TIG Welding 2024 Aluminum ("unweldable" alloy)

[jakeru]

You've heard about the "nonweldable" aluminum alloys, right? 2024 is on the short list. It is supposed to have big problems with hot cracking when welding. I've always wanted to see if I can weld a "nonweldable" alloy, and finally got around to trying it today. And you know what, I think I'd say I got a reasonably successful weld on just my first try.
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No hot cracking tendencies were noted during welding, honestly. That is judging by my naked eye, and with bend testing. I did not do any die penetrant testing. I did use a pretty exotic, 4145 alloy filler rod I selected because, like 2024, it had a high copper content. (Unlike 2024, it had silicon it in, and lacked magnesium.) Since I haven't tried welding 2024 with any other rod yet, I woulnd't say its necessary or even best to get good results. Perhaps shearing off strips of 2024 might work just as well, if not better.

I have welded dissimilar aluminum alloys together that I struggled with hot cracking before I finally "cracked" the welding formula. I had no such problems with my 2024 welding attempt.

Judging from a couple bend tests I made, there is not a lot of ductility in the weld deposit, but there is at least *some* strength there. It did take a reasonable amount of force with the vice to get it to bend, and it did bend quite a bit in the parent metals before failing in the fusion zone.
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For reference, here is what a 2024 parent metal (not welded) "bend until failure" test looks like (ductility test) This is also heat treated to T3 rating (2024-T3). The stuff is pretty strong, it flexes a good bit (being able to fully spring back) before it yields. It's seems like one of the less ductile aluminum alloys around though.
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Maybe I did something right and stumbled across the magic 2024 welding formula on my first try, by accident? Or maybe welding 2024 is really just not as "unweldable" as the textbooks say it is?

[ducksface]

Perhaps instead of unweldable, they really mean; untalented need not apply....

[geezer]

2024 is a weldable alloy of aluminium, I not sure where you got the idea it isn't weldable, the material spec sheet for weldablility is below:

Welding may be done by use of resistance welding or inert gas consumable electrode arc method. However it must be noted that, in general, welding by any means is NOT recommended for this alloy because of the degradation of corrosion resistance that occurs as a result of weld heat. A repeat heat treatment should be done if welded.

Want something tough try 7075 aluminum

[dgarnier]

what happens if you tried it will some 4043 filler?

[sportbike]

We have used blends of 2219 and other alloy fillers for some "unweldable" alloys. Typically 2 small diameter fillers are twisted together with a drill to make a new alloy combination. We have also actually cut strips of base metal to use as welding materials in some cases for soem weird alloys (when I say weird, I'm talking Aluminum Lithium space shuttle alloys...literaly).

Some "unweldable" alloys can be welded with resistance and VPPA (varible polarity plasma arc) welding.
We also weld alumium with Friction Stir Welding, up to ~ 3" plate in a single pass, using no siielding gas at all.

Som of the issues with welding alloys that are noted as "unweldable" are cracking as noted, but corrosion, stress corrosion, extreme strength degradation, and some longer term aging problems can also be a problem. In most cases, if you are using the expensive, high strength alloys, it is for a reason, and conventional welds aren't really a viable option due to teh degradation.

[jakeru]

geezer - I came across numerous references in both books and online search to "unweldable" or "nonweldable" aluminum alloys. Here are a few:
http://www.esabna.com/us/en/educatio...num-alloys.cfm
http://www.lincolnelectric.ca/knowle...comistakes.asp
http://books.google.com/books?id=GcP...page&q&f=false

Even the weldability statement you quoted would appear to not allow TIG welding of the alloy (as that would be a "nonconsumable" electrode) welding. So I don't know? I sure have read about it being "nonweldable" over and over, but have thought it must not be quite that simple.

sportbike - Indeed it sounds like Stress Corrosion cracking could be a worry on welded 2024 if the part is subject for anything but light loading or is anything resembling a "critical weld", as I'm sure you encounter all the time at your work. I am guessing that testing stress corrosion cracking susceptibility, kind of like testing number of cycles until fatigue failure, is not very simple to do.

However, I don't think all applications of potential 2024 welding would necessarily be highly loaded or critical welds. For example, I spoke to one prospective customer who preferred using 2024 aluminum for his woodworking projects (I think making bandsaw tables and fences, etc) primarily because it "machined nicely." He said the other alloy he liked using because it "machined nicely" was 7075!

