The surface of cast pig iron parts is often uneven and porous, and only rough and porous coating can be obtained on such surface. In addition, there are free graphite on the surface of pig iron, which not only affects the bonding between the coating and the base metal, but also becomes the cathode of the corrosion battery when there are pores in the coating, which makes the coating metal quickly destroyed. Sometimes, the graphite in pig iron can reduce the hydrogen overvoltage, which makes hydrogen easy to precipitate at this place and hinders the metal deposition, Therefore, it is difficult to electroplate cast pig iron parts than other steel parts.