Aluminium–silicon alloys

Important areas of application are in car parts, including engine blocks and pistons.

In addition, their use as a functional material for high-energy heat storage in electric vehicles is currently being focused on.

[1] Casting is the primary use of aluminum-silicon alloys, but they can also be utilized in rapid solidification processes and powder metallurgy.

Additions of about 1% Cu are alloyed to increase strength through solid solution strengthening.

[3] Silicon powders are used in aluminum-silicon alloys for enhancing strength and castability, providing better durability under high-stress conditions.

[4] It also improves the fluidity of molten aluminum which allows easier casting of complex shapes with fewer defects.

The pure AlSi alloys are medium strength, non-hardenable, but corrosion resistant, even in salt water environments.

Otherwise, AlSi alloys generally have favorable casting properties: the shrinkage is only 1.25% and the influence of the wall thickness is small.

[10] 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 engine blocks.

The microstructure is consequently characterized by primary aluminium, which is often present in the form of dendrites, and the eutectic of the residual melt lying between them.

[7][12] In sand casting in particular, with its slow cooling rates, additional elements are added to the melt to prevent degeneration.

Above all, the flowability and mold filling ability is very good, which is why eutectic alloys are suitable for thin-walled parts.

[17] AlSiMg alloys with small additions of magnesium (below 0.3 to 0.6% Mg) can be hardened both cold and warm.

They are related to the AlMgSi alloys: Both are based on the fact that magnesium silicide Mg2Si is precipitated, which is present in the material in the form of finely divided particles and thus increases the strength.

However, copper is present as an impurity in some AlSiMg alloys, which reduces corrosion resistance.

[18][19] AlSiCu alloys are also heat-hardenable and additionally high-strength, but susceptible to corrosion and less, but still adequately, castable.

An example use-case are wheel rims produced by low -pressure casting because of their good strength, corrosion resistance and elongation at break.

Alloys with about 10% Si are used for cylinder heads, switch housings, intake manifolds, transformer tanks, wheel suspensions and oil pans.

[27] The copper-containing AlSiCu alloys are used for gear housings, crankcases and cylinder heads because of their heat resistance and hardenability.

[28] In addition to the use of AlSi alloys as a structural material, in which the mechanical properties are paramount, another area of application is latent heat storage.

In the phase change of the alloy at 577 °C, thermal energy can be stored in the form of the enthalpy of fusion.

These advantageous properties of mPCM such as AlSi are of particular importance for vehicle applications, since low masses and volumes as well as high thermal performance are the main goals here.

Hot-dip aluminized sheet steel is an inexpensive material for thermally stressed components.