Zinc Alloy Die Casting Influencing Electroplating
Die casting is once shaping processing having high production efficiency. Die casting can process structural components which have complex shapes, having widely applied in automobile and bathroom products. However, zinc alloy has low atmosphere corrosion resistance. For this, the surface should be covered with decorative protection plating such as copper and chrome. The properties of zinc alloy die casting and particular processing types have great influences on electroplating.
1. The raw material of die casting is zinc aluminum alloy. Both zinc and aluminum are active amphoteric metals. For the two metals, pretreatment and electroplating on aluminum are the most difficult. So, the aluminum content must be contained. In general, for electroplated zinc alloy die casting, the aluminum content cannot exceed 4%. If the aluminum content is too high, it is difficult to carry out electroplating.
2. The design of components should be rational. The shape of die casting should be based on covering power of electroplating. Dead holes should be reduced as much as possible so that washing cannot take solution easily. Reduce sharp corners and other parts, making power lines distribution homogeneous.
3. Die casting technique and design of die casting also should be rational so that die casting cannot produce shrinkage cavity, pinholes or porosity. Those defects have direct influence on binding force of plating.
4. Segregation should be decreased as much as possible during die casting, like aluminum segregation on some parts. During degreasing, aluminum is the first to dissolve. Pores or pinholes are formed on the surface of die casting which cannot be cleaned up, causing poor binding force and resulting plating dehulling or blistering.
5. Polishing needs consideration. 0.05~0.1mm compact layer formed on the surface of die casting during cooling is vital for electroplating. During polishing, the compact layer should be lost as less as possible. If the layer is polished, the porous structure is exposed and good electroplated layer cannot be acquired on the layer.
6. Copper-nickel-chrome electroplated layer which consists of various metals is cathode plating in terms of matrix, only having mechanical protection. But, zinc alloy is corroded in humid air. So, the holes are not allowed to exist on plating. Otherwise, corrosion products on zinc alloy make plating blister. For steel, the plating should be thicker, only suitable of zinc alloy die casting.
7. Residuals on die casting formed during processing must be cleaned up after processing. Because residuals are also active metals which can react with solution in any procedures of electroplating, destructing solution and impacting quality of electroplating.