Alloy or aluminium?

[Drago]

In actual practice there's very little difference between 6061 and 7005. Tube manipulation and butting will be the deciders

 

[Cubist]

denser metal alloy does not mean stronger - just think how strng a bike frame mdae from lead would be!!!!
there'd beo ther reasons why the 7005 is stronger and I doubt it is due purely to density.

No, of course, but a denser grained metal can be drawn thinner for the same strength tubing, all other factors being equal, which is why tubes made of 853 Reynolds are lighter than 661 Reynolds tubing for the same diameter, but just as strong.

 

[albion]

Cheap bikes use 6061 whilst strong hybrids stick to 7005.

7005 frames nearly vanished but its making a bit of a comeback.

 

[Gravity Aided]

6061 T-6 has magnesium and silicon as its alloying agents, and it's ability to withstand shocks and such can be positively or negatively enhanced by loading, gradient, and surface finish, which means that design workmanship, and quality of finish should be quite important in your considerations, as should weld quality. Look for gaps and poor weld finish, as these may have some effect on the overall longevity of the bicycle. I would also consider dropout design very important, as these are integral to the frame and subject to failure in extreme situations. I have seen a few pictures from the more mountainous and hilly areas of Southern Illinois of a fellow who has had some failures on aluminum frames, but he is heavier rider, and some of the trails there can be rather extreme.6061 has a density of 2.70 g/cm³ (0.0975 lb/in³). 7005 has a density of 2.78 g/cm. Its ability to air temper may lead to stronger material, but it is also favored due to its greater ease of welding. Either of these aluminum choices have the proviso that finishing, craftsmanship, and care are very important in the success of the end product. Steel alloys are easier to manufacture and repair. 4130, 4140, and 4145 are alloys often used by bicycle makers. These materials can be case hardened by the presence of carbon monoxides or the use of charcoal in a case, or hardening pack, which infuses these elements into the surface of the softer steel. You could harden all the way through, but this may make the steel brittle, so hardening the exterior is best, giving the best of both worlds for what the steel alloy has to offer.Craftsmanship makes a difference in weight and repair-ability. Last week, I traded in a complete Cannondale H600, weighing 24 pounds built, and 6061 aluminum. I received in exchange a Fuji Touring Series IV frame and fork, weight built 24 pounds. I would consider both bicycles to be equal in speed, but the aluminum ride is harsher. Things can be done to mitigate this, like an alloy fork, but it is still a better ride on steel. For a mountain bicycle, with an emphasis on durability, I would prefer steel, due to its more forgiving nature and repair-ability, given the stresses involved. Fracture lines along the dropout edges and stress points may also appear with age. Steel bends, aluminum can crack instead.

 

[Drago]

Cheap bikes use 6061 whilst strong hybrids stick to 7005.

Poppycock. The only thing 'higher' about 7005 is the number. They're different approaches to the same problem and, as Mr Aided points out, manipulation, build and the heat treatment process used are the real deciding factors.

You will find plenty of excellent frames using both materials, and plenty of dreadful ones.

 

[albion]

They switched to 6061 for cost.

http://www.makeitfrom.com/compare-materials/?A=6061-T6-Aluminum&B=7075-T6-Aluminum

As you can see they are chalk and cheese.

 

[Drago]

And the raw material is cheaper. So what?

And that data is for just that, the raw material, not the heat treated finished product. Depending on the heat treatment technique/cycle applied there's not a lot in it, at least not enough to justify pub smugness a la 853 v 501.

 

[albion]

There a heck of a lot in it., and it will be for finished tube. It seems 7075 got invented by the Japanese for WW2 airplanes, and even gets used in guns

I bet all the small workshops in China churn out 6061 because they can easily get it right.
But even then all those welds will likely need all the heat treating redone.

 

[rojobe]

Has anyone mentioned ride quality? If you're looking for a pure road bike then Alu alloy or Carbon are 99% of the choice. If it's a tourer or more of a do-it-all then steel comes into the frame. Aluminium has no discernable flex so the ride can be harsh and on 23mm tires you'll feel a lot from the road surface. Steel tends to flex and in a good, well designed frame this characteristic can be used to create a ride that is a little more forgiving and comfortable. This becomes more of an advantage over longer distances. So many touring or audax frames are still made from steel.

 

[raleighnut]

However, in bike marketing terms, a steel alloy frame would be billed as steel or chromoly. Alloy is generally used to denote an aluminium alloy. So if @Alan Farroll is in the market for a new bike, he can be reassured that an "alloy frame " is going to be an alu alloy. Very few entry level MTBs are made of steel alloy, and if they are, the marketing will,make sure you know it.

I've been going out a lot more on the trike lately (my leg is getting better) and have been into a few shops to buy bits and pieces, looked at bikes while in there and have seen a lot with stickers reading CrMo Alloy so I would say any frame described as alloy (as opposed to XXXX Aluminium) is in fact a CrMo frame

 

[Gravity Aided]

Some steel bikes may be made of Hi Ten, or High Tensile (Strength) steel, which is a bit more malleable than Cro-Moly. Cro-Moly is better in all aspects, IMO. I think any good bike frame would be made out of 41xx series Cro-Moly, but I also point out that the Trek 800 in its original incarnation was Cro-Moly only as far as the seat tube, and the rest was Hi-Ten. Yet it is a very nice bike, for a bottom of the line model.

 

[Psycolist]

Well, that has turned my perception of Aluminium versus Steel on its head. I always believed the ride of an aluminium frame to be more flexible and pliable than steel or cro-mo. The information given in this thread has been given very clearly and has answered many of the questions that were going through my bonce when reading the first couple of posts. However, when all said and done, IMO, nothing beats the looks of a bare, unpainted aluminium finish on a frame. BUT, after reading this thread, I will certainly not dismiss the possibilities of a steel / cro-moly frame build in the future.

 

[Gravity Aided]

Chromed steel,also pleasing to the eye,but reputedly more brittle. A painted frame may bend,a chromed one may snap,under the same conditions

 

[raleighnut]

Chromed steel,also pleasing to the eye,but reputedly more brittle. A painted frame may bend,a chromed one may snap,under the same conditions

That is due to Hydrogen Embrittlement which can be solved by heat treatment. I think it involves holding the plated component at 170 centigrade for 2 hours.
I'll google it.
EDIT -I'm wrong. it may take 22 hours at 190-220 centigrade to remove molecular hydrogen after plating (and that is in a non-hydrogen atmosphere so not a gas-fired oven.)

 

[Drago]

Nickel plate instead? Does that affect the steel?