Passivation and phosphating

Dec -11 -2020

Chromating passivation and phosphating of die casting parts

Chromating passivation and phosphating are very similar surface chemical treatments. Chromate and phosphate are used respectively to remove surface oxidized peel from aluminum or zinc die casting products. The die cast products processed by chromating or phosphating can appear its nature color as a good decoration means. Besides, chromating and phosphating can also be used a primer for powder coating or painting.

Parison die casting is experienced in die casting surface treatments. Lots of aluminum die cast products are required for chromating passivation or phosphating for surface protection or decoration purpose. We are willing to offer more value added service for our customers.

Chromate passivation of die casting products

Chromate conversion coating is applied to passivate aluminum to slow corrosion. The industry is developing less toxic alternatives in order to comply with substance restriction legislation such as Rosh. One alternative is trivalent chromate conversion which is not as effective but less environmentally damaging.

Chromating is commonly used on aluminum casting parts in the aircraft industry where it is often called chemical film. It has additional value as a primer for subsequent organic coatings, as untreated metal, especially aluminium, is difficult to paint or glue. Chromated parts retain their electrical conductivity to varying degrees, depending on coating thickness. The process may be used to add color for decorative or identification purposes.

Phosphating of aluminum die casting products

Phosphating is commonly used for aluminum and zinc die casting surface cleaning and corrosion resistance process. The featured difference from chromate passivation is using phosphate to react with oxidized peel on die casting surface.

Surface corrosion resistance protection: phosphating can remove the oxide peel and make the aluminum or zinc appear its nature color. But after long time exposure in atmosphere, the phosphate surface will be oxidized again, so commonly we will process the die cast work pieces with sealing impregnation.

Primer for further coating: phosphating is an effective fore treatment for painting or powder coating. Commonly we will process 3-4 times of phosphating for aluminum die cast parts before powder coating or painting.

Passivation and phosphating

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