2001 Bi-Metal Planchet Australian 20c
In July 2007 a 2001-dated 20c piece struck on a bi-metal planchet was sold in Downies auction 295. It was reportedly found in an Armaguard roll. The piece was struck on a planchet with a gold-coloured outer rim with a silver-coloured core and it weighed 10.66g: not only was the planchet the wrong colour, it was a little under the designated weight of 11.31g (p124, McDonald, 2014 Pocket Guide to Australian Coins and Banknotes, 2013).
A second example of this error was shown on Facebook at some point in 2017 (p10, Andrews, Errors and Varieties in Australasian Coin and Banknote Magazine, September 2017). It was sold in October 2017 at Downies auction 325 as lot 1785.
The Royal Australian Mint source planchets from Poongsan in South Korea. The company produces planchets for many countries and their standards are high: contamination of even a single wrong planchet is rare, let alone multiple. Nevertheless, at least two bi-metal planchets were shipped to Australia along with millions of other 20c planchets at some point in 2000 or 2001.
The true destination country for the bi-metal planchet is believed to be Iran for the 250 rials (Nemtsas, Error Coin Spotlight - 2001 20 Cent Struck on Bi-Metal Planchet).