Silicon tombac (german: Siliziumtombak) is an

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...

made of copper (80%),

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic ta ...

(16%) and

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...

(4%).

General properties

The silicon content leads to a strengthening of the metal matrix. The appearance is similar to ordinary

brass Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other wit ...

. Silicon tombac has good friction bearing characteristics and is corrosion resistant but is not resistant to

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...

atmosphere. The strength properties are largely retained at application temperatures up to 200 °C.

' Breuckmann It is a special

in terms of the combination of casting process and casting temperature. In most cases, parts made of silicon tombac, are produced through the

high pressure die casting Die casting is a metal casting process that is characterized by forcing molten metal under high pressure into a mold cavity. The mold cavity is created using two hardened tool steel dies which have been machined into shape and work similarl ...

process, which is normally specialized on

metals A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...

with relatively low melting temperatures. But in this case the temperature melting range of silicon tombac is in the area of 950 to 1000 °C, which is relatively high for casting into permanent moulds. The advantage is the productivity of this highly automated casting process. The disadvantage is the temperature stress of the surface of the permanent mould, so that the lifetime of these moulds is limited.

Comparison to investment cast steel parts

High pressure die cast silicon tombac is often used as an alternative for investment cast steel parts, because the mechanical strength is comparable (500

MPa MPA or mPa may refer to: Academia Academic degrees * Master of Performing Arts * Master of Professional Accountancy * Master of Public Administration * Master of Public Affairs Schools * Mesa Preparatory Academy * Morgan Park Academy * Moun ...

), but the production process is more efficient. There can be found a break-even-point when comparing both processes, whereas the advantages of

regularly predominate at high unit numbers (for instance greater than 5000 units) to produce.

' Perspective Mittelstand This alloy has outstanding casting properties and good strength properties,

''Foundry Lexicon which is required for the die casting process. It is often chosen for small to medium size parts in terms of casting metal volume. For large parts often investment casting of steels is applied because of the lower material cost.

Metallurgical aspects

The silicon content limits the solubility of zinc in copper in the α-phase. In the given alloy the maximum amount of silicon at a very high zinc content is added. The consequence is that the α-phase crystallized silicon

supersaturated In physical chemistry, supersaturation occurs with a solution when the concentration of a solute exceeds the concentration specified by the value of solubility at equilibrium. Most commonly the term is applied to a solution of a solid in a ...

when it comes to high cooling rates of the alloy. As a result the α-solid solution does not disintegrate, which leads to the described high mechanical properties.

References

*E. Paul DeGarmo, J. T. Black, Ronald A. Kohser: DeGarmo's Materials and Processes in Manufacturing. 10 Auflage. John Wiley & Sons, 2007, {{ISBN, 978-0470-05512-0 (section: copper-zinc alloys). Copper alloys Silicon alloys Zinc alloys