Effect of process factors on sulfamate plating and optimization
Aiming at the problem that the tensile strength of nickel-cobalt coating cannot meet the indus-trial demand,in order to improve the electroplating process of sulfamate plating solution,the orthogo-nal test was designed by using electrochemical workstation,electronic universal testing machine,microhardness tester,XRD,SEM and other test methods.The effects of temperature,main salt concen-tration and current density on the polarization curve of electroplating reaction,electrochemical kinetic parameters,tensile strength,hardness,crystal structure and surface morphology of electroplating layer were studied.The optimal experimental scheme was obtained by orthogonal and single factor analysis of tensile strength.The results show that the nickel salt concentration has a significant positive effect on the electrode exchange current density j0,and corresponding j0 range is 0.002 mA/dm2‒1.640 mA/dm2;the concentration of cobalt salt has a negative effect on the side reaction of hydrogen evolution,which can reduce the hydrogen evolution efficiency to 0.3%.The influence degree of processfactors on tensile strength and hardness is as follows:temperature>cobalt salt concentration>current density>nickel salt concentration and temperature>current density>cobalt salt concentration>nickel salt concentra-tion.The optimization results are as follows:nickel sulfamate 400 g/L,cobalt sulfamate 30 g/L,tem-perature 50 ℃,current density 3 A/dm2,tensile strength 853 MPa,Vickers hardness 234 HV;the tem-perature has a significant effect on the performance of the sulfamate electroplating system and the quali-ty of the coating.When the temperature increases,the grain of the nickel-cobalt coating changes from(200)preferred orientation to(111)and(220)growth.
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