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Any good experiences welding Al armour here?

 

The rear sponson on my CVR(T) was quite badly damaged plus somebody patched it with some 6061 or something and the patch just rotted out in a most impressive manner. I wound up cutting it off entirely. Now I need to find some compatible material for a replacement as well as some filler.

 

It's about 7'1"x6"x.25" but larger would be fine (up to a point of course).

 

It's 7017 so I believe I can use any of 7017, 7018, 7020, 7039, 5059, 5083.

The documents I can find give instructions for MIG so I'd have to find some wire as well.

I was actually wondering if folks had tried TIG on this stuff? If so I could just cut some thin strips off the good material I cut off and use that as filler.

 

thanks,

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I have TIG wleded a fair amount of AL lately, not 7XXX series, 6061, but the same principles apply. First and foremost, pre-heat is a must to around 400F or you will get cold-cracking as soon as you move the weld puddle . Even with pre-heat, I was pushing well over 250 amps into it at first on 1/4" material , then backing the pedal off as the material heats up.

I used an 1/8" Zirconiated rod, 1/2" lens(cup) and pure Argon. A water cooled torch is a must, as well as a high frequency over-lapping square wave on the AC setting. If you can find a machine with adjustable HF then all the better although your into a pretty expensive welder at this point.

 

I also would not use old material as filler, filler rod for TIG is specially formulated and typically differs from the base metal a little, usually the addition of some alloying agent, 1% of this or that. This is to prevent corrosive stress cracking, an example would be 300 series stainless where they add 1% titanium, etc.

 

Your biggest problem will be getting all the surrounding metal hot enough so it doesn't suck all the heat out of your weld, especially with pieces that big. Anything you can remove from the surrounding structure will help here.

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I've got a miller Dynasty so I'm pretty set for a TIG welder.

Apparently, armour is a bit unusual in that preheat is normally contraindicated due to the particulars of the alloy and the softening effect, they recommend buttering as a solution to face cracking. I would love to get the right filler but since I can't even seem to find material for the patch... I can tell you whatever they used before didn't work out.

 

rot.JPG

 

I found a somewhat useful guide for MIG welding but still nothing useful for TIG using these alloys.

 

http://www.scorpiontank.co.uk/PDFs/Repair%20Overhaul%20etc/Aluminium%20Armour%20Welding%20Repair%20Guide%20%288%20November%202011%29.pdf

 

Aluminium Armour Welding(8 Nov2011).pdf

 

Normally for heavy Al repair Helium or He/Ar does a better job of energy transfer and one can use DC TIG with proper cleaning to dump double the heat as balanced AC but I just don't know in this case.

 

I have TIG wleded a fair amount of AL lately, not 7XXX series, 6061, but the same principles apply. First and foremost, pre-heat is a must to around 400F or you will get cold-cracking as soon as you move the weld puddle . Even with pre-heat, I was pushing well over 250 amps into it at first on 1/4" material , then backing the pedal off as the material heats up.

I used an 1/8" Zirconiated rod, 1/2" lens(cup) and pure Argon. A water cooled torch is a must, as well as a high frequency over-lapping square wave on the AC setting. If you can find a machine with adjustable HF then all the better although your into a pretty expensive welder at this point.

 

I also would not use old material as filler, filler rod for TIG is specially formulated and typically differs from the base metal a little, usually the addition of some alloying agent, 1% of this or that. This is to prevent corrosive stress cracking, an example would be 300 series stainless where they add 1% titanium, etc.

 

Your biggest problem will be getting all the surrounding metal hot enough so it doesn't suck all the heat out of your weld, especially with pieces that big. Anything you can remove from the surrounding structure will help here.

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The plot thickens, I just found this article dealing more with aluminum-lithium armor than the AL-Zn-Mn that I'm dealing with but the interesting bit is they used two different alloy filler rods twisted together to get a more chemically useful mix and that might have some applicability to my project.

 

http://www.asminternational.org/documents/10192/1898681/amp16310p027.pdf/2dc284ad-7321-4343-8877-094f643e3911

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well based on what that article implies, and what another one I read stated(as well as the Wikipedia article), the original armor was simply prone to corrosion stress cracking and they re-formulated it in 1978. Even the article you linked to states at the beginning that welding should be a last resort after all other methods have been considered. Added all up it implies that welding this stuff is a hat-trick IMHO.

