Electrodeposition Process And Properties Of Ni-P-（Sol） Al₂O₃ Nanocomposite Coating

Nano composite coating has the properties of both matrix metal and nano particles,whichgreatly improves the physical and chemical properties of the matrix itself,and also increases its service life,so it is widely used in aerospace,electronic information,chemical manufacturing and other engineering technologies.With the development of electrodeposition technology and nano manufacturing technology,the types of nano composite plating methods are gradually increasing,and the surface characteristics of the prepared materials are more diverse.The characteristics of nano particles themselves have a great impact on the performance evaluation of the composite coating.On the basis of Ni-P alloy coating,by adding Al₂O₃ particles with high hardness and good wear resistance,using alumina sol to replace the traditional powder,the Ni-P-（Sol）Al₂O₃ nano sol reinforced composite coating was prepared on the surface of Q235 steel by DC and pulse electrodeposition respectively.The results are as follows:（1）On the basis of previous Ni-P plating conditions,adding alumina sol,taking bath temperature,bath pH,alumina sol dosage（concentration ml/L）and current density as four factors,taking deposition rate as index,the optimum process parameters and bath formula of Ni-P-（Sol）Al₂O₃ composite coating under direct current condition were obtained by using four factors and three levels test method.The optimal formula are NiSO₄·6H₂O 120g/L,H₃BO₃ 30 g/L,NaH₂PO₂·H₂O 15 g/L,NiCl₂·6H₂O 20 g/L,Al₂O₃ sol 80mL/L,C₁₂H₂₅SO₄Na 0.4 g/L.The optimum process parameters are 55℃,pH3.5 and current density 7.0A/dm².It is found that the current density is the most important factor affecting the deposition rate.（2）The effect of current density on the properties of Ni-P-（Sol）Al₂O₃ composite coating was studied,the current density ranges from 4 A/dm² to 9 A/dm².The results show that when the current density is 7 A/dm²,the plating speed is 83.92um/h,the hardness is 669.2HV,the wear rate is 1.768×10-6g·m^-1,the wear resistance and corrosion resistance are the best.（3）In order to further optimize the performance of the sol composite coating,the power supply mode was changed from the original DC to one-way square wave pulse,the pulse frequency was fixed at1kHz,and the best value was found within the setting range of duty cycle（10%⁹0%）.The properties of matrix,Ni-P coating,Ni-P-（Sol）Al₂O₃ composite coating under direct current and pulse conditions were characterized by contrast test.The results show that the Ni-P-（Sol）Al₂O₃ composite coating with a duty cycle of 80%has finer,more uniform grains and denser deposition.The highest hardness is 863.4hv and it has good friction and wear properties,and the corrosion resistance of direct-current Ni-P-（Sol）Al₂O₃coating is the best.（4）The rate of nucleation and growth determines the thickness of metal crystal particles.When the nucleation rate is faster than the growth rate of the nucleation,the coating with close crystal arrangement and fine structure can be obtained.There are two types of nucleation:two-dimensional disk model and three-dimensional hemispherical cone model.There are two types of nucleation:two-dimensional growth（2D）and three-dimensional growth（3D）.The models of instantaneous nucleation and continuous nucleation in three-dimensional growth are analyzed.