Study On Process And Properties Of Brush Electro-Plating Ni-P Alloy On Stainless Steel

This paper based on the304stainless steel for research object focus on the study of theactivation process and nickel preplating process in the stainless steel brush electro-platingpretreatment. It was found that2#activation fluid used in combination with1#activationfluid makes the best bonding force; with adoption of special nickel as a preplated layer, themoderate thickness is beneficial to the improvement of the bonding force between theplating layer and the substrate. Moreover, an orthogonal experiment was adopted tooptimize the brush plating pretreatment by using the bonding force as target, and thedetermined optimum process of the pretreatment comprises the following conditions:positive electro-cleaning of an electro-cleaning fluid with the voltage of12V, time of30seconds and relative motion velocity of8m/min（12V/30s/8m/min）; negative activation ofthe2#activation fluid with the technical parameters of12V/20s/20m/min; negativeactivation of the1#activation fluid with the technical parameters of12V/20s/14m/min;positive activation of the1#activation fluid with the technical parameters of12V/15s/14m/min and special nickel preplating with technical parameters of12V/60s/14m/min.The plated layer of quick nickel was brush-plated by using the optimized stainless steelpretreatment process; after78times of thermal shock experiments, the plated layer did notfall off or peel.This paper was also based on the process of brush electro-plating Ni-P alloy on the304stainless steel for research object. A single factor experiment was adopted in studying theinfluences on the quality of the plated layer of the concentration of each component in theNi-P alloy brush electro-plating solution and the technical conditions, by using thedepositing speed and the phosphorus content of the plated layer as target. The resultsindicated that the depositing speed and the P content of the plated layer can be improved byincreasing the concentration of nickel sulfate, concentration of sodium hypophosphite, PHvalue or working voltage, but both the depositing speed and the phosphorus content of theplated layer are reduced when the parameters exceed a certain limit; meanwhile, thedepositing speed can be improved by reducing the concentration of citric acid or the relativemotion velocity; however, the phosphorus content of the plated layer had no obvious effectsby changing the relative motion velocity.On the basis of the single factor experiment, the orthogonal experiment was adopted infurther optimizing the of Ni-P alloy brush electro-plating process by using the depositingspeed, the phosphorus content, the micro hardness and the bonding force of the plated layeras target. The determined better composition of the plating solution and the technical conditions for the brush electro-plating Ni-P alloy are comprised as follows:280g/L ofNiSO₄·6H₂O,15g/L of NaH₂PO₂·H₂O,25g/L of C₆H₅O₇·H₂O,20g/L of Na₃C₆H₅O₇·H₂O,18g/L of Na₂SO₄,20ml/L of CHCOOH, proper amount of NaC₁₂H₂₅SO₄, PH value of3,working voltage of10V, working temperature of about45℃and relative motion velocity of14m/min.The optimized Ni-P alloy brush plated layer was subjected to an appearance test, ametallographic test, an EDX analysis, an SEM analysis, an XRD analysis and a mechanicalproperty test and the like. The results indicated that the plated layer surface is in a cell-likestructure and the microstructure of the cross section is in a belt-like structure; the platedlayer has the phosphorus content of11.75%and is in an amorphous structure; the porosityof the plated layer is low and the pores of the plated layer with thickness of more than10μmalmost disappear; the micro hardness of the plated layer is up to580HV and is up to980HV after being subjected to the heat treatment at400℃; after65times of thermal shockexperiments, the plated layer did not fall off or peel.In this paper, the wear resistances, the friction coefficients and the corrosion resistanceof the Ni-P alloy plated layer, the quick nickel plated layer and the304stainless steel werecompared. The results indicated that the wear resistance of the Ni-P alloy plated layer isequivalent to that of the quick nickel plated layer and is1.5times that of the304stainlesssteel. The friction coefficient of the Ni-P alloy plated layer is0.375and is significantlylower than that （0.6） of the quick nickel plated layer and that of （0.8） of the304stainlesssteel. The wear resistance of the Ni-P alloy plated after the heat treatment is2.5times of the304stainless steel, and the friction coefficient of the Ni-P alloy plated layer is0.3and issignificantly lower than that （0.55） of the quick nickel plated layer subjected to the heattreatment. The corrosion resistance of Ni-P plated layer is inferior to the corrosionresistance of the304stainless steel in nitric acid medium, and remarkably superior to thecorrosion resistance of the304stainless steel in hydrochloric acid medium and superior tothe corrosion resistance of the304stainless steel in alkali and salt medium. The corrