Question

What method of heat treatment is used for pistons in 4-stroke engines. What chemicals are used in the process and why.

Answer 1

Piston material of a 4 stroke engine is usually made of Al-Si-Ni-Mg-Fe alloys. This should have high mechanical strength at elevated temperature.

The most common methods of heat treatment applied
to piston alloys are solution heat treatment, aging and
stabilization. The solution heat treatment
comprises heating the piston materials to the maximum
allowable temperature, which is very close to the eutectic
melting temperature, the period of holding them at this
temperature and the cooling rate. The heating tempera-
ture depends on the nature of an alloy and is based on the
equilibrium phase diagram. The duration
of the holding time has a significant influence on the
wall thickness and configuration as well as on the casting
process. Aging is often the final operation
of heat treatment.

Solution treatment is the heating of an alloy to a suitable temperature, holding it at that temperature long enough and then cooling it rapidly enough to hold these constituents in solid solution.

Material is dipped in heat treatments salts like pottasim nitrate and sodium nitrate salts. This helps to remove scales.