Cast pig iron parts, the surface is often uneven and porous, on such a surface will only get a rough and porous coating. In addition, on the surface of the pig iron, there is free graphite, it not only affects the combination of the coating and the matrix metal, at the same time, in the case of pores in the coating, it becomes the cathode of the corrosion battery, so that the coating metal is rapidly destroyed, the graphite in the pig iron, sometimes also has the effect of reducing hydrogen overvoltage, resulting in hydrogen easy to precipitate there, hindering the deposition of metal, so, Cast pig iron parts are more difficult to electroplate than other steel parts.