grade of aluminium used for proflex XP-8 swingarm

[02GF74]

as title, anyone know what grade of aluminium uwas sed to make the swing arm?

It is bits of square box section TIG welded together, if that makes any difference.

(yep -I've contacted K2 bikes but not sure if they will reply)

Or generally, what grades of aluminuim are used to construct frames, as that may narrow it down.

What I really want to find out is what sort of heat treatment, if any, would be needed if the swing arm has a bit TIG welded on to it.


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a bit of googling tells me the it is most likely to be 6061 (needs heat treament and ageing) or 7005 (no heat treatment)

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so question now becomes what would the effect be on 6061 alloy if it has a bit TIG welded to it but not heat treated?

 

[Tim Bennet.]

I don't think bike frames are heat treated after welding, so although the aluminium tubing used might be 6061-T6, the area close to the weld will only be as strong as T0 aluminium. This will mean it's UTS drops from (IIRC) 30000 to about 18000 psi. This is why butting the tubing, increasing the area of the weld and gussetting are all used to compensate.

6061 is very weld-able (TIG or MIG), but the welded joint must be designed to compensate for the changes that occur when welded. You can't just weld up a crack in a unwelded fabrication that was relying for it's strength on being T6.

 

[Tim Bennet.]

so question now becomes what would the effect be on 6061 alloy if it has a bit TIG welded to it but not heat treated?

So specifically - if it was 6062-T6 it will almost halve in strength, if it was originally 6061-T0 then it will only loose a little.

 

[02GF74]

ok thanks - that makes a lot of sense.

Not planning to fix a thin tube but to slap on an adapter for a brake caliper. the drop out is 6 mm thick on the outer edge.

a picture will explain it better (aluminium plate is a mock up)

 

[RecordAceFromNew]

Apologies if you knew what I am bringing up here already:

As a fellow Proflex owner I can recommend the idriders.com forum and its rather extensive library. Many folks there are immensely knowledgeable.


I think XP-8s are quite rare and I have never come across one, but according to this it is essentially a rebranded 856?

For what it is worth according to the 1996 catalogue below 856 frames were 7005 series aluminium.

On the other hand e.g. a bolt on disc adaptor shown in the library there is attached below, which might help bypassing welding issues altogether.

 

[02GF74]

^^^ thanks for that info - I was just reading e-mail from K2 bikes and then mentioned the iriders forum ... so I guess I knew of it before reading your mail.

off to have a peak there.

7005 is good as from what I can tell, needs no post heat treatment.

the alternative as you correctly state is a bolt on adapter - on another forum - retrobikes - I received photos of quite a few variants, most of whcih make use of the wheel spindle not ideal - or else the second attachment point being the seat stay/swing arm joint, the first one using the small hole in the drop out. None of these are as elegant and a welded on adapter but obvioulsly are easir to do at home since I daren't attempt TIGing my frame.

FYI it is this baby, Z1 bomber that has non standard bosses for calipers - an adapter will sort that out. Originally I had it with Girvin (?) double cron forks - is that the correct term? - there stanchions extended to the top of the headset - but I change them since it reduce steering lock, an issue for me since I am a cross coutnry ricer, not downhiller.