marine grade aluminium

[Howburn]

Hi,
Have had a customer ask for some marine grade aluminium, I have never heard of it. Spoke to Thomas Grahams in Carlisle, who in turn spoke to both some of their suppliers and customers involved with ship/boat building and they are unable to source it, TG did tell me it is better known as 5086 grade but again this means little to me.
Can anyone explain in greater detail? And also does anyone know where to get some? About 20’ by 2”X1/8”. Preferably in Cumbria.

 

[Paul.]

I've been asked for it occasionally for machine frames used in wet areas, 5083 or NS8 is what we came up with, but its only available in plate, for sections the next best corrosion resistance is one of the 6063 variants or HE9, or probably more available 6082, HE30, which is available in sheet and extruded sections,
for the applications I'm involved in I usually talk them round to using stainless nowadays.

 

[Drains]

Howburn, take a look at this

http://www.seaotterboats.co.uk/english/aluminium.php

and this

http://www.solsteel.com.au/Alloys.htm

Should give you a start. Si.

 

[TechnicAl]

Ive always known 5083 to be called Marine grade. Its certainly resistant to sea water corrosion. It should be welded with 5183 filler but 5356 will be OK.

 

[hotrodder]

Aluminium alloy and temper designations, properties and a bunch more... http://aluminium.matter.org.uk/aluselect/default.asp
5183 data sheet which expands a little on what Al said

As said extrusions/sections (like 2" x 1/8" strip) are generally only available in 6063 and/or 6082. Standard length is usually 5 metres

 

[strider33]

I do a lot of sailing, but I've always understood Ali to require anodising to be properly "marine". It is possible to use a specialist paint to recoat it if the anodising has been worn off, but I've not used it.

 

[Drains]

The great majority of boats in New Zealand- from sailboats to workboats to ferries to 200ft fishing boats - are from aluminium, as it's so cheap there (cheap hydro power for the smelters). They don't have problems with it, and I'd love to see you anodise the welds after fabrication on a 200ft boat (you can't weld anodised ally).

Aluminium's poor reputation for sea-work comes from the post WW2 era, when surplus or scrap aviation aluminium was used in boats, with poor results. I know old folk who won't touch the stuff, but that's because they're stuck with memories of 50 years ago.

 

[hotrodder]

FWIW there are techniques for welding anodised ally, typically known as 'bump welding'. A few articles on the subject...

http://www.thefabricator.com/article/arcwelding/mastering-gtaw-of-anodized-aluminum
http://www.millerwelds.com/resources/articles/anodized-aluminum-AC-TIG-GTAW-welding-Birdsall
http://www.fandmmag.com/online/article.jsp?submit_comment=y&id=67&pageNum=1#commentform

Not really practical for building a hull but typically gets used for tubular products (6xxx series) especially those that are too big to be anodised after fabrication

 

[Drains]

Good links hr - we live and learn. I wish I'd said "you can't weld anodised aluminium easily"!

 

[hotrodder]

Yeah, i suspect it takes a hell of a lot of practice to get to grips with that technique and get consistant, sound welds on anodised Al