Some tips for zinc die casting before plating

Zinc alloy die-casting is a form of processing with high production efficiency in one shot. It can process complex-shaped structural parts and is widely used in furniture hardware, but zinc alloy is not resistant to atmospheric corrosion and must be plated with nickel and chrome protective decorative plating on its exterior. The substrate characteristics of the workpiece itself and the special processing form have a great influence on the plating. An engineer with more than ten years of die-casting experience tells us the following tips.

1) Parts design should be reasonable, the shape of die casting should consider the coverage ability of plating, minimize the non-through hole, or pick the right hanging tool and hanging method in the plating hanging stage so that the water wash does not easily carry the solution. Reduce the sharp corners and other parts, so that the power lines are evenly distributed when plating.

2) The material of alloy die casting is zinc or aluminum alloy, both are active amphoteric metals. And two metals and aluminum in the pretreatment and electroplating in the most difficult to deal with so must control the aluminum content, general rust plating of zinc alloy die casting materials, aluminum content (mass fraction) should not exceed 4%, aluminum content is too high, will make plating difficult to carry out properly.

 

3) Die-casting process, die-casting mold design is reasonable so that die castings do not produce shrinkage, pinholes, loosening, and other defects, in the production of strict testing of the first product to prevent the occurrence of the second class defects produce bad plating, the above defects will directly affect the plating bonding.

4) Copper, nickel, and chrome plating layer is composed of multiple plating species, relative to the substrate is a negative plate plating, only mechanical protection, and zinc alloy parts in the humid air corrosion, so we must ensure that the plating layer without holes. Otherwise, the corrosion products of zinc alloy will make the plating blister. Relative to the steel parts, the plating should be thicker, in order to apply to the zinc alloy die-casting. 

5) Die-casting process, try to reduce the phenomenon of segregation. Such as some parts of aluminum segregation, in the degreasing, aluminum that is the first to dissolve, will produce pores, and pinholes in the die-casting surface and can not be washed, resulting in poor bonding. Resulting in peeling and blistering of the plating.

6) die casting in the die-casting and machining process of the residue, after processing should be cleaned up as much as possible. Because the residue is an active metal, in any process of electroplating, it will react with the solution and destroy the plating solution, resulting in an impact on the quality of the plating. 

7) In the process of grinding and polishing, attention should be paid to the proportion, the dense layer of 0.05~0.1mm formed during the cooling process of die casting surface is very important for plating, and the loss of the dense layer should be minimized when grinding and polishing. 

8) The plating layer of copper, nickel, and chrome, which is composed of multiple plating species, is a negative plating layer relative to the substrate and has only mechanical protection, while the zinc alloy is corroded in the humid air, so the plating layer must be guaranteed to be non-porous. Otherwise, the corrosion products of zinc alloy will make the plating blister. Compared to steel parts, the plating should be thicker in order to be suitable for zinc alloy die castings.