Maintenance & Technical > KX500 Aluminum Frame Conversion (AFC)
Dutch 500AF Conversion 250KXF 2009
Jos197AF:
--- Quote from: mxaniac on March 25, 2014, 07:41:16 AM ---So I know I'm sounding like a broken record here (what is the modern phrase for that?) so I'll bring this up one more time and shut up about it. You really need to take a second look at 7075 on the frame. I've had field failures with product using 7075 because of the smallest surface scratches from machining which promoted SCC. This has nothing to do with welding, machined parts in 7075 can fail under pretty benign conditions. 7075 needs to be in the T7 temper for this application but you might very well anneal the rest of the frame too much by doing so. You need to look at the aging curves of all the alloys involved and see if a compatible process exists. If you don't you could end up in the hospitol or under ground.
--- End quote ---
Maybe it's a good idea to install one extra head mount, on the front of the engine. Just in case. Then always investigate the suspicious parts on cracks after riding the KX5.
I have done some research. Know your point know. But besides, the alloy is often used in the aircraft industrie, and there are also welded mountainbike (or other bicycle) frames made of this alloy. 7075 has good properties of tensile strenght and dynamic tensions. But if I understand you the right way, there is a chance the combined alloys can provide stress in the material, which can lead to cracks (stress corrosion cracking).
If I make an extra head mount, the suspicious parts can fail by cracking, but the chassis will stay together. Or al the four points (now it has three points) of mounts has to fail at the same time.
When i have some time, I wil make an extra Y part, made of another alloy. So when it's neccessary I can replace the Y part easily, it will take me a few hours to re-weld the frame when the engine and the other parts are removed.
Very interesting case... I'm curious about how the frame will stand under charging the KX5.
motopunk:
that was one of the reasons to make my steel-frame-conversion... the 2. was that i had this frame laying around and realy like the ergonomics of the 93 kx 250 ... 3. the aluminium-welding is little bit more dificult than on steele and 4. nowhere was an aluminium-framed bike with a blown engine to find...
but if i will find an al-bike i plan to build the worlds first kx360af ... 8-)
hulkteam476:
Hi,
The ideal (or the best, I used this) for me is, alloys 6061 t6... or (6063)...better flexibility...
simply, the 7075 is realy rigid. Good aplication for to make the linkage or triple clamp but,
too rigid whit the other part of you'r frame.
THX..
Jos197AF:
--- Quote from: hulkteam476 on March 26, 2014, 10:53:38 AM ---Hi,
The ideal (or the best, I used this) for me is, alloys 6061 t6... or (6063)...better flexibility...
simply, the 7075 is realy rigid. Good aplication for to make the linkage or triple clamp but,
too rigid whit the other part of you'r frame.
THX..
--- End quote ---
Too rigid? The E modulus of 6061 is 69 GPa, the E modulus of 7075 is 71 GPa. Not a big difference.
I think too rigid is not the problem. 7075 contains more zinc and magnesium. Stress corrosion cracking is the issue to watch out for.
Applications 7075: aircraft fittings, gears and shafts, fuse parts, missile parts, regulating valve parts, wormgears, keys, aircraft/aerospace/defense applications, bike frames, atv sprockets
hulkteam476:
You know I told you this but you do whatever you want my friend.
Just, as you passed spectrometer, your original frame?
I say "simply" not to go into details.
In addition be warned that you have the machined part (7075) in full.
The 7075 does not manage at all the same constraints: bending, vibration ... compared to the 6061 or 6063... for this application. You also have to know that the 6061 is much better for welding performance and is also used in aeronautics.
This said, you were right to try. After testing you can give me your feedback.
Thx
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