Silicon tombac () is an

alloy An alloy is a mixture of chemical elements of which in most cases at least one is a metal, metallic element, although it is also sometimes used for mixtures of elements; herein only metallic alloys are described. Metallic alloys often have prop ...

made of

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

(80%),

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It 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 tabl ...

(16%) and

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

(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 and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. I ...

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

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

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 process, which is normally specialized on

metals A metal () is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. These properties are all associated with having electrons available at the Fermi level, as against no ...

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 * M ...

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