Re: What Is Alloy?
- From: nick c <nchen711@xxxxxxxxxxxxx>
- Date: Wed, 09 Apr 2008 15:55:06 GMT
Agent Smith wrote:
nick c <nchen711@xxxxxxxxxxxxxxx> wrote in
IvXKj.17207$4O1.384@trnddc03:">news:IvXKj.17207$4O1.384@trnddc03:
Agent Smith wrote:Does anybody know the name (or names) of the famous alloy from which
high- end racing components are made? :] Whenever I see it referred
to in books and articles, it is just called "alloy," but apparently
there's a whole branch of engineering that's embodied in that single
word, and writers gloss over the whole subject when they say that.
Alloys are chosen or created with the intention to reliably fit the function that engineers planned for in design. My guess is the word alloy is used as representing a variety of alloys suitable for a given
design/application. Example: valves in a high performance engine, be
the valve stems hollow or solid, may be made from 6-4 titanium (heat
treated to 160KSI), while domed piston heads may be made from 6061
aluminum; piston head pins may be made from 7075 aluminum, assembled
on connecting rods which may be forged from 6-6 titanium (heat treated
to 180KSI). Various stainless steel and/or titanium parts may be made
from sintered stainless steel or titanium, where loads are low, below
the limits of sintered material yield. Then there's ceramics ......
(shrug)
I supposed you've already done an Internet search? I'll guess again
and say if you've done a search, you may have found alloys having proprietary designations.
Until you said "7075," I didn't have a keyword to search for, but I googled it last night, and now I've got the details. I would have thought that it was alloyed with nickel, but it turns out to be zinc. Compared to steel, 20+ KSI yield stresses are pretty pathetic, but I guess that it's sufficient for the loads a component is likely to experience in bicycling. I wonder who Campagnolo's suppliers are, for that stuff, and who forges it.
Nickel is not a good alloying agent with aluminum. The zinc content of 7075 aluminum is high. 7075 can be heat treated to a T3 or T6 condition. Usually, 7075 is heat treated to a T6 condition to gain the higher strength yet retains a high modulus of elasticity (roughly, about 10% RA). It has good shear strength properties, not too good at elevated temperatures (roughly about 200 degrees F.) and the copper makes 7075 highly susceptible to stress corrosion cracking when heat treated to a T6 condition. You have to be careful using 7075 at elevated temperatures for long periods of time. Sustained temperatures above about 200 degrees F have a cumulative effect on 7075 material strength. Because of the copper content, I don't recommend 7075 (or 2024 alloy) be welded. Welding will degrade the alloy's corrosion resistance.
6061 aluminum alloy has lower mechanical properties than 7075 0r 2024 but it can be used at higher temperatures (roughly, about 500 degrees F.) and is weldable. 6061 has less zinc and copper than either 7075 or 2024.
You mentioned material yield strength. The SS curve of aluminum alloys is plotted to a 0.2% off-set yield (PP yield will be about 5% to 10% lower but that yield will be unreliable), which is the same off-set yield used for steel. Aluminum is unique in that manner since copper, zinc, magnesium, and other soft alloys are plotted to a 0.5% off-set yield. I don't remember what the yield of 7075 T6 condition aluminum is but I think the 20+ KSI you mentioned is what you get when 7075 is heat treated to a T3 condition.
Now that you have an overview of principle aluminum alloys, it's time for the nitty-gritty. If you intend to use an aluminum alloy to make a bicycle frame, I would think 6061 would be the choice of alloys. 6061 is known as a marine alloy 'cause it has a high level of corrosion resistance and it can be welded. Of course, if you're a 500 pound knuckle-dragging ape ..... oops.
Well ...... I've done too much thinking for one day. Time to fire up my pipe and pallabber with the resident memsahib out in the patio.
.
- Follow-Ups:
- Re: What Is Alloy?
- From: Agent Smith
- Re: What Is Alloy?
- References:
- What Is Alloy?
- From: Agent Smith
- Re: What Is Alloy?
- From: nick c
- Re: What Is Alloy?
- From: Agent Smith
- What Is Alloy?
- Prev by Date: Re: Let's Make Shock Videos Illegal
- Next by Date: Re: Crocker/Patraeus Wrapup
- Previous by thread: Re: What Is Alloy?
- Next by thread: Re: What Is Alloy?
- Index(es):
Relevant Pages
|
