TENDENECY OF MATERIAL :-

Like galvanized sheets, die casting material has tendency to undergo natural corrosion forming a thin layer of zinc oxide or zinc carbonate on the surface which we commonly call as white rust. This material is porous, hence must be properly dried after pretreatment.

NEED OF CLEANING -

PRESENCE OF OIL AND/OR LAYER OF WHITE RUST ON IT’S SURFACE

NEED OF CONVERSION COATING :-

TO PREVENT FURTHER OXIDATION OF CLEANED SURFACE OF DIECASTING MATERIAL

PRECLEANING OF DIE CASTING MATERIAL

Mild alkaline cleaners
Like aluminium, this material is very sensitive to alkaline attack. There for alkaline cleaners are milder for this material. Strong alkaline cleaners are not used because they over etch the material leaving black smut which can not be removed even in nitric acid completely. This also leaves powdery layer on the material which is not good for the bonding of powder coating.

Acidic Cleaning
These are based on phosphoric acid. They are capable of removing white rust along with oil without formation of black smut if proper timing is given.

CONVERSION COATING FOR DIE CASTING MATERIAL

Chromate coating – Golden Yellow in colour