I admit that 6082 is not an alu alloy that I'm very familiar with. Most of my dealings were with 6061 and 6005. So please everybody double check my comments.
What I do know now, after checking the specs, is that 6082 has a much higher ultimate and yield stress levels then the other commonly encountered alloy types. While maintaining the same desnity and stiffness. So thanks for the heads up Grob.
However with beach cats only a certain minimal value of yield stress level is required for beams. In effect, any additional yield stress beyond a certain level does not improve the boat design in any way because other factors like minimal wallthickness and extrusion considerations prevent optimal use of the higher level.
In my dealings so far, all alu alloys with tempering above 200 MPa yield stresses were well suited to cat beams, booms and spi poles. But if I'm mistaken in this then I welcome anybody saying so. I'm always open to learn new stuff.
I just read that :
It is difficult to produce thin walled, complicated extrusion shapes in alloy 6082. The extruded surface finish is not as smooth as other similar strength alloys in the 6000 series.
So the guy offering you the 6063-T6 as an alternative to 6082-T6 may still have given you good advise as for example a 80x2 mm beam of either material will behave exactly the same in 90 % of the possible applications. The only exception being the really highly stresses situations where the amount of associated flexing is not a limiting factor. In catamaran beams however it is the flexing that is one of the main considerations, as a result the cat beams tend to be overdimensioned and under stressed. If the latter is the case then the 6063 material could be cheaper and have a better surface finish for the same performance.
6005-T5 is interesting for the following reasons :
source ;
http://www.aalco.co.uk/technical/datasheets/Aalco_Datasheet_Al_Alloy_6005_6005a.pdf
Aluminium alloy 6005/6005A is a medium strength, heat treatable alloy with excellent corrosion resistance. Alloy 6005 has properties between those of alloys 6061 and 6082 and can sometimes be used interchangeably with these alloys, but 6005 has better extrusion characteristics and a better mill surface finish. It is difficult to produce thin-wall or complicated extrusions in 6005, but it is still more extrudable than 6082.
It was also advised that 6005-T5 suffers less from shape distortion during the heat treatment then 6061-T6. Note that the code T5 also indicates a slightly different heat treatment proces. Therefor 6005-T5 has certain production advantages over 6061-T6 and I'm guessing over 6082-T6 as well. One of these is that thinner walls can be had with less rejects per production batch.
But the upshot of all this nerding is that all quoted alloy's will be fine if they come in a 80x2 tube. The differences are too small to matter.
Wouter
