PLATING SOLUTION AND PLATING PROCESS FOR MULTI-LAYER CYANIDE-FREE PLATING COPPER-TIN ALLOY COATING, AND COINS MADE BY THE PROCESS

摘要

The present invention relates to the technical field of coinage, and particularly to a plating solution and a plating process for a multi-layer cyanide-free plating copper-tin alloy coating, and coins made by the process. The pyrophosphate plating solution for a multilayer cyanide-free plating copper-tin alloy coating of the present invention comprises a cyanide-free main brightener based on tin-brass consisting of brighteners A and B, and the concentration of the brightener A in the main brightener is 1-10 g/L; the concentration of the brightener B in the main brightener is 0.05-0.5 g/L. With this pyrophosphate plating solution and the plating process for a multi-layer cyanide-free plating copper-tin alloy coating, the thickness of the coating of more than 20 µm can be achieved, and coin products with a dense and uniform coating can be obtained. A coating on a coin formed after high-temperature heat treatment has a single-layer structure, the content of tin in the single-layer coating by weight is 11% to 14%; the appearance of the coating is even and golden without chromatic aberration. Therefore, the well-recognized difficult problem in the plating industry that a single-layer cyanide-free plating alloy coating is thin is solved.