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PostPosted: Fri Sep 09, 2016 6:53 am 
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After our excursion in 30+ winds, & breaking an attachment stud, I also found a crack/break in one of the small support tubes.
The wings are "Magnum", off an '84 H18. They do not have the extra bracing strut.
Can anyone tell me definitively what alloy was used in these?


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PostPosted: Fri Sep 09, 2016 8:40 am 
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I can't say for certain, but I believe it to be tempered 6061 aluminum - either T4 or T6.


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PostPosted: Fri Sep 09, 2016 3:19 pm 
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SabresfortheCup wrote:
I can't say for certain, but I believe it to be tempered 6061 aluminum - either T4 or T6.

T6


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PostPosted: Mon Sep 12, 2016 6:06 pm 
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Thanks.
I'm sourcing some 6061 T6 from Aircraft Spruce. When I get the break welded, I'm going to have them add the extra crossmember between the large & small tube.
Does anyone have the measurement of how far up from bottom the horizontal bar goes?
I was thinking of eyeballing it from some online photos, but I'm sure the design engineer placed it a station X for a good reason.


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PostPosted: Tue Sep 13, 2016 9:17 am 
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edchris177 wrote:
When I get the break welded . . .
Note that when welding T6 aluminum, you remove the temper from the heat-affected zone of the weld - which reduces the strength by about half (in that area).

So what is a T6 temper? T6 tempering involves two steps—solution heat treating and aging.

Solution heat treatment is done by raising the alloy temperature to about 980 degrees F and holding it there for about an hour. The purpose of this is to dissolve all the alloying elements in a solid solution in the aluminum. Then it's quenched in water. The purpose of quenching isn't really to strengthen the alloy, although it does somewhat; it is to cool it rapidly enough to prevent the alloying elements from precipitating on cooling. This is called the T4 temper.

If you take this material and heat treat it at a temperature between 325 and 400 degrees F, the alloying elements begin to form ordered arrays of atoms in the aluminum matrix. These arrays are called GP zones, and they strengthen the aluminum considerably. This heat treatment is called aging, which results in material with a T6 temper.

Three commonly used time/temperature cycles are used for aging—one hour at 400 degrees F; five hours at 350 degrees F; and eight hours at 325 degrees F. All are equally effective.


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PostPosted: Tue Sep 13, 2016 9:33 am 
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MBounds wrote:
So what is a T6 temper? T6 tempering involves two steps—solution heat treating and aging...

Interesting. I knew that tempering aluminum was largely based on heating the material in an annealing oven, but I guess I assumed it was much more complicated than that. Matt, do you know if Hobie did this with most aluminum parts, or just some of them? I know the crossbar extrusions are tempered, as are the magnum wings and the seat of the SX wings, and probably the masts too, but I'm wondering about the legs on the SX wings. I have a set with some cracked welds where the strut was welded to the leg.


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PostPosted: Tue Sep 13, 2016 11:36 am 
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Cracks in wing parts....
Other than trying to sail, the biggest problem I have is folks who want to help with the haul out at the end of a sailing session.
I keep telling them, 'the wings were designed for compression, NOT for pulling the boat out of the water'.

We all know that there is a built-in conflict between making the wings both strong and light.
Tube welding is an art unto itself, and the results (after some time) are that the small legs crack.

The answer to get a really good MIG/TIG welding person, someone who understands temper, who can effect repairs and retain the optimum strength.

_________________
1989 Hobie SX18 Sail # 1947 "In Theory..."
'Only two things are infinite, the universe, and human stupidity. But I'm not sure about the former.'


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PostPosted: Tue Sep 13, 2016 7:50 pm 
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[quote="MBounds"So what is a T6 temper? T6 tempering involves two steps—solution heat treating and aging..[/quote]

Yes, I did a bunch of research, so I could at least discuss it intelligently with the fabricating shop.
Practically, I don't think there is an economical way to re-temper/age such a large piece.
However, the aircraft home builders do repairs. By sourcing some of the certified fixes, it seems they insert a tube inside the break,(cut at 30*), and use rosette welds, and along the seams to obtain the original strength. They can also weld patches over the tube, if a smooth finish is not important.

John, Sabres, with regards to the welds cracking, that is almost a given with 6061 IF YOU TRY TO WELD AUTOGENOUSLY. You must use a filler wire, most commonly 4043. That dilutes the weld puddle & gives satisfactory results.
The other major thing is degreasing, use acetone or toluene, not alcohol.
I believe this tubing is anodized, & that is the 3rd major consideration. The anodizing MUST BE PHYSICALLY REMOVED, by sanding or grinding.
Also make sure your welder uses AC. The alternating current blast away any left over anodizing.
This site has some very good Intel

http://www.thefabricator.com/article/al ... s-for-gmaw


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PostPosted: Wed Sep 14, 2016 9:36 am 
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Here is some good info on welding 6061.

http://www.thefabricator.com/article/al ... s-aluminum

http://www.thefabricator.com/article/al ... inum-welds

http://www.thefabricator.com/article/al ... minum-gmaw


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