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Causes of bubbles in zinc alloy die castings

Essai Industries Co.,Ltd | Updated: Jun 15, 2017

Zinc alloy die castings are widely used in a variety of decorative aspects, such as furniture accessories, building decoration, bathroom accessories, lighting parts, toys, tie clips, belt buckle, all kinds of metal buckle, so on the surface quality of the die castings, at the same time require a good surface treatment performance. The most common flaw in zinc alloy die castings is surface foaming.
Defect characterization: The surface of the die-casting small bubble, die-casting out on the discovery, polishing or processing after exposure, injection or electroplating appeared.
Cause:
Holes caused by: mainly pores and contraction mechanisms, pores are often rounded, and the contraction of most irregular shape.
1. Cause of stomata:
A, metal liquid in the filling, solidification process, because of gas intrusion, resulting in the casting surface or internal holes.
B, paint volatile gas intrusion.
C, the alloy liquid gas content is too high, precipitation during solidification.
When the gas in the cavity, the gas that the coating evaporates, the gas that the alloy solidification precipitates, when the mold row is bad, the blowhole which is formed in the casting is finally left.
2. Causes of shrinkage:
A, metal liquid solidification process, due to the reduction of the volume or the final solidification site can not be filled with metal liquid shrinkage, and the formation of contraction.
b, uneven thickness of the castings or castings local overheating, resulting in a bit of slow solidification, the volume contraction when the surface formed concave position. Due to the existence of pores and shrinkage, so that the casting in the surface treatment, the hole may be water, when the spray painting and electroplating after the time to bake, the hole inside the gas heated expansion or pore water will change steam, volume expansion, resulting in the casting surface foaming.