The main components of zinc alloy are zinc and aluminum. They are both amphoteric metals with poor chemical stability, and are prone to oxidation, discoloration, and corrosion in air
So we must first understand the quality control of the surface condition of electroplated or coated zinc alloy die-casting parts
1.1 Geometric Design of Workpiece
When designing the geometric shape of zinc alloy castings, efforts should be made to avoid structures such as deep blind holes and concave parts. Therefore, it is required to leave drainage holes for solution and gas flow in parts that do not affect appearance and use during part design. This not only enables effective plating, but also reduces the degree of contamination of the plating solution.
1.2 Mold design and die-casting process for die-casting parts
The surface of zinc alloy die-casting parts is a dense layer with a thickness of about 0.1 mm, while the interior is a loose porous structure. When designing molds and using die-casting processes, try to make the surface of the workpiece as smooth as possible, reducing casting defects such as cracks, pores, cold gap, burrs, and burrs. Therefore, mechanical cleaning must be carried out to avoid damaging the surface dense layer and exposing the porous substrate, which may cause difficulties in electroplating and affect the quality of electroplating. Release agents are often used in zinc alloy die-casting, and their use and removal should be given certain attention. They are one of the factors affecting the adhesion of the coating.
1.3 Material selection of workpieces
The commonly used zinc alloy materials for electroplating include 2ZnAl-4-3, 2ZnAl-4-1, 2ZnAl-4-0.5, and 2ZnA14. The most commonly used grades are ZnAl-925 and ZnAl-903, but ZnAl-903 is better than ZnAl-925.
In addition, a portion of the recycled material is commonly used during die casting, and its proportion should be controlled at 15%, preferably not exceeding 20%. Due to the easy doping of other components (such as silicon) in the recycled material, it affects the adhesion of the coating. If using castings with a high amount of recycled materials, it is best to activate them with hydrofluoric acid during electroplating.