Zinc alloy die-casting parts are now being used around various products. Various electronics and electrical appliances are surrounded by zinc alloy die-casting products. Therefore, the surface quality of the castings is required to be high, and good surface treatment capabilities are required. The most common defect of zinc alloy casting products is surface blistering.
Defect characterization: There are raised vesicles on the surface of the die casting. ① Found after die-casting; ② Revealed after polishing or processing; ③ Appeared after oil spraying or electroplating; ④ Appeared after being placed for a period of time.
Most of the blistering on the surface of zinc alloy is caused by pores, and the pores are mainly pores and shrinkage holes. The pores are often round, and most of the shrinkage holes are irregular.
1. Causes of pores: ① During the filling and solidification process of the molten metal, holes are formed on the surface or inside of the casting due to the intrusion of gas; ② the gas invaded by the volatilization of the coating; ③ the gas content of the alloy liquid is too high and precipitates during solidification.
2. Reasons for shrinkage cavity: ①In the process of molten metal solidification, shrinkage cavity occurs due to the reduction in volume or the final solidified part cannot be fed by the molten metal; ②The uneven thickness of the casting or the partial overheating of the casting causes a certain part Solidification is slow, and cavities are formed on the surface when the volume shrinks.
Due to the existence of pores and shrinkage holes, the holes may enter when the die-casting parts are subjected to surface treatment. When baking after painting and electroplating, the gas in the hole expands by heat; or the water in the hole will turn into steam, which will cause blistering on the surface of the casting.
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Post time: Mar-06-2021