That is a cool trick about twisting two filler wires together to custom blend the composition. (And maybe this will be my excuse to pick up those safety wire twisters I've always wanted )

[geezer]

Yep read that stuff years ago, 2024, however is a borderline alloy, difficult but can be done as you yourself have shown, 7075 is on the other hand is on the other end of the doable scale. BUT even that one can be tricked with things like DURAFIX which is sort of a low temp solder method.

http://durafix.com/

[everlastsupport]

Yep read that stuff years ago, 2024, however is a borderline alloy, difficult but can be done as you yourself have shown, 7075 is on the other hand is on the other end of the doable scale. BUT even that one can be tricked with things like DURAFIX which is sort of a low temp solder method.

http://durafix.com/

I have a knock-off of durafix. Have not tried the stuff yet ($52 for 1lbs). Gave a few two a friend to try as he had a project to use them on. The if used right, it is supposed to work well.

I have tried Aluminators and gave them away (was not impressed).

Also guy, these are O/A (gas) solutions, not for TIG, but they do work. I have seen a live demo, and I bet they guy had done it 100,000 times before, looked so easy.

[jakeru]

I have used the zinc-aluminum rods to braize aluminum together with oxy-acetylene before I got my TIG setup. It is actually kind of neat, you can braze some joints that you could never weld, like join the large surfaces of two pieces of plate together. I like Geezer's idea of using it to join 7xxx series aluminum together because, well that's got zinc in it too.

Their is no inherent reason that the braizing rod should cost a lot however; its not like silver solder, where the scrap/free market prices of a key ingredient (the silver) costs a lot in "scrap value". It's only composed of Zinc and Aluminum I believe, neither of which cost very much in scrap value. The manufacturing cost should be low.

And indeed, if you don't get hung up on brand names, you can shop around and find essentially the same product for much less. Here is the same basic product, (zinc-aluminum brazing rod melting at around 800F,) sold as "Welco 52" in 1/8" rod form for $10 / lb:
http://weldingsupply.securesites.com...52-60||1|510||

[sportbike]

I am guessing that testing stress corrosion cracking susceptibility, kind of like testing number of cycles until fatigue failure, is not very simple to do.

Yeah we use very small test samples and insert them into fixtures to pre-strain the material. Then coat the fixtures and ends of the sample with wax, leaving the area of the sample that we want to test exposed. The samples then go into a salt spray test machine and run for a set time. They are inspected on set intervals and recorded when they break. We also have dead load testers that we put sample sin and hang a weight on a mechanism that has a pulley system to multiply the force. The sample is held at a constant load while a corrosive (usually salt water) bath flows over the sample. There is a switch that stops a timer when the specimen breaks.

All takes a long time to setup and run, but the only way to know for sure sis to test. The issue then becomes applying the test data to a new design and coming up with acceptable failure criteria. In aluminum, not all cracks are failures, it all relates to how many and how big the cracks are.

This was a recent problem on an airbus passenger plane that had a portion of the cabin rip apart. Pretty much all aircraft are just waiting to fail (especially helicopters!)

[jakeru]

I had typed up and lost a response to this TWO times now, so pardon the brevity but hopefully third time will be a charm.

It's clear you know your metallurgy, John. Thanks for the info on SCC.

It was illuminating for me to learn that wax a coating would prevent or retard SCC, and also to learn that a constant (and not cyclical) pressure was applied with a corrosive (salt spray) environment. I wonder if any other coatings would similar prevent or retard the SCC, such as an expoxy-based paint/primer or powdercoat (impermeable to water), or perhaps a sacrificial anode type of coating, like Zinc-based, cold galvanizing spray.

[sportbike]

I had typed up and lost a response to this TWO times now, so pardon the brevity but hopefully third time will be a charm.

It's clear you know your metallurgy, John. Thanks for the info on SCC.

It was illuminating for me to learn that wax a coating would prevent or retard SCC, and also to learn that a constant (and not cyclical) pressure was applied with a corrosive (salt spray) environment. I wonder if any other coatings would similar prevent or retard the SCC, such as an expoxy-based paint/primer or powdercoat (impermeable to water), or perhaps a sacrificial anode type of coating, like Zinc-based, cold galvanizing spray.

The wax is only a corrosion inhibitor, as the saltwater does not come in contact with the small test frames (we re-use those). The area of the sample that we test is exposed to the saltwater (or other environment) bath. Plenty of other items could be used to protect the material, but all of them can have scratch or other small damage that can allow stress corrosion cracking.

Stress corrosion is not really a fatigue related problem. Many times it is referred to as fatigue related but it occurs in a steady load condition, which is why is can be very unexpected and puzzling. Some materials and tempers are more akin to SCC than others (7075-T6 is, while 7050-T7451 is not, thus the 7050 is often used in aircraft). It is not necessarily that general corrosion always results in SCC, it is that some materials exhibit SCC when they otherwise can apprear "healthy" due to micro cracks forming, only when the part is under strain. It is also not the samt as failure due to corrosion, which generally makes the part have a smaller cross section, increasing the stress.