Alu frame - what grade alu?

[I am Spartacus]

Metallurgy is not my strong point, but are there not varying grades of alu used in bike frames?
Which is the lightest and how can you find out what your bike has?
Anyone know?

 

[very-near]

The strongest grade of ally is 6082 (aircraft & ally ladder sections). The extruders use 6063 from window frames and low stress applications. My Marin is 7005 grade (sticker says so on the saddle post) and the T6 is the grade of temper which sets the grain characteristics which is done by quenching with big fans or water curtain as the profiles exit the extrusion press.

It isn't just the grade which determines the strength, but the quality of butting and welding at the joints.

If you look at the manufacturers websites, all this info should be there.

 

[accountantpete]

You won't be able to tell how "good" a bike is from the grade(s) used in a frame. As VN says ,the butting and welding are key especially in delivering a stiff bottom bracket as is the geometry of the bike.

 

[I am Spartacus]

So the frame builder can use the lightest grade but must pay attention to top notch welding etc?
Apart from a visual check of tidiness, you have to take strength on trust?

 

[jpembroke]

what are you looking for? MTB or Road frame? If it's a road frame, I recommend the Planet X Superlight Team frame. That's 7005 T6 alloy by the way.

 

[I am Spartacus]

I is interested in the Boardman Team alu.. it is very very light , almost as light as the Team Carbon

 

[very-near]

I is interested in the Boardman Team alu.. it is very very light , almost as light as the Team Carbon

We have a customer in Saudi who extrudes tubing/profiles down to 0.6mm in wall thickness. It is very problematic though as it is difficult to handle (distorts under its own weight when hot) and is very difficult to squeeze through the Die (breaks the dies as they collapse under the pressure, and the forming surfaces overheat due to the enormous friction of a 2500 tonne press squeezing it out)

 

[G-MAC]

I should imagine the SCANDIUM alu frames are the lightest. There should be a frame sticker or badge saying what type of alu you have.

 

[TheDoctor]

There's no real difference in density between any of the grades of aluminium, it's the wall thickness and butting that reduces the weight of a frame. My cheap-and-cheerful plain gauge Ribble frame weighs about 1.4 kilos, and I think Scandium butted frames can go down to just under a kilo. But that's because there's less metal, not because the metal is lighter.

 

[rogerzilla]

The first ones were 6061 because that was what was available. It needs post-weld heat treatment (i.e. the whole frame has to be heat treated). Then 7005 became more common, because that doesn't need any treatment after welding (and also means repairs are theoretically possible, although most people would junk a broken alu frame).

Apart from cheapness, aluminium doesn't have a whole lot going for it in the age of carbon fibre (for ultimate performance) and super strength steels (for later adaptability and bespoke options). Titanium is corrosion resistant, of course, but I've never been convinced it's the ideal material - just something that was a bit lighter than steel at the time, and suddenly became plentiful with the end of the Cold War.