Plating on Zinc Die Casting
Zinc die castings are a unique choice for countless decorative and functional applications. Zinc is a relatively dense metal, which has a feel of “substance” and durability. Zinc casting alloys are also stronger than all but the most highly reinforced molded polymers. Zinc’s hardness, self lubricating properties, and dimensional stability make it suitable for working mechanical parts, such as gears and pinions that would be less durable if molded from polymers.
Zinc can be die cast at moderate temperatures thus providing significant energy and processing savings over other metals and engineering alloys. Zinc also accepts a broad assortment of finishes, from chemical conversion treatments to electroplating to sprayed and baked polymers.
Nickel chrome plating has been used on zinc die casting for many years going back to the classic car plating of the 1940’s through the 1960’s.
This process is common for Exterior automotive trim including:
- Headlight casings
- Hood ornaments
- Window and panel trim
- Interior door handles
- Instrument bezels and buttons
On zinc it begins with a thin layer of cyanide (non-acid) copper flash to protect the zinc against the acidity of subsequent baths. The next step includes a layer of acid copper plate, which serves to make the surface more uniform and assures good electrical conductivity. This is followed with one or more layers of nickel, which provides a continuous corrosion resistant barrier. Finally chromium is applied to give the desired shiny “silvery” appearance and to protect the nickel against mechanical forces such as wear and erosion.
To obtain the best finish on zinc die castings, a “copper buff” step needs to be done. After the initial polish and buff, the zinc die casting is electroplated with a heavy deposit of copper. After copper plating, the parts are then buffed again to further smooth out the surface. The final step is to activate the copper surface and electroplate with nickel and chromium.