Silumin is a general name for a group of lightweight, high-strength aluminium alloys based on an aluminum–silicon system. Aluminium-silicon alloys typically contain 3 to 25% siliconcontent. Casting is the primary use of aluminum-silicon alloys, but they can also be utilized in rapid solidification processes and powder metallurgy. Alloys used by powder metallurgy, rather than casting, may contain even more silicon, up to 50%. Silumin has a high resistance to corrosion, 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, 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 pistons, cylinder liners and internal combustion engineblocks. 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 reducescorrosion 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 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 autoclaves.
