Silumin is a general name for a group of lightweight, high-strength

aluminium alloy An aluminium alloy (or aluminum alloy; see spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two princip ...

s based on an aluminum–silicon system. Aluminium-silicon alloys typically contain 3 to 25%

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 ...

content.

Casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...

is the primary use of aluminum-silicon alloys, but they can also be utilized in rapid solidification processes and

powder metallurgy Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes can reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and r ...

. Alloys used by powder metallurgy, rather than casting, may contain even more silicon, up to 50%. Silumin has a high resistance to

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...

, making it useful in humid environments. The addition of silicon to aluminum also makes it less viscous when in liquid form, which, together with its low cost (as both component elements are relatively cheap to extract), makes it a very good casting alloy. Silumin with good castability may give a stronger finished casting than a potentially stronger alloy that is more difficult to cast. Hypereutectic alloys, with a silicon content of 16 to 19%, such as Alusil, can be used in high-wear applications such as

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas- ...

s, cylinder liners and internal combustion

engine block In an internal combustion engine, the engine block is the structure which contains the cylinders and other components. In an early automotive engine, the engine block consisted of just the cylinder block, to which a separate crankcase was attac ...

s. The metal is etched after casting, exposing hard, wear-resistant silicon precipitates. The rest of the surface becomes slightly porous and retains oil. Overall this makes for an excellent bearing surface, and at lower cost than traditional bronze bearing bushes. Within the Aluminum Association numeric designation system, Silumin corresponds to alloys of two systems: 3xxx, aluminum–silicon alloys also containing magnesium and/or copper, and 4xx.x, binary aluminum–silicon alloys. Copper increases strength, but reduces corrosion resistance.

Characteristics

* High castability, fluidity, corrosion resistance, ductility, and low density. * Usable for large castings, which can operate under heavy load conditions. * Considered to not be a heat-treatable alloy, but the addition of Mg & Cu can allow it to be heat treated, e.g. AΠ4 alloys. * Strengthened by solution treatment, e.g. adding 0.01% sodium (in the form of

sodium fluoride Sodium fluoride (NaF) is an inorganic compound with the formula . It is used in trace amounts in the fluoridation of drinking water, in toothpaste, in metallurgy, and as a flux. It is a colorless or white solid that is readily soluble in water. ...

aFand

sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35 ...

aCl to the melt just before casting. * A disadvantage is a tendency for porosity in the casting, i.e. the casting can become foam-like. This can be avoided by casting under pressure in

autoclave An autoclave is a machine used to carry out industrial and scientific processes requiring elevated temperature and pressure in relation to ambient pressure and/or temperature. Autoclaves are used before surgical procedures to perform steriliza ...

References

Aluminium alloys Aluminium–silicon alloys {{Alloy-stub