Material advise needed 1

[KR1]

Hi,
I'm in the process of building a heavily modified, somewhat experimental, motorcycle. (two stroke)
I have the machining know how but am a bit confused by the material choices open to me.
I need to know what would be the best type of billet aluminium for the following applications & what heat treatments, etc, if any, these would require;
1) top & bottom fork yokes & fork bottoms / caliper mounts.
2) brake calipers (would the bores need special treatment?)
3) crank cases
4) barrels (I intend to have these nicasil plated)
I have looked into it & noted the materials a few aftermarket companies are using but don't know if these are best or how they have been treated.
Hope you guys can help.
Thanks.

 

[LJW]

I have made many of the parts you listed from a 7075 aluminum called FORTAL. Great material to work with! See:

http://www.mousebar.com/fhome.html

 

[KR1]

Thanks LJW,Fortal looks like it'll be good for stuff like the yokes & fork bottoms. Anyone else got any ideas on the other issues, ie calipers, barrels, etc & best treatments?
If not, any ideas for further reasearch?
Cheers.

 

[EngJW]

Another workhorse in the aluminum family is 6061-T6. It is for machined parts only. Castings are typically 356 or 355. Usually the foundries will have a lot of say in what they will pour. Sheet metal comes in certain grades but I can't help much on that. The supply houses could tell you what is available.

 

[KR1]

Nice one, thanks fellas.

 

[LJW]

KR1,
I'd like to hear more details of your project.

 

[KR1]

LJW, Engine wise I'm working on updating an old 'uniflow' two stroke design & building it with modern materials & tolerences to early 90's tuning levels. I got the inspiration from KG Draper's 1978 re-print of 'The Two Stroke Engine, Design & Tuning' (published by Haynes)& the huge pile of KR1 250 parts I had kicking around. The rest of the bike will be built with similar 'alternative' technology re-applied.

 

[CNGBrick]

Have a good look at MIL-HDBK-5 before using 7075 aluminum alloy in a critical structural application. Its mechanical properties in the T6 tempers are directional, especially with regards to stress corrosion cracking (a concern if there is any chance the part may be exposed to salty water [such as road salt]). It could be risky to machine a part without knowing the direction of extrusion or rolling.

RT

 

[KR1]

All sounds a bit worrying/expensive,
would stress relieving heat treatment
not eliminate most of these problems though?
Anyone know anything about H30? I've noticed
a few companies using it, is it any better?

 

[CNGBrick]

KR1,

I understand that heat treating 7075 to a T7 type temper may alleviate the tendancy for stress corrosion cracking. I don't know of the effect on the other properties though. Try contacting one of the big aluminum producers or posting in one of the metallurgy forums for an application recommendation from a metallurgist. They have a lot of information that doesn't show up on the typical data sheet.

RT

 

[swall]

CNGBrick's advice is well taken. The use of 7075-T6 in a corrosive environment is a big no-no due to stress corrosion cracking (SCC) concerns. With a fork triple tree clamp, you would have an ideal SCC specimen 180 degrees from the fork tube pinch bolts.The T7 tempers alleviate this concern to an extent, however, if you read the footnotes in the Aluminum Association book, it is stated that the improved SCC rating comes from a 30 day test at 75% of yield strength in the short transverse direction. Yield strength of 7075 goes from 68ksi min in the T6 condition to 57ksi min in the T73 condition and 75% of that would be 43ksi. Not much better than 6061-T6. Also consider that most of 7075 is used in aerospace applications and is almost always given supplemental corrosion protection.

 

[KR1]

That all sort of leads us round in a circle.
I appreciate that there is never a 100% ideal material for any application & I really appreciate your input, so I've decided to re define the question a bit, if that's OK with you guys?:

What type of billet aluminium would be best suited to machining into motorcycle yokes, bearing in mind;
-They are a one off, being made in a home workshop.
-They only need to perform as well as standard japanese race rep yokes, although better (ie World Superbike sort of quality) would be nice.
-I could get them heat treated, annodised, etc if necessary.
-It would be easier not to have to worry about grain direction as I'm still confused by it;
If you were facing the bike from the front, looking straight at the yokes, should the grain run left to right, up to down, or front to back?

Cheers for sticking with this one fellas.