Aluminum: Copper-free and 3.5% Copper

What is the application? Is this structural aluminium alloy, boat hull aluminium alloy, etc. What other alloying additives are there, etc. Do you know the different designations of the alloys?

For example......

http://www.youboat.net/DIY/metalBoats/aluminumAlloys.aspx

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

He's trying to make a light weight cutlass that'll keep the edge of surgeon's scalpel. A fine tool for any boarding party this side of Davy Jones' locker.

Homework?

Nah, this here is Lyle Lovett, and I'm gonna build me a boat and haul a pony around in it.

Yeah, I know the usual marine alloys are 5086 plate, along with 6061 and some 6063 extrusions.

I forget where the copper-bearing (2000 series) idea come from, but it ain't usually mentioned for marine use.

Of course, this depends on what "offshore" means, as in which direction--further out to sea, or further inland?

LL

2000 series can be nice to work with, but copper content is thought to promote corrosion.

Everyone is beating around the bush. The difference is the presence of copper.

Now what this difference will mean to how this gets applied will depend on how it is applied.

In cast aluminum alloys the alloys having 3 to 5% copper do not have as good corrosion resistance as do the low copper or copper free alloys. The 319 alloy has 6% silicon and 3.5% copper and is less corrosion resistant then 356 which has 6.5% silicon and 0.2% copper.

The best corrosion resistance aluminum alloys tend to be the mag-alum alloys like 514 and 535. These have like .05 to .1% copper and 4 to 7% magnesium.The 713 alloy which has about 0.6% copper and 7.5% zinc is rated better than the 319 alloy and about the same as the 356 alloy.