Solutions to Blisters on Surfaces of Die Casts

1. Reduce the air content in the die cast.
The key to controlling the forming of the blister is to reduce the amount of gas getting into the die cast.

2. Avoid Shrinkage cavities.
During the solidification process, every part of the die cast should have uniform heat dissipation and solidification at the same time. Reasonable gate designs, thickness and positions of ingate, mold designs, mold temperature control and cooling can help avoid shrinkage cavities. 

3. Reduce water lines, cold shuts and hot cracks.
Improving the mold temperature, increasing the flow gate speed or enlarging overflow launders in the cold shut areas can reduce occurrences of cold shuts.

Die casting thickness shouldn't change sharply so that the stress can be reduced. The related parameters of die casting processes should be adjusted; the mold temperature and the material temperature should be reduced.

4. Primarily control the content of the harmful impurity in the alloy material to prevent intergranular corrosion. 

5. Carefully check the molds and die casting products; optimize plans of molds and die casting products.

6. The adhesion size of burnishing is from 0.045 to 0.069.
Tumbling should be done with granite ceramics, tumbling liquids, cleaning agents and wax solvents. Different die casting products require different specifications of granite ceramics. The ratio of rolling stones and die casting product is 2.5:1.0. The roller speed shouldn't be too high and the time should be from 1.5 to 2.0 hours. Different die casting products have different polishing requirements; usually, die casting products are roughly polished by cloth wheels and then they are carefully polished. The peripheral speed of the cloth wheel can't be too high. Small die casting products should have relatively low speeds, so that hardened layers of die casting products' surfaces can't be damaged. After fine polishing, die casting products should be  placed with white powders, separated by soft objects as well as electroplated timely.

7. Clean die casting products before polishing.
Generally, we use organic solvents, surfactants or cooling liquid for preliminary cleaning of die casting products. Alkaline chemical solvents and electrocleaning are mainly used to degrease zinc alloy die casting parts. After the degreasing process, the die cast should be etched and activated so as to improve the adhesive force of post electroplating processes. However, we need to make sure of purity and concentration of solutions and cleanliness of tanks. Thoroughly clean cleaning tanks and etch and activation tanks, which is the most important and the key to having the effect of electroplating.

8. After polishing, degreasing and cleaning processes, the die casting product should be electroplated completely within 12 hours. Electroplated die casting products should be packed and placed in dry and ventilated areas as well as not be exposed to the sun.