnifying glass to read them.
02-04-2004, 12:54 PM
After, while we were sitting around waiting for the stuff to kick:laugh:
02-04-2004, 12:55 PM
I bought some of those rods a few weeks ago at TSC and attempted to fix a crack in an ATV crankcase around the drain plug. I'm not sure if the crankcase was really aluminum or user error or if the rods just suck but it didn't work.
I started to attempt to TIG it up but am concerned the crankcase is magnesium or some other stuff ...
02-04-2004, 01:14 PM
I'd attempt to tig it. If you have a big washtub boil it with some Trisodium phosphate To degrease it. Oil has a habit of soaking into the pores in aluminum.
That might be why the rods wouldn't work.
02-04-2004, 01:15 PM
Jim, it's good to know you followed the correct procedure.
Did you wait till somebody asked "how long till this crap cures"?
02-04-2004, 04:06 PM
Morpheus, you could take a few scrapings or shavings off that crankcase and try to burn them. That'll tell you real quick whether it's aluminum or magnesium. If it's aluminum, which I suspect, it's most likely 356. Chemically clean it like Fla Jim suggests, V-groove the crack and TIG it with 4043 rod. If it's magnesium (and I don't think so), it probably would be AZ63A, AZ92A, AZ91C or AM100. If so, TIG it with AZ92A rod. If it catches fire, not to worry! - just keep the argon flowing!
Cutting magnesium plate can be interesting - much akin to being in a fireworks factory that just caught fire. But that's a story for another time.
Magnesium has kinda fallen out of favor for applications like small crankcases due to the tendancy to develop fatigue cracks from corrosion pits. Magnesium has relatively poor corrosion characteristics - it keeps trying to revert back to its natural state - which is seawater! I remember working on a DC-9 once that was ditched offshore in about 10 feet of water. Some of the rudder control mechanism was mounted to a sand cast magnesium birdcage. It disappeared in a few days, totally dissolved.
People used to talk about having 'mag wheels' on their car. Well, not hardly, especially up north Franz's way. With all the salt on the roads, they'd be drivin' on the hubs in short order!
02-04-2004, 04:22 PM
Jack here's a good reference for aluminum.
Are you planing on using the Tig you made?
Does the Freq box have a Balence dial?
02-04-2004, 04:23 PM
well, I was trying to avoid disassembling the engine which was why I tried the aluminum rods in the first place. We heated on the case for a bit on/off trying not to get the engine internals too hot. We finally got the oil cooked out of the crack pretty good but the aluminum rods just didn't really want to stick.
I have a friend that has a used lower crankcase piece that he'll give me .. but then I'm in the same boat of disassembling it all.
02-04-2004, 04:28 PM
Unless you want to degrease the snott out of it, and try 'Aluminum Devcon" (real expensive). Your going to have to dissasemble the motor:cry:
02-04-2004, 08:45 PM
Lazy man's way to degrease aluminum~
bury it in cat litter (new) and bake in oven above 350 for 6 hours.
Do NOT let wife catch you using her oven for this, cause wife + cast iron skillet will make seeing thru a welding helmet a chalenge.
02-05-2004, 01:21 AM
I just did a similar repair for a neighbor. The drain plug hole in his CT70 cracked through the threads and into the bottom of the case. We removed the engine, so I could turn it upside down. I stop drilled the crack before "V" notching it. Also I roughened the area around the repair, the cleaned it with lots of brake cleaner. If you have'nt guessed yet, I used JB Quick Weld to fill the crack and roughened area. I repaired the threads with a thread insert not a Helicoil. The kids have been riding the wheels off of it, with no leaks or problems.
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