Actually, aluminium alloys don't change much at all in the way of density and stiffness from one alloy to the next. That is when looking at alloys with relatively good corrosion resistance and good extrusion behaviour. Most significant differences from alloy to alloy are to be found in the ultimate (break) stresses. However this is not really an important factors in beams, boom or masts. In these components one is far more interested in the amount of stiffness one can get for a given weight. Yield stresses don't seem to dependent on the type of alloy, they are however very dependent on the applied temper (T-codes). This is an after (heat) treatment that improves certain specs.

so

6061-T6
6005-T5
and
6082-T6

are what you are looking for.


Note that the T codes ARE important as these have a VERY big influence on yield stress. This is the level at which a tube will not break but maintain a permanent bend after being overloaded. In boat design we want all components to straighten out after we remove the (peak) loadings. So a minimumal level of yield stress should be maintained.

Having said all this I have not encountered any supplier that delivered 80x2 mm tubes of any other specification then the ones above. 80x2 tubes are clearly structural components and they use structural alloys when producing them. But guys like Hans have bought and sold much more alu tubes then I have and so they should be able to much better inform you here.

Otherwise follow these links for more info :

http://en.wikipedia.org/wiki/Aluminum_alloy

http://en.wikipedia.org/wiki/Tempering

http://www.aalco.co.uk/technical/datasheets/Aalco_Datasheet_Al_Specifications.pdf


More general sites with specs :

http://www.aalco.co.uk/technical/aluminium.html

http://www.azom.com/materials.asp

can someone post these comments on our open source F16 design wiki ?

Good luck,

Wouter