The curious 'life' of a rivet

Having had a mis spent youth as an aircraft apprentice at Weybridge 1963 - 1968, it was my practice to grovel under bits of aeroplane under construction and pinch anything that had dropped onto the floor - amazing what you could find.

Amongst my finds were quite a few rivets, all colour coded. From what I remember, black was soft aluminium, mauve was a little harder and used for most joints, however there were self coloured and green rivets. These had to be annealed before use and had a 'short life' before they age hardened. So much so, that these rivets had to be drawn from stores in coloured pots, and each coloured pot had a life of about 6 hours. If you were caught using the wrong coloured pot outside of its 'life time' you could be dismissed. Does anyone know what the annealing / precipitation process could have been, as these 'hard' rivets tend to crack if set in the hard state. They were obviously an aluminium alloy of some sort

As an aside, all (dry) panel joints had a yellow anti scuff / corrosion treatment whereas wet (Fuel) panels had a short life Thyacol mastic applied - a devil to get off your clothes, but super for mending old car fuel tanks.

They're often an aluminium/copper alloy, eg 2024. The rivets are solution heat treated before use. This involves heating, soaking at temperature, and then quenching in cold water. This forces the copper into a solid solution. Over time, usually days, the copper migrates out of solution and ends up on grain boundaries, making the rivet harder. This is age hardening.

The yellow/green finish is an etch prime, used to be zinc chromate based, but there are chromate free products available now. I'm pretty sure we used to use a zinc chromate goo when assembling steel fittings into wooden aircraft, to prevent corrosion.

Regards,

Andrew

As I remember we used to use a lot of mauve coloured rivets when making equipment boxes riveting the box panels to a cast alloy frame. We had to coat the rivets in a soap and then heat until the soap went a brown colour, the rivets were than OK to use in the normal way.

Kwil, the soap treatment is the norm for annealing aluminium , also used if you want to make an aircraft skin with a compound curve, soap, heat till brown, form curve, leave a few daysand it's hard again, used to help a helicopter engineer, rebuilding, and making new skins. Ian S C

Edited By Ian S C on 23/11/2012 09:07:37

I have a mixed tin of those colour coded ali rivets. They came from a chap who worked with spitfies in Hursley Park during the war. Do you think that they will need annealing now?

Frank