Weld patch vs. rivet?

[daved20319]

Everything I've read says the shell on my AS is 6061 aluminum, a weldable alloy. I have some patching to do, so why couldn't those patches be welded instead of riveted? I realize this may be heretical , but it's been on my mind for awhile. Your thoughts in this regard will be much appreciated.

Dave

[mimiandrews]

Your year model is more probably 2024 aluminum which is not weldable.

[daved20319]

http://www.airforums.com/forums/f381...ge-141412.html This particular subject has made me more than a little crazy at times, seems to be lots of opinion and speculation with very little hard data . This post by Andy is the only thing I've seen that says AS stopped "experimenting" and switched to 6061 in 1972 and used it until 1977/78, putting my AS right in the middle. The one thing I haven't been able to get an answer on is whether it was still Alclad or not, but I've decided it really doesn't matter that much. Next ?

Dave

[GeocamperAS]

Welding or soldering aluminum is a skill above and beyond normal welding. The temperature that is needed for the alloy to bond is very close to the temperature at which it will melt (destroy) the aluminum. I would only let someone with years of experience do it.

[ArtisanAir]

Maybe try and weld it. If it doesn't work then your just stuck making a slightly bigger patch to rivet on. I've welded 3003 before. I know a fab shop that only uses 6061 for firetrucks, they weld on those all day long, but I'm sure they are using some thick gauges. Good luck are you going to tig or mig it?

[Tim A.]

Welding, other than spot welding, any sort of sheet metal can be difficult. Welding of aluminum is almost always inert-gas welding which requires suitable equipment. Riveting is much simpler, works well, and is less likely to warp the sheets of metal.

My father was a sheet-metal worker, but not an expert welder. I still remember tales of him "blowing holes" in sheet metal when he tried to weld it!

Tim

[rick670]

Originally Posted by daved20319

Everything I've read says the shell on my AS is 6061 aluminum, a weldable alloy. I have some patching to do, so why couldn't those patches be welded instead of riveted? I realize this may be heretical , but it's been on my mind for awhile. Your thoughts in this regard will be much appreciated.

Dave

I was certified Alum welder for many years. Both tig and mig. Riveting would be far superior in your case. You would need the back side open. 2 pieces butted together with a heavy steel plate on the back to draw off heat. It will probably warp. You would need a special tig setup
or you could rivet a heavy AL backing to the seam and weld it but I don't really see the advantage. You would lose the temper in the aluminum and need to grind off the weld for cosmetic reasons. Planes builders rivet and do not weld
also if you ever needed to replace that section in the future forget it. Hope this helped.

[clydecrashcu]

I am not a welder but have been around metal work being welded, etc. It is my understanding and from what previous posts have been to this thread that welding thin aluminum is an art. A friend of mine that was a welder worked with another welder that could weld Coors cans. I have not personally seen that done. Popping or blowing holes in sheet metal does happen. For my bucks I would replace the whole panel if needed or be creative in your patch. If you are still considering welding the aluminum if you can, find a expert welder that does aluminum. It is also my understanding that welding can actualy weaken/fatigue the metal. Aluminum frames have a tendencie to fatigue at the weld on cross beams etc. that comes from another friend that worked at a trailer factory that did aluminum frames on horse trailers, etc. I am guessing others will chime in and either dispute my statements or agree. I tend to go with the thoughts from a person trained and works in the field (welder,carpenter, etc.) Thats my dollars worth of wisdom so lets go get a cup of coffee and discuss this more.

[Royce]

Many years ago I bought a small tube of rod that was reported to be able to "weld" Aluminum, Zinc plated, Pot metal, and about anything with this magic rod using a propane torch. The demonstrator was welding 1/2" holes in the bottom of pop cans without any cleaning prep. I am sure it was not weld of course, but rather a solder or maybe a braze type of attachment but it was pretty impressive. I bought it to weld an aluminum post cap on a zinc plated post, that was almost 25 years ago now and it has held with constant tension on the cap. As has been stated if you could get a good heat sink behind the skin you might get by but I would not attempt to weld a patch, maybe a short split or small hole. Be ready to file the patch and paint afterward. I think it must have been this material. http://www.alumiweld.com/index.html

[MelGoddard]

Originally Posted by GeocamperAS

Welding or soldering aluminum is a skill above and beyond normal welding. The temperature that is needed for the alloy to bond is very close to the temperature at which it will melt (destroy) the aluminum. I would only let someone with years of experience do it.

Stay with rivets!
Welding requires heat treatment that is way above the average skills and equipment.
100+ years of aircraft mfg. must have proved the 'test of time.'

(Retired Cdn. Aircraft Engineer)

[SMLJeep]

As a former certified aircraft welder I agree with rick670, riveting is the way to go.

[daved20319]

Thanks to all of you for the responses, heat treat was the factor I was missing in my thinking, the rest of it I could have handled one way or another. Looks like I'll stick to riveting, that's what I bought all those fancy tools for, after all . Later.

Dave

[tjoneillMO]

Some aluminum welding information:

2024 is a common aircraft alloy that is heat treatable because it's alloyed with copper. When you do this it makes it stronger but also reduces corrosion resistance, and makes it more difficult to weld--not impossible but more difficult than normal.

Alclad alloys incorporate a layer of pure (alloy 1100) aluminum on one side as this is the most corrosion-resistant aluminum alloy. Alclad 2024 and 7075 are typically used for aircraft skins. 7075 is the strongest aluminum alloy but is not weldable as it is alloyed with zinc and also heat treated. Newer aluminum-lithium alloys are now emerging in aerospace construction--these are welded with a process called friction stir welding.

6061 is a very weldable heat treatable alloy (silicon-magnesium alloy group) but welding actually softens the material if it is in the heat treated condition (indicated by the temper designation T6, i.e., 6061-T6). 6061 is widely used and welded though. For best strength it is procured in the softest condition (6061-T0) and then welded and heat treated to the T6 condition. Heat treating aluminum is difficult and requires complex and well controlled furnaces that use inert gasses or vacuum.

Aluminum welds need to be continuous and completely penetrated through the material thickness to resist cracking when subjected to fatigue stresses (like an aircraft or trailer). Unwelded areas act to concentrate stress and become cracks. Another item is to fill the crater that almost always forms at the end of an aluminum weld due to its high thermal expansion characteristics.

The best alloy for as-welded strength is in the 5xxx (magnesium alloy) series. 5052-H321 is a very popular sheet alloy that is strain-hardened (stretched) at the mill to make it stronger. This also has the best weldability and is easily formed.

Welding aluminum requires inert gas processes--either TIG or MIG. MIG is easier than TIG. Most aluminum can be welded with either 4043 or 5356 filler metal. 4043 is more fluid and forgiving, 5356 is stronger. If welding 5052, use 5356 filler for best strength.

I am a welding engineer and have been a certified welder for about 40 years and am considering using MIG to fill rivet holes in my '76 safari which is shell off at this point. Surface finish/appearance will be an issue as well where welds are placed--I have a large tear in the lower rear that I am going to do a rivet patch or complete section replacement--still undecided on this depending on whether I can get the formed lower rear sheet. Anyone who has done this please feel free to comment.

Distortion in sheet is always an issue, one helpful technique is LIGHTLY peen the weld with a domed hammer to "stretch" the material. Think of a weld as an incredibly strong rubber band pulling in all directions on the adjacent material--as it cools it has to either stretch or crack.

There will be a test later....