 

To reduce weight, AL alloy armour - using AA7017 made to Alcan E74S specification (Al + Zn 3.9; Mn 2.6) - was originally selected instead of steel; research revealed that it provided greater protection from artillery shell-splinters because of its areal density.[3] However, this alloy suffered from stress corrosion cracking over time, especially around the gun mantlets of the Scimitar, and an improved specification armour (AA1707 made to MVEE-1318B with strict quality control) was fitted from 1978.

 

(

I've got a miller Dynasty so I'm pretty set for a TIG welder. Apparently, armour is a bit unusual in that preheat is normally contraindicated due to the particulars of the alloy and the softening effect, they recommend buttering as a solution to face cracking.

 

I found a somewhat useful guide for MIG welding but still nothing useful for TIG using these alloys.

 

I've never done MIG, so can't comment, but I believe MIG is almost always DCRP in order to melt the filler wire. Their instructions to start with base metal at room temperature and run 400 amps thru the torch + 99% pure Argon is interesting . If this is done, wouldn't the surrounding base metal quickly exceed well above 400F regardless from the high conductivity of AL? I know when I got done, my part was too hot to touch for 2+ hours, but it didn't leak under pressure and that's what I was after.

 

My old TIG only goes 320 amps regardless, A Miller Dynasty TIG that can crank out 400+ amps is the 700 model at around $12K.

 

(

Normally for heavy Al repair Helium or He/Ar does a better job of energy transfer and one can use DC TIG with proper cleaning to dump double the heat as balanced AC but I just don't know in this case.
I only tried TIG DCSP once on AL just out of Curiosity. What I remember is I could see the layer of Oxide floating on top like a crust, while the metal underneath liquefied and then dripped or sagged down. What they taught me in school was that the purpose of the AC wave was break/shatter the oxide layer and that allows you to weld the metal underneath. The only problem I have is my old machine does not have adjustable AC frequency control, the AC is rather slow and you can hear it slowly crackling whereas on the new machines it's so fast it sounds like a high pitched buzzing. The end result Is I have to use more power than I would under ideal conditions, but at least I have the square wave that keeps the arc fairly stable.

Have not tried Helium mixes either but from what I remember the HE gives you a wider and shallower weld puddle for thinner sections?

 

Anyway, I don't consider myself a professional welder by any circumstances . I just do it because I have to as part of my job. Thankfully AL is typically not on the menu and it's always a little stressful. I could have 2 or 3 days machining time to create my parts, and then in the welding booth I will either finish the job in an hour or 2 or possibly wind up with a pile of garbage that sends me back to the mills and lathes for round 2. That's more excitement than I typically crave :)

 

Let us know how you make out on the 7017, it should be an interesting experience.

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I have to agree TIG filler rods have additional metals in them. But I have heard that using thing strips of parent metal on Land Rover repairs is common as the old series ones in particular were a weird alloy.

 

Stress corrosion cracking would not be a concern as it is a service induced defect requiring stress (either inherent or applied and a corrosive environment). There are many types of stress SCC. This type of cracking grows over time and the bit you are looking at welding is not highly stressed.

 

Aluminium needs to be perfectly clean, use a proper welding cleaner, not something like brake cleaner as the residue gives of phosgene gas when heated......not good.

 

Preheat and maintaining the heat is one of the bigger issues as the thicker sections will suck the heat out and cause cracking.

 

I think welding as the last resort would be because it would damage the armour hardness, but again thats no big deal unless you need to be bullet proof. I have never delved deep into CVRT armour but often it is the outer surfaces that are hard with the centre normal. If you have an alloy composition I can dig around for a welding procedure

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Seems like the buttering of the surrounding area is a big help but it does seem a bit of a chancy proposition, I think I'll be just bolting in the new motor mount! I'm almost tempted to just bolt on a new rear sponson, it's mostly pretty hidden after all but I'll have a go at the remainder of what I cut off and a spare hatch I have sitting in the pile and see how it actually is to do in practice.

 

Based on the rot I saw where repairs were done it looks like alloy matters, of course I don't know if that was ten or fourty years ago so it might be that if you keep it painted so it can't get at the atmosphere it's a good long-term solution.

 

Finding the 701x seems to be the real sticking point so far.

 

I had a welding shop for years but I mostly ran steel or the common 6061 type aluminum. I got pretty handy welding up broken castings and such but there is a big difference between any of that and this stuff.

I ran just enough MIG Al to know I wanted a nice TIG welder. Actually it wasn't bad but I was trying to do it without a spool-gun.

