Okay - here's a quick lesson in metallurgy - a eutectic reaction is a phase
transformation whereby a liquid metal (single phase) cools though a certain
temperature (the eutectic temperature), and transforms into two distinct
solid phases. This reaction can be graphically expressed on a binary phase
diagram. In the case of cast aluminum pistons, we would be talking about the
Aluminum-Silicon phase diagram. There is only one very specific composition
at which the eutectic reaction occurs. Compositions which contain less
Silicon and more Aluminum than this eutectic composition are said to be
Hypoeutectic. Compositions which have a higher Silicon content, and
correspondingly less Aluminum than the eutectic composition are said to be
Hypereutectic.
In the case of cast pistons, it just so happens that pistons cast from
Hypereutectic compositions display mechanical and physical properties which
make them more attractive for use as high-performance parts.
SteveM.
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 11:48:45 EDT