Aluminum Tank

[PineKnot]

I'm getting ready to fab an aux fuel (diesel) tank for my pickup from .100 or .125 treadbrite aluminum. It will be a "L" shaped cross bed to go under/around my tool box. All corners will be Tig welded with my 180 SD, as I have no access to a brake that size. I'm comfortable enough with the basic welding part, but this is a larger project than normal for me. I'd appreciate any advice on tacking (should I tack the whole thing before running the joints on any of it? And what spacing?) and the best general strategy for assembly.
How long a bead should I run at one time and what's the best way to manage heat expansion for putting it together with no surprises. I assume I'll be using 4043 filler, but any suggestions on that, or for that matter anything else I should know would be much appreciated. Obviously I need to make this both look great and be structurally sound. Thanks in advance.

[MAC702]

Yes, I would definitely tack the whole assembly as you lay it out before running any real beads. At no time will you need the strength of beads during construction, so tacking is called for here.

What alloy is your treadbrite?

[PineKnot]

Haven't bought the material yet. I know the treadbrite is available in 3003, but can it be had in 6061 or a better alloy for this purpose? What do you recommend, and would the relative softness of 3003 be an issue? As you can see I'm headed into (for me) uncharted waters, and would appreciate all the advice I can get. The tank will be about 9" deep in the main part and about 20" wide and 48" long with the 4" leg of the "L" standing above that and with interior baffles. It will supprt only its own weight and the fuel, so I wouldn't think strength would be too much of an issue.

[MAC702]

4043 is designed for welding 6xxx series aluminum alloys. It may also be used to weld 3xxx series alloys or 2xxx alloys. 4043 has a lower melting point and more fluidity than the 5xxx series filler alloys, and is preferred by many welders because it "wets and flows better" and it's less sensitive to weld cracking with the 6xxx series base alloys. 4043 also makes brighter looking MIG welds with less smut because it doesn't contain magnesium. 4043 gives more weld penetration than 5356, but produces welds with less ductility than those made using 5356.

5356 filler has become a very common filler alloy because of its good strength. It is designed to weld 5xxx series structural alloys and 6xxx series extrusions, basically anything other than castings, because castings are high in silicon. Its one limitation is that 5356 is not suitable for service temperatures exceeding 150 degrees Fahrenheit. The formation of Al2Mg at elevated temperatures at the grain boundaries makes the alloys prone to stress corrosion. For components that will be anodized after welding, 5356 is recommended over 4043, which turns jet black when anodized.

Do you expect a service temperature above 150 degrees? Do you plan to have the tank anodized? Your options are still fairly open at this point, based on some of the considerations I've mentioned.

Here's a chart that tells you fillers depending on what characteristics you are looking for in the weld, based on what alloy you are TIG welding.

[PineKnot]

Thanks for your interest in my project. No anodizing and no service temps above 150 F. This is going to be a polished natural finish (the reason for treadbrite) aux fuel tank for the bed of my diesel pickup. I'd be interested in knowing if treadbrite comes in alloys other than 3003, and if one of them would be better suited for my purpose. Should 1100 filler be considered if 3003 is the choice?

[NorthernLights]

I am also planning on building an auxillary fuel tank for my truck out of 3003 brite aluminum diamond plate. I special ordered some 1100 TIG filler because it's suppose to be a better color match than 4043. I haven't tried either yet. I have some coupons cut out and hope to weld some samples this weekend with both 1100 and 4043 fillers. Hopefully I can have some pictures before Monday.

I had to order 10# (minimum special order amount) of 1100 through my local Airgas. It was about $6.50 / pound and took about 3 weeks to get in.

I also have 1100 and 4043 wires for my spoolgun I could try also. It would go faster than TIG, but may have leaks due to cold starts of MIG and may not look as good. I am planning on making a wedge shaped tank similar to TransferFlow's design.

[Paul Seaman]

Northernlights:
Check out the online places for tig rod, I think that was a bit high. I buy 4043 for $4 Lb, haven't needed any 1100 but it sounds high, considering it is a less expensive alloy to make. Also airgas sells 1100 in 1Lb tubes under the Radnor brand. I know they ship between stores, I have done it many times.

Peace,

[Sberry]

I would take it to a shop and get it broke so there would be only 2 full length welds. That would be worth every penny. One of them you could hide so it wouldnt be seen. This would keep warpage to a minimum. Considering the cost of materials I would be very tempted to at least price a commercial made unit and get on with my life.

[PineKnot]

Considering the cost of materials I would be very tempted to at least price a commercial made unit and get on with my life.

Hey, no fair! This thought had been lurking, but like any good builder I suppressed it. Told a friend today it will probably only cost 40 percent more to build it. Seriously, I've been down that road and have some significant improvements I'd like to make. Generally, the feeding, venting, and filling characteristics of these commercial tank options are horrendous. I'm talking about a true aux tank, properly plumbed in with a six port two way solenoid valve and its own sender and gauge, not a nurse tank for other equipment, and not a gravity feed into the stock tank. Yea, I know, I could buy a TransferFlow, but they don't have exactly what I want either.
Surely this forum has a lot of people experience in fabricating aluminum who haven't been heard from yet. Any suggestions?

[Justin00Stang]

Local surplus place by me is about 30% cheaper on alum 4x8 diamond plate than the local steel/metal places.

[kid]

I have built quit a few aluminum tanks out of .125" 3003 alloy, using 3/32" 4043 filler. You should be able to build it for alot cheaper than buying. Tho I have not used tread plate. I tack (with no filler) it completly together before welding complete, with the exception of the baffles. If nothing else,get your baffles bent (brake) to aid in welding in (lap weld is easier than a baffle on edge). I also suggest you clamp the baffle & tank panel to your table or you will see excessive warping when you weld in the baffle. Another thing I do is pressure test the tank to 4.5 PSI, Be very carefull not to over pressure. & again, I suggest you fab a "holding" fixture to keep the tank from expanding & it will too. Flat sides with square corners do not take pressure well. I enjoy building aluminum tanks as I am sure you will. Something about laying down some aluminum beads..

[imported_Harold]

Not sure I would use 1100 filler. I have been cautioned a few times not to use it for any structural welds unless it was the recommended filler for the material being used. I know it flows nice and looks good but...
Also probably the reason my suppliers dont stock it in any large quantity.
Harold

[PineKnot]

I have built quit a few aluminum tanks out of .125" 3003 alloy, using 3/32" 4043 filler. You should be able to build it for alot cheaper than buying. Tho I have not used tread plate. I tack (with no filler) it completly together before welding complete, with the exception of the baffles. If nothing else,get your baffles bent (brake) to aid in welding in (lap weld is easier than a baffle on edge). I also suggest you clamp the baffle & tank panel to your table or you will see excessive warping when you weld in the baffle. Another thing I do is pressure test the tank to 4.5 PSI, Be very carefull not to over pressure. & again, I suggest you fab a "holding" fixture to keep the tank from expanding & it will too. Flat sides with square corners do not take pressure well. I enjoy building aluminum tanks as I am sure you will. Something about laying down some aluminum beads..

Kid, Thanks for that. Just the sort of suggestions I'm looking for!

Harold, That makes sense, since I think 1100 is pure Al and would be dead soft. No reason not to use 4043 that I can see.