Treatment Technology for The Surface of Aluminum Alloy Pressure Die Casting Parts

2020.03.30

Since magnesium alloys are extremely active and often have a layer of oxide on the surface, the surface treatment of magnesium alloy pressure die casting parts is somewhat difficult. Special treatment methods must be used. Existing surface treatment techniques are immature, often making the alloy surface rough and using a large amount of non-environmental chemicals. In recent years, there have been new developments in advanced surface treatment technologies for magnesium alloy pressure die casting parts.

The developed technology includes electroplating, conversion layers, and anodization.

1. Electroplating
Magnesium alloy electroplating is mainly divided into two types. One is to directly carry out electroless nickel after activation of the alloy; on the other hand, it can be electroplated after being zinc-plated. The relevant process is as follows:

Direct electroless nickel deposition

Degreasing→Acid Washing→Activation 1→Activation 2→Electroless Nickel→Heat Treatment→Electroplating Copper→Other Plating

Zinc precipitation method

Degreasing→Acid Washing→Activation 1→Activation 2→Zinc Precipitation→Electroplating Copper→Other Plating

2. Anodizing
The biggest advantage of magnesium alloy anodized film is that it is hard, wear resistant, corrosion resistant, and insulated. The process is as follows:

Degreasing→Acid Washing→Anodizing→Dyeing

Through special equipment and electrolyte, select the appropriate voltage, generate plasma and micro-arc in the oxidation process, which will form a dense and hard ceramic oxide layer on the surface of the magnesium alloy, and pass >100 Hour salt spray test. The surface of the treated magnesium alloy can be dyed by reference to general aluminum anodization, or directly coated with an organic coating or other kinds of coatings.

3. Conversion Layer
In terms of conversion layer, chrome is the most common method, and the effect is also the best; however, due to environmental issues, the use of hexavalent chromium (Cr6+) technology is a must. Therefore, the intrinsic chromizing is replaced by phosphating, and certain achievements have been made. The phosphatized magnesium alloy can pass the 24-hour neutral salt spray test. After the surface is coated with the organic coating, the salt spray test can even exceed 300 hours. The phosphating layer can also enhance the adhesion of magnesium alloy and paint.