Aluminum alloy determination

[anontrolus]

Does anyone know of an easy way to determine the exact alloy of aluminum one is working with either through limited destructive or completely nondestructive techniques?

I need to know what type of welding wire and stock aluminum to purchase.

Thanks in advance....

[noelex 77]

Not sure if it will be any help, but if it's a boat, aluminium from reputable suppliers will be labeled with the aluminium type.
Below the waterline is generally not insulated or painted and if you poke around you should find a stamp somewhere with the aluminium type. My boat has severalsuch stamps from the original producer of the aluminium.

Destructive testing must be possible as I have seen forensic examination of boat structures.Notably in about 1996 when there was a defective batch of 5086 produced with some very expensive court cases where the alloy was shown to be the wrong composition for 5086.

However I would imagine such testing would be very expensive.

Generally substituting a suitable marine alloy is acceptable. The alloys are so close on the galvanic scale that there are no practical problems.

Most aluminim boats use different alloys for the extrusions (typically 6 series) and the plate (5 series) without any problems.

[Lagoon4us]

If you strike 5083 or 5086# (that's not annealed) with a metal bar it rings plate is usually 5000 series and extrusions 6000 series with silicon to assist the extrusion process.

Really need to keep tabs on origin to be sure..'Tis a hard one!

[Lagoon4us]

Also the higher the magnesium content the more spatter balls you will see burning whilst you weld....5000 series is safe with 5%mag whilst castings 5 to 10% silicon....