سبيكة فائقة الانصهار

السبيكة فائقة الانصهار Hypereutectic alloys، are alloys which have less eutectic mixture than minor alloying element.

Cast pistons are made from aluminium.

"These alloys have good mechanical properties at high temperatures and are very castable" according to David Weiss

hhand Silicon which forms alloy. General behaviour of alloy is based on this basic compositiom but ther are also other elements added.

Silicon improves machinability and fiminish the hardness of aluminium. Lowest melting point mixture of series and also eutectic has big amount of Silicon approximately 13.0.

Eutectic aluminium alloys melt at degree lower than pure aluminium of the higher strength alloys (it is about 498 degC). Other main advantage of aluminium silicon ally with a eutectic composition is that it has a relatively low expanstion rate and so tolerances can be maintaned and piston slap can be avoided when the engine is cold.

Eutectic alloys are good for die casting and solidifity at a fixed temperature.

The other bonus of eutectic composition of aluminium silicon alloy is that it has a low expansion rate and so piston slap can be avoided and tolerances can be maintained when the engine is cold.

Hypereutectic pistons expand less than eutectipc pistons.

Hypereutectic pistons tend to contain approximately 17 silicon and there is a bit free silicon present.

Alloys melt at around 550 degC and they are not as good as forged pistons but are better than eutectic pistons.

The Cast pistons are generally stronger and more ductile than competition forged pistons.Competition forged pistons need careful warm up as they expand quite substantially and they have better high temperature characteristics.

Some forged pistons have about 15 % silicon conent(Mb?,Bmw) and still avoid piston slap

"Piston slap is defined as the rocking of the piston in the cylinder. This means that it is not moving up and down the cylinder as it desires it is being forced to" -Tom Harbid

whilst cold but the forging process breaks up the cast structure. Moreover, they tend to make better resistance and melt in high performance engines.

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