When using alkaline zinc nickel alloy additives on cast iron workpieces, due to their special processing, complex structure, and easy rusting of the cast iron surface, it is difficult to treat after rusting, resulting in poor decorative properties. Therefore, it is necessary to improve their surface properties during the electroplating process. Regarding the particularity of cast iron, attention should be paid to these three points during electroplating:
1.A non-conductive oxide film will form on the surface of cast iron during high-temperature casting, which will hinder the deposition of zinc nickel alloy coating. Therefore, the oxide scale on the surface of the workpiece should be thoroughly removed before electroplating. Bigley suggests using shot blasting mechanical polishing on the surface, which can not only effectively remove the oxide scale, but also cause the high carbon layer formed during casting to peel off, resulting in micro roughness and improving the adhesion of the coating.
2.The structure of cast iron substrate is loose and porous, with a large number of sand holes, loose and uneven surfaces. Therefore, the surface area will be much larger than the macroscopic area, resulting in a much lower actual current density than the displayed current density. Therefore, in the process of electroplating zinc nickel alloy, the current density should be 1-2 times higher than other steel substrates. Only by instantly activating the surface through the impact of high current can the loose surface be covered by a dense coating.
3.Acid washing and ultrasonic cleaning processes should be strengthened. Due to the presence of large amounts of grease, lubricating oil, and coolant during the processing of cast iron parts, as well as insoluble pollutants such as oxide films generated by sand particles and iron filings from mold residues during storage, and the fact that cast iron parts themselves contain a large amount of graphite, pre-treatment processes such as acid washing and ultrasonic cleaning should be strengthened during zinc nickel alloy electroplating to form a uniform, clean, conductive, and easily electroplated zinc nickel alloy coating.
In this way, the treatment of cast iron parts through the above three points can improve their surface properties and better utilize alkaline zinc nickel alloy additives. If you are interested in alkaline zinc nickel alloy additives, please contact Bigely customer service for free samples and detailed technical information!
