Basic Research On The Application Of Crack-Free Hard Chromium Electroplating

Chromium plating layer is widely used in mechanical components because of its excellent wear resistance,color and high hardness.However,the traditional electroplated chromium layer has the penetrating crack,which looks like network that seriously affects the corrosion resistance and wear resistance of the parts.At the same time,due to the poor dispersion of the plating solution,the thickness of the coating is uneven,which increases the difficulty of the subsequent process.So the application of chromium plating is limited.In order to solve the above issues,the basic application of crack-free pulse plating hard chromium was studied,which was based on the free particle polishing-assisted process.The following work has been done:1.Experimental research of crack-free chromium electroplating based on the free particle polishing-assisted crack-free hard chromium plating process was carried out on the 300 M steel substrate.Influences of coating thickness and process parameters on microstructure,hardness,fatigued strength and wear resistance have been studied,analyzed and summarized.The results were following: chromium layer prepared by free particle polishing-assisted hard chromium plating had dense microstructure and no crack on the surface.Under certain process parameters,the hardness of chromium plating layer was between 750 HV to 850 HV,much higher than traditional hard chromium plating layer.Meanwhile,the wear resistance,shear strength and bending fatigue performance of the chromium plating layer were improved.The wear resistance increased with the increase of coating thickness,the decrease of current density,the decrease of cathode speed and the increase of pulse frequency.2.The COMSOL software has been used to simulate the auxiliary cathode,the insulation shield and the anode-cathode distance in order to improve the uniformity of the thickness of the chromium plating layer.The results showed that the thickness uniformity of chromium plating layer could be improved by using appropriate polar distance,auxiliary cathode with the same diameter of cathode and increasing the height of auxiliary cathode.3.The corresponding fixtures including the rotary sealing structure and electric structure have been designed based on different characteristics of revolving parts and the simulation results.The hard chromium plating experiments were carried by the suitable parameters on the basis of the rules obtained from the basic experiment.