Views:43 Author:Site Editor Publish Time: 2021-05-05 Origin:Site
Zinc die casting parts have low material cost, and with die-casting, one-step forming can produce parts with small tolerances and complex shapes, with high production efficiency and low processing costs. At the same time, zinc is widely distributed in nature and has large reserves. Therefore, it is widely used in industry. Zinc alloy die-casting parts, especially structural parts and decorative parts made of copper, copper alloy and steel materials that are not stressed and have more complex shapes, are widely used zinc alloy die-casting parts.
Due to the poor chemical stability of zinc alloys, copper-nickel-chromium multilayer protective decorative coatings are required. In order to improve the pass rate of electroplated products, zinc alloy materials with an aluminum content of about 4% are generally selected. When electroplating zinc alloy die castings, pay attention to the following characteristics of zinc alloy die castings, and take appropriate measures to improve the qualification rate of electroplated products.
(1) The surface of the zinc alloy die casting part is a dense surface layer, and the thickness of the dense layer is only 0.05 to 0.1 mm. Below the surface layer is a loose and porous structure. For this reason, when polishing and polishing, do not throw all the surface away and expose the loose bottom layer. Otherwise, electroplating is very difficult, the qualified rate of electroplated products is low, and the corrosion resistance will be reduced.
(2) Zinc alloy die castings change from a molten state to a solid state during the die casting process. Because of the different freezing points during cooling, segregation tends to occur on the surface of the die-casting parts, causing some parts of the surface to produce aluminum-rich phases or zinc-rich phases. Zinc and aluminum are amphoteric metals, which are soluble in both acid and alkali. Therefore, strong alkalis should not be used for degreasing and strong acid etching during pre-plating. Strong alkali can dissolve the aluminum-rich phase first, and strong acid can dissolve the zinc-rich phase first, thereby producing pinholes and micro-pores on the surface of the die-casting part, and leaving lye or acid in the holes, causing coating drums during electroplating. Defects such as blistering, peeling or incomplete coating. For this reason, zinc alloy die castings can only choose weak alkali degreasing and low-concentration acid etching, and the temperature should not be too high and the time should not be too long.
(3) The shape of zinc alloy die castings is generally more complicated. In order to avoid incomplete plating and incomplete coating, to prevent the replacement of metal ions with positive potential in deep recesses or shelters, zinc and aluminum will form loose, rough, and bonded For poor replacement plating, a plating solution with better coverage and dispersion capability should be used during electroplating. This is especially important for the plating. Generally, a pre-plating copper solution with high free cyanide and low copper content is used, and an impulse current is also used. To ensure that the deep recesses and shelters can be plated with copper.
(4) The selected coating is best to be a bright coating, try to avoid the polishing process or reduce the polishing workload, on the one hand, it is not easy to polish due to the complicated shape, and on the other hand, the thickness of the coating can be guaranteed to ensure the quality.