Aluminum alloy die casting is a highly efficient form of processing in a single pass. It can process structural parts with complex shapes and is widely used in automobiles and home bathrooms, but zinc alloy is not resistant to atmospheric corrosion and must be plated with copper and chromium to protect the decorative coating on its surface. The workpiece itself matrix properties and special processing form has a great influence on the plating.
(1) alloy die-casting material for zinc-aluminum alloy, is active amphoteric metal. Among these two metals, aluminum is the most difficult to deal with in pretreatment and plating, so the content of aluminum must be controlled. The aluminum content (mass fraction) of zinc alloy die-casting materials for general antirust plating is not more than 4%, and the aluminum content is not more than 4%. If it is too high, plating will be difficult to proceed normally.
(2) the design of the parts should be reasonable, the shape of the die casting should consider the plating coverage ability, minimize the non-through hole, so that the water washing is not easy to carry solution . Reduce the sharp corners and other parts, so that the plating power line distribution is uniform.
(3) die-casting process and die-casting mold design is reasonable, so that the die casting does not produce shrinkage holes, pinholes and air holes and other defects, which directly affects the combination of plating.
(4) in the die-casting process, should minimize the phenomenon of segregation. If some parts of aluminum segregation, degreasing aluminum first dissolved, so that the die casting surface produces air holes and pinholes, can not clean up, resulting in poor adhesion. Resulting in coating spalling and blistering.
(5) In the grinding and polishing process, pay attention to the size. The dense layer of 0.05-0.1mm formed during the cooling process on the surface of the die casting is very important for electroplating. During grinding and polishing, the loss of the dense layer should be minimized. If this layer is ground off, you will expose a porous structure and you will not get a good plating on this layer.
(6) Multiple plating compositions of copper-nickel-chromium plating is a cathodic plating relative to the substrate, and has only a mechanical protective effect, while zinc alloy parts will corrode in moist air, so it is important to ensure that the plating does not corrode. Porous. . Otherwise the corrosion products of the zinc alloy will cause the coating to blister. Compared with steel parts, the coating should be thicker for zinc alloy die castings.
(7) Die casting and machining process generated during the die casting residue, after processing should be cleaned up as much as possible. As the residue is an active metal, it will react with the solution and destroy the plating solution in any plating process, thus affecting the plating quality.