Analysis of Causes of Foaming in Zinc Alloy Die Castings

Zinc alloy die castings are currently widely used in many industries, such as furniture accessories, architectural decoration, electronic digital accessories, bathroom accessories, lighting parts, luggage accessories, various metal buckles, etc. The surface treatment process is also very extensive, including electroplating ( Water plating), oil spraying, powder spraying, vacuum plating, baking varnish, electrophoresis, passivation and so on. Different surface treatment processes have different requirements for the surface quality of castings, and at the same time require good surface treatment performance. The most common defect of zinc alloy die castings is surface blistering.


Surface blistering characteristics: blistering on the surface of the die casting blank, blistering after polishing or processing of the die casting, blistering after the surface treatment of the die casting or electroplating. cause:


1: The surface of the die-casting blank is blistered, a. It is too early to eject the casting when the mold is opened; b. The mold temperature is too high during ejection; c. The mold runner design is unreasonable, resulting in poor water flow. Because there are a large number of bubbles inside the die casting, when the metal solidification time is not enough, the strength is not established, and the casting is ejected prematurely, the pressure bubbles expand and the surface of the casting is raised and hot cracks are generated. Commonly used solutions: adjust the process parameters of the die-casting process to keep the mold longer; reduce the mold temperature in the defect area; improve the design of the mold feed runner.


2: Die-casting parts blistering after polishing or processing, a. Before mechanical polishing, the quality of die-casting must be inspected first. Because improper mold design and casting technology can cause defects in the surface layer, such as crevices, subcutaneous blistering, pores, cracks, etc., which are potential sources of corrosion and one of the main factors affecting the quality of the coating, and the die-casting quality is unqualified , Do not enter the polishing process. The surface is required to be smooth, dense, and smooth, without cold lines, and no pores. In terms of zinc alloy polishing, the main thing is to pass the hemp wheel first, and then use the cloth wheel (if the nozzle is not large or you do not want to lose too much of the object, you can directly use the cloth wheel).


3: Foaming after surface treatment of die casting, a. Pre-treatment process and processing process problems, here is the most common electroplating process as an example, the common process flow is as follows: pre-treatment→cleaning→alkaline copper plating→cleaning→pyrophosphate plating Copper→cleaning→acid copper plating→cleaning→semi-gloss nickel→full-gloss nickel→cleaning→chrome plating→drying. The pre-treatment and processing methods of different surface treatments are different, and they should be processed in accordance with the standard operating procedures of the surface treatment process of die castings. In addition, poor polishing is also an important cause of blistering after surface treatment.


In addition to the zinc alloy die castings, aluminum alloy die castings and magnesium alloy die castings all have surface blistering, and their characteristics are roughly similar to those of zinc alloy die castings. The surface blistering of die castings needs to find the exact cause for targeted improvement. Combining the knowledge and understanding of die-casting basic knowledge of various die-casting manufacturers, so as to better solve various defects of die-casting parts and improve product quality.

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