brazing aluminum

[Alan H]

I have a couple of small projects on the boat that could be done in stainless, but could also be done in aluminum. I've read about "brazing" aluminum with a propane torch and pre-fluxed rods like those from Alumaweld and MuggyWeld. There are some video's on YouTube which make it look relatively idiot-proof.

So my question is, would this technique be appropriate for a rudderhead / tiller bracket on a 26 foot keelboat? I'd use heavy aluminum, say 3/16ths, and practice on scrap, first to figure it out. Here's one of the many video's on YT about this process.

BTW, I'd never, ever use this on rigging, wouldn't even think about it. I might, however, use it to make a windvane, somewhere down the line.

[PeterSibley]

Re: brazing aluminum

I'd want to run a few tests first. How strong is the filler rod .... thus the joint?
But for something non critical it could be good.

[MN Dave]

Re: brazing aluminum

OP: The fillets tend to be large and the strength is not bad. Due to the high heat input, the base metal will be annealed, so even if the filler metal was stronger, the HAZ will be soft. It does work for the repair of pot metal parts that can't be welded without cracking. I think that it has its place for repairing pot metal and non-critical applications. While you can braze thin aluminum with a propane torch, it takes more heat to use it on thicker parts. Mapp will work better.

It appears to be Al 802 filler metal, 98% Zn, 2% Al.
The most objective information I found is this:

http://www.silfos.com/products/catalog/Al-802-Flux-Cored-Solder-p-111.html

http://www.silfos.com/assets/product_support/technical_data_documents/Handy-One-AL-802.pdf

Somewhat higher temp: http://www.silfos.com/assets/product...One-AL-822.pdf

There is a lot more opinion than objective experience about the material. Some helpful, some uninformed opinion.

https://weldtalk.hobartwelders.com/forum/application-talk/aluminum/29715-welding-aluminum-with-propane

http://www.millerwelds.com/resources/communities/mboard/forum/welding-discussions/21143-alumiweld-rod-for-wleding-aluminum

Best information on one forum: "Give all your enemys either a sawmill or a thrashing machine...... They'd either go crazy or spend all their time trying to fix them & wouldn't have time to bother you anymore". Not helpful, but better than the rest of the uninformed speculation.

[Alan H]

Re: brazing aluminum

No problem using MAPP. I've swetted copper pipe joints that way.

[jpatrick]

Re: brazing aluminum

That much aluminum is a huge heat sink. A propane torch won't be able to get it to brazing temperatures.

Jeff

[Canoeyawl]

Re: brazing aluminum

I have welded quite a bit of aluminum with an oxy-acetylene torch over the years. Car stuff, truck tank stuff, and motorcycle stuff.

Dr. Google can fill you in on details, and it worth the search, but 30- 40 years ago that was all I had. Like any other welding it is a skill.

More here; http://www.tinmantech.com/html/alumi...ng_article.php

https://www.tinmantech.com/html/bklt_aluminum_welding.php

[Alan H]

Re: brazing aluminum

I'm good with buying a MAPP cylinder, even another torch. I don't think I want to invest in an OA setup, though. Besides, I'd have to convince the Mrs. that it would be a great idea to have acetylene tanks in the garage. Not happening.

[jpatrick]

Re: brazing aluminum

I think you would be far better off if you took the prepped parts to a welder and had them do it. The choice of mig or tig is up to the welder, of course. This is a 15 minute job. The cost won't be extreme and, more important, the parts will stay joined.

Jeff

[JimConlin]

Re: brazing aluminum

Do I read correctly that 802 aluminum is 98% zinc?
Doesn't sound like anything I'd view as structural in a marine environment.

[MN Dave]

Re: brazing aluminum

Do I read correctly that 802 aluminum is 98% zinc?
Doesn't sound like anything I'd view as structural in a marine environment.

Yes, you read it correctly. AL 802 is zinc with 2% Al. Apparently the name refers to the purpose (soldering Al) not the composition. The datasheet from Lucas Milhaupt that I linked before says that the shear strength is 18000 psi. I have to agree on both points though, I wouldn't trust zinc long term in seawater.

[upchurchmr]

Re: brazing aluminum

I recently had a cast mast base welded.
$120/ hour.
Best if you completely cut, grind, fit the pieces, and clean the weld area by sanding. Be sure to grind a relief along the weld joint also. Talk to the welder about what he wants.
Otherwise the welder does those things at his hourly cost.

I was a little shocked at the cost of my little job. Then it didn't work. The welding changed the basic shape, cause the welder was trying to get "good" penetration while clamped.

[MN Dave]

Re: brazing aluminum

Warping the part might be caused by failing to skip around and let things cool. Penetration has more to do with setup and current. Sounds like an excuse that he hoped you wouldn't understand.

One of many problems with welded aluminum is the low strength in the heat affected zone. It is strongly affected by the welding filler metal, type of weld, geometry, heat input and operator skill. An experienced welder with good equipment can minimize the heat input and that will make for a somewhat stronger weld. look for certified welders if you can, otherwise, look at their work. Big gnarly lumpy welds are a red flag. As usual, it is easy to give this bit of advice, but not so easy to give you the detail you really need. One interesting recommendation I got was to take something to a prop shop because anyone who could do good work sculpting the hodge-podge of mangled of mangled aluminum that they deal with had to be pretty good.

As for the OP's proposed rudder head, if the stresses are reasonably low, the part is accessible and easy to inspect, and the consequence of failure is inconvenient but not catastrophic, it sounds like an opportunity to learn something.

[CundysHarbor]

Re: brazing aluminum

The loading of a rudderhead on a 26 foot keel boat may be very high. I think this is no place for aluminum brazing. Best to keep looking for a nice bronze rudderhead fitting on EBAY or buy a new one. Rudderhead is a piece of critical gear. I'm thinking of a 100 lb load on a four foot tiller (when everything has gone wrong). In a two inch diameter rudderhead that translates to 4800 lb.

[Jim Ledger]

Re: brazing aluminum

I think you would be far better off if you took the prepped parts to a welder and had them do it. The choice of mig or tig is up to the welder, of course. This is a 15 minute job. The cost won't be extreme and, more important, the parts will stay joined.

Jeff

^ This

[Andrew2]

Re: brazing aluminum

Since you talk of either ally or SS, I would go for SS and stick weld it. Very easy, very strong and no corrosion probs. A few practice weld to get your hand in. Ally brazing is not that easy and def less so with a propane torch. Oxy-propane possibly, but I havn't tried it on ally, but use it often for brazing steel, or silver solder.

To add, I do use Mig on ally, but that is a whole different discussion. Not really DIY. That long but deleated thread on the fire boat, I noticed that the work was almost entirely Mig, but with nice equipement.