A Guide to Marine Grade Aluminum

See below for a handy comparison chart of Marine Grade Aluminum Alloys.
We often get asked which alloy to use, and the answer is “it depends”.
There are three alloys that we generally recommend for hull plating and frames: 5086, 5083, 5052
And two alloys we recommend for extrusions such as flat bar, tee bar, and tubing: 6061-T6, 6063-T52

IMPORTANT NOTES:
In general 5000 series is made into sheet goods and 6000 is extruded; so 6061 sheet is a second consideration of the alloy. 6061 has a higher tensile but the lower ductility means you’d poke a hole in the 6061 hull with less net force than the 5086/5083 hull because it rigidity makes for more puncture and less ‘give’. 5086 and 5083 are the better choice for hull plates.

For railings, if you’ll bend/roll/form curves buy 6063 T-6 which will ‘age’ into 6061 in less than 14 months but breaks less in bending. When you buy it ask to see your supplier’s proof of inventory or you may get OLD pipe, this material has aged and is much more brittle than 6063. 6061 T-6 is very stiff and no good for bending. But that makes it the perfect choice for stiffeners such as stringers, and strakes etc.

If your rails are long slow curves with saddled butt joints like rails on top of posts (?) then 6061 is fine but it can crack at the deck to topside joint if there are hull residual harmonics at certain RPM’s

Brackets, pad eyes, mounting plates and so on, can be cut/drilled/tapped from 6061 bar stock very well, so you won’t have to spend time finding 50 series plates in small quantities.

Radar masts, antenna mounts, railing and other extrusion based fabrications are fine in 6061 unless there is bending / cold forming; then the 6063 is much more forgiving to form, and it will age into 6061 anyway.