What Are Internal Combustion Engine Pistons Made Of?by Moss Strohem
The internal combustion piston engine has been used in countless applications from small engines for lawn mowers,to larger engines for aircraft and automobiles, to large diesel engines for trains and ships. The applications and design processes have evolved, and so has the materials they are made from.
The piston is the internal component of the engine that reciprocates up and down in a cylinder, compressing an air/fuel mixture and then exerting force from the controlled explosion of that mixture downward onto the connecting rod and crankshaft.
Pistons are manufactured from alloys of aluminum and silicon. The amount of silicon incorporated into the alloy--which makes the alloy stronger--is dependent on the intended severity of duty of the engine, and also influences the expansion properties of the piston. Stronger alloys with greater silicon content allow smaller size and reduced weight.
Molten aluminum alloy is formed into roughly shaped blanks through either casting or forging, and once piston blanks are created, they are machined to final specification.
Cast pistons are most common due to the simpler and less expensive manufacturing process; molten alloy is poured into a mold of the near-final shape. Once machined, they are suitable for standard performance applications.
These pistons are made from higher strength aluminum alloy billets which are pressed into their basic shape rather than poured. The process results in a piece that has more uniform metallurgical properties that better withstands severe duty.