Which Metal Alloys Used for Euro Coins ?

On January 1st, 2002 the euro became the single legal currency in twelve European countries; since that date, several other nations have also joined the European monetary union, and have adopted the euro as their official currency. Euro coins are minted in eight different denominations: 2 and 1 euros, as well as 50, 20, 10, 5, 2, and 1 cent euros. Each coin has a common design on one face, whereas the reverse face design is one of several chosen by the monetary union countries. 

In deciding which metal alloys to use for these coins, a number of issues were considered; most of them centered on material properties.

1. The ability to distinguish a coin of one denomination from that of another denomination is important. This may be accomplished by having coins of different sizes, different colors, and different shapes. With regard to color, alloys must be chosen that retain their distinctive colors, which means that they do not easily tarnish in the air and other commonly encountered environments.

2. Security is an important issue—that is, producing coins that are difficult to counterfeit. Most vending machines use electrical conductivity to identify coins, to prevent false coins from being used. This means that each coin must have its own unique “electronic signature,” which depends on its alloy composition.

3. The alloys chosen must be “coinable” or easy to mint—that is, sufficiently soft and ductile to allow design reliefs to be stamped into the coin surfaces.

4. Also, the alloys must be wear resistant (i.e., hard and strong) for long-term use, and so that the reliefs stamped into the coin surfaces are retained. Of course, strain-hardening occurs during the stamping operation which enhances hardness.

5. High degrees of corrosion resistance in common environments are required for the alloys selected, to ensure minimal material losses over the lifetimes of the coins.

6. It is highly desirable to use alloys of a base metal (or metals) that retains (retain) its (their) intrinsic value(s).

7. Alloy recyclability is another requirement for the alloy(s) used.

8. The alloy(s) from which the coins are made should also provide for human health—that is, have antibacterial characteristics so undesirable microorganisms will not grow on their surfaces.

Copper was selected as the base metal for all euro coins, inasmuch as it and its alloys satisfy the above criteria. Several different copper alloys and alloy combinations are used for the eight different coins. These are as follows:

Value	Image (2007 - present)	Main Colour		Secondary Colour		Diameter (mm)	Thickness (mm)	Mass (g)	Shape	Composition	Edge
€0.01			Bronze		None	16.25	1.67	2.30	Round	Copper-covered steel	Smooth
€0.02			Bronze		None	18.75	1.67	3.06	Round	Copper-covered steel	Smooth with a groove
€0.05			Bronze		None	21.25	1.67	3.92	Round	Copper-covered steel	Smooth
€0.10			Gold		None	19.75	1.93	4.10	Round	Nordic gold	Shaped edge with fine scallops
€0.20			Gold		None	22.25	2.14	5.74	Spanish flower	Nordic gold	Plain
€0.50			Gold		None	24.25	2.38	7.80	Round	Nordic gold	Shaped edge with fine scallops
€1.00			Silver		Gold	23.25	2.33	7.50	Round	Outer part: nickel brass Inner part: Layers of copper-nickel, nickel, copper-nickel	Interrupted milled
€2.00			Gold		Silver	25.75	2.20	8.50	Round	Outer part: copper-nickel Inner part: Layers of nickel brass, nickel, nickel brass.	Edge lettering, fine milled

2 euro coin: This coin is termed “bimetallic”—it consists of an outer ring and an inner disk. For the outer ring, a 75%Cu–25%Ni alloy is used, which has a silver color. The inner disk is composed of a three-layer structure—high-purity nickel that is clad on both sides with a nickel brass alloy (75%Cu–20%Zn–5%Ni); this alloy has a gold color.

1 euro coin: This coin is also bimetallic, whereas the alloys used for its outer ring and inner disk are reversed from those for the 2 euro.

50, 20, and 10 euro cent pieces: These coins are made of a “Nordic Gold”alloy—89%Cu– 5%Al–5%Zn–1%Sn.

5, 2, and 1 euro cent pieces: Copper-plated steels are used for these coins.

Reference:

http://www.ecb.europa.eu/euro/coins/common/html/index.en.html

Book: Materials Science and Engineering William D. Callister, Jr