Speaking of, there exists a whole class of welder (usually a spool gun but stick works too) around the idea of using car batteries. I'm thinking the CVR(T) is a great candidate with the slave start port and the big 24V system so if I could find some wire I'd be inclined to give that a try. http://readywelder.com/ they even have military kits all set up but I might fabricate my own using a very heavy ESAB wire feeder I've got lying around.

 

I don't need the full 400A for tig since I'm just sticking the thin stuff on and not welding thick plate to thick plate, I'm hoping my ~300A is plenty.

 

well based on what that article implies, and what another one I read stated(as well as the Wikipedia article), the original armor was simply prone to corrosion stress cracking and they re-formulated it in 1978. Even the article you linked to states at the beginning that welding should be a last resort after all other methods have been considered. Added all up it implies that welding this stuff is a hat-trick IMHO.

 

 

 

(

 

I've never done MIG, so can't comment, but I believe MIG is almost always DCRP in order to melt the filler wire. Their instructions to start with base metal at room temperature and run 400 amps thru the torch + 99% pure Argon is interesting . If this is done, wouldn't the surrounding base metal quickly exceed well above 400F regardless from the high conductivity of AL? I know when I got done, my part was too hot to touch for 2+ hours, but it didn't leak under pressure and that's what I was after.

 

My old TIG only goes 320 amps regardless, A Miller Dynasty TIG that can crank out 400+ amps is the 700 model at around $12K.

 

( I only tried TIG DCSP once on AL just out of Curiosity. What I remember is I could see the layer of Oxide floating on top like a crust, while the metal underneath liquefied and then dripped or sagged down. What they taught me in school was that the purpose of the AC wave was break/shatter the oxide layer and that allows you to weld the metal underneath. The only problem I have is my old machine does not have adjustable AC frequency control, the AC is rather slow and you can hear it slowly crackling whereas on the new machines it's so fast it sounds like a high pitched buzzing. The end result Is I have to use more power than I would under ideal conditions, but at least I have the square wave that keeps the arc fairly stable.

Have not tried Helium mixes either but from what I remember the HE gives you a wider and shallower weld puddle for thinner sections?

 

Anyway, I don't consider myself a professional welder by any circumstances . I just do it because I have to as part of my job. Thankfully AL is typically not on the menu and it's always a little stressful. I could have 2 or 3 days machining time to create my parts, and then in the welding booth I will either finish the job in an hour or 2 or possibly wind up with a pile of garbage that sends me back to the mills and lathes for round 2. That's more excitement than I typically crave :)

 

Let us know how you make out on the 7017, it should be an interesting experience.

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I finally caught a bit of a break regarding my needed hull repairs.

Looks like 5556 is the desired alloy for filler and it's fairly available (if not inexpensive).

I'm still looking for a source of the plate metal to attach though.

 

A member on another site found this and sent it to me, which showed me the 5556.

http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-DTL/download.php?spec=MIL-DTL-32505.052307.pdf

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Every CVR(T) owner should buy this book from Abe books or elsewhere. It was never sold by Alcan but given out at lectures.

 

As technical people you FESMNDT and TELETECH would love the info contained inside, lots of welding information.

 

The question that needs answering is, what caused the corrosion in the first place? Is it a lack of isolation between dissimilar metals?

 

Best regards

 

Robin

Alcan book 1.jpg

Alcan book 2.jpg

Alcan book 3.jpg

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Robin, no copies on ABE but I'll keep an eye out, thanks much.

 

As to the original corrosion, that's just because someone repaired a chunk of my sponson with the wrong material (6061 I expect).

Based on the damage to the hull it looks like there was either a thrown track or a bent/collapsed tensioner and that caused the sponson damage originally. Once that was done they created a battery. It might be the case that if the sponson had been kept painted it might not have been able to corrode but I don't want to take that chance.

 

Every CVR(T) owner should buy this book from Abe books or elsewhere. It was never sold by Alcan but given out at lectures.

 

As technical people you FESMNDT and TELETECH would love the info contained inside, lots of welding information.

 

The question that needs answering is, what caused the corrosion in the first place? Is it a lack of isolation between dissimilar metals?

 

Best regards

 

Robin

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Robin, no copies on ABE but I'll keep an eye out, thanks much.

 

If you look on this page you will find the book for sale on a number of sites:-

 

https://www.google.co.uk/search?sourceid=navclient&aq=&oq=military+uses+of+aluminum&ie=UTF-8&rlz=1T4GZAZ_enGB367GB367&q=military+uses+of+aluminum+alcan+booth&gs_l=hp..1.41l1016.0.0.2.387838...........0.TphHkrkb2Gs

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