"Marine" grade Aluminium

[Yellow Ballad]

I've bought myself a small lathe and mill to have a play with and obviously there's lots of boat bits I would like to have a go at machining.

Probably a question for Vyv but what would be an ideal grade to use?

6082-T6 seems to be the go to in the model engineering world but 5086-H8 seems to be talked about for marine use (and ability to weld). I know, there will be different grades suitable for different applications but any general rules, pros and cons?

At the moment on the project list are spares for my roller boom (gooseneck) and a spinnaker car for a friends 32mm track (as he's had quotes for around £800!) to give you an idea.

Tom

 

[vyv_cox]

6082 T6 is heat treated for improved strength. If you can buy it in a large enough section for the jobs this is probably the one to go for where corrosion resistance is not of utmost importance relative to strength.

5086 has better corrosion resistance and is used for hulls but is not heat treatable for strength. Cold worked base stock may be available, I have never looked, but again section may be limited.

 

[earlybird]

6XXX series bar is the type most readily available it would seem. I've machined mast halyard sheaves from it, 'cos that's what my local metals supplier stocks. It machines readily to a good finish and there were no corrosion problems.

 

[Yellow Ballad]

Great, thanks both.

 

[Neeves]

I believe 5083 is a common marine grade aluminium alloy - and I thought used for the hulls of aluminium runabouts.

The 7xxx series is used for rock climbing kit (because it has a high tensile strength, but lacks some corrosion resistance against seawater. I believe 7075 is used in LFRs - but it is supplied to the consumer anodised. 7075 is used for the shank of my aluminium Excel anchor - the anchor is now around 10 years old and the shank still looks reliable (its not anodised). I made a bridle plate from 7075. it corroded as I watched - in contrast to the shank and I think maybe I contaminated the bridle plate in some way. I have anodised 7075 - and it has not corroded - so a bit of a puzzle. 7075 has very low yield, has no elasticity, and snaps like glass - so be careful with your designs.

I think if you are going to work with aluminium, and put some effort into it, then you need consider home anodising - its not difficult (but I cannot get to grips with coloured anodising). Now - I would not consider making anything without anodising, otherwise your efforts may dissolve. I'd watch mixing metals and I'd watch what equipment you use that may inpregnate (contaminate) the item and cause preferential corrosion. Lots of anodising lessons - YouTube.

Lots or armchair experts who have never actually used many of the alloys.

I'm n o expert, I'm learning by my mistakes.

There are some interesting Lithium based alloys (aerospace) with high strength - not yet used as far as I know - in focussed marine applications. Expensive (as is 7075).

My conclusion is - there is no best alloy - there are horses for courses, but you can buck the theory by anodising. Play with it, them - but don't offer warranty until it has been tried - in real life. Bear in mind that experience with some alloys is large scale (an aircraft wing) which might be slightly more difficult to anodise than an LFR.


Jonathan

I forgot - also consider there is a relationship between tensile strength and hardness, the stronger the alloy the harder. It has not been a feature of anything I have done but machining might be more difficult if the alloy has high tensile strength.

 

[Wing Mark]

I would completely agree with Jonathan about anodising.
Bare aluminium is just an anode for any stainless screws which go near it.

I've made a few bits with a mini-lathe and a small mill (also hammers, files, black and decker...), the best materials to use are often a) what's easily available and b) stainless and c) plastic.

I've done a few (non-yacht) bits made by laying up a bit of carbon fibre then machining it. (be afraid of the dust!!!)
A few sheaves, spacers, rollers etc from delrin/acetal/POM

But half the time I fire up the lathe it's pretty unexciting stuff like turning down the head of an M4 mushroom head allen to replace the derailleur adjuster screw on my pushbike.