Identifying pop rivets - monel or aluminium?

[KompetentKrew]

Obviously I could just go out and buy the right ones, but I have here a small box of pop rivets that came with the boat - I hate waste and for my own education, is it possible to determine what they're made from, please?

It's for holding together the two halves of my bimini - this is obviously stainless steel and I think monel would therefore me more suitable than aluminium.

Thanks for your time.

 

[DownWest]

All look like ally. When you see the price of monel, you don't leave them lying around! Also, monel have a slight bronze tinge to them.

 

[wilkinsonsails]

Ally ones tend to have steel pins ,try a magnet on them . Those look like Monel .

 

[VicS]

Ally ones tend to have steel pins ,try a magnet on them . Those look like Monel .

Monel rivets can have steel mandrels too

 

[PlankWalker]

Bite em hard, if your teeth dent them there ally. if you break your teeth there not!

 

[NormanS]

Try a file on them.

 

[AngusMcDoon]

Pop each one in turn. If it pops easily, put it in a box marked aluminium. If you have to huff & puff & strain & grunt, put it in another box labeled Monel. Simples!

 

[KompetentKrew]

Bite em hard, if your teeth dent them there ally. if you break your teeth there not!

Try a file on them.

So if I can scratch them with a hacksaw blade (I wouldn't trust any of my cheap rusty files) it's aluminium; if no mark is left it's monel?

Thanks all.

 

[VicS]

So if I can scratch them with a hacksaw blade (I wouldn't trust any of my cheap rusty files) it's aluminium; if no mark is left it's monel?

Thanks all.

I think a hack saw blade , or even a rusty file, will be harder than Monel

 

[John the kiwi]

Interesting problem! Normally i can tell mine apart as aluminium is brighter than the monel, but from your photos its hard to say if they are monel or aluminium that has had a hard storage life, so i went to my workshop and experimented.
Yes a file or hacksaw will demonstrate a difference. I found that giving a gentle calibrated squeeze with a pair of side-cutters made it easier to distinguish, but i think it may be difficult if you in fact have all monel or all aluminium and nothing to compare with.
In this case drop them in a strong caustic solution and leave them overnight. Any that you have left after this treatment will be monel.

 

[vyv_cox]

Don't forget that there are (at least) two grades of aluminium pop rivets. The cheap ones sold almost everywhere are 1xxx grade, almost pure aluminium. The better ones used by spar makers are 5xxx, far better corrosion resistance in marine environments.

The better ones seem to be named 'aluminium alloy' in some outlets, e.g. RS.

 

[Neeves]

I thought most of your rivets were aluminium, signs of surface corrosion, apart from a few that looked like stainless. The stainless ones looked bright and shiny - and might look more shiny with a gentle wipe. The aluminium ones looked tired and dusty - none looked like Monel. One, that long one, looked like stainless and was so long I wondered where you envisaged using it.

John the Kiwi has a bright answer - keep Monel, aluminium and stainless samples and use them as a comparator. 'Wipe' with a sharp knife, using only the weight of the knife and compare the scratch. Vyv has a similar test (his ball bearing test) to compare tensile strengths of steel (or any metal - I've used it for aluminium and steel).

Jonathan

 

[Poignard]

Deleted. I was going to offer advice but Neeves has already offered it.

[Memo to self: Read previous posts before posting!]

 

[LadyInBed]

Similar to the file method, I would rub them against a wire brush disk in an electric drill and compare the scouring.