This alloy has a composition very close to the Al-Si eutectic. It therefore has a low melting point (577°C). Aluminium and silicon have no solid solubility below the eutectic and the microstructure solidifies as a silicon particles in an aluminium matrix.

This is an example of an unmodified aluminium-silicon casting alloy, used for sand casting or die casting. The molten metal has high fluidity and solidifies quickly. Aluminium-silicon castings have good corrosion resistance and good weldability. The microstructure can be refined by rapid cooling to increase the strength and ductility.

A similar effect can be achieved through modification which reduces the need for rapid cooling.

Applications include castings for pistons and transmission casings for transport.