| Ni-Co-P plating as a protective and decorative coating,Its hardness and corrosion resistance are significantly better than those of Ni-Co and Ni-P coatings,which shows a good application prospects in industry.In this paper,the plating process of Ni-Co-P plating is studied with the hardness and gloss of the plated layer as the evaluation index,and the effect of heat treatment on the performance of the plated layer is also studied.The paper firstly screened the composition of the base plating solution and plating process parameters for Ni-Co-P plating by single-factor experiment,and determined the best base plating solution composition for Ni-Co-P plating:nickel sulfate of 200 g/L,cobalt sulfate of 15 g/L,sodium hypophosphite of 10 g/L,sodium citrate of 80 g/L;the plating process parameters were:current density of 2.5 A·dm-2,temperature of 60℃,pH 4.5,the plated layers were plated for 50 min under these conditions and analyzed by SEM,electrochemical workstation and microhardness tester.The results showed that the surface of the Ni-Co-P plating was smooth and flat,and the hardness was much higher than that of Ni-P and Ni-Co alloy plating;the corrosion resistance of Ni-Co-P plating was slightly lower than that of Ni-P alloy plating,and it was significantly better than that of Ni-Co alloy plating;the hardness of Ni-Co-P plating was 385.06 HV0.5,the gloss was 367 GU,the corrosion potential was-0.452 V,corrosion current was 5.44×10-8A·cm-2;the content of each component in the plating was 68.03 At%Ni,23.48 At%Co and 8.13 At%P.The best basic process for electroplating Ni-Co-P coatings,adding additives to the plating solution,designing response surface experiments to screen and compound the additives,and obtaining the formula of the additive combination that makes the coating hard and glossy:SDS concentration of 0.10 g/L,thiourea concentration of0.15 g/L,and sodium allyl sulfonate concentration of 0.22 g/L.The Ni-Co-P coating was produced under this additive formulation,and the coating performance test results showed that the coating surface was smooth and flat,with dense structure and no pinpoint pockmarks,and the hardness and gloss of the coating increased significantly to 475.4 HV0.5and 463.4 GU,respectively,and the corrosion resistance of the coating was enhanced,and the content of each component in the coating was71.01 At%Ni,20.65 At%Co,8.34 At%P.The Ni-Co-P coating was produced in the plating solution with compound additives,and the performance of the coating was tested after heat treatment.The results show that the heat treatment affects the structure of Ni-Co-P coating,which gradually transforms the coating from amorphous state to crystalline state;when the heat treatment temperature is 400℃,the surface of the coating is flat and dense without defects,and the hardness of the coating is the highest and the corrosion resistance is the best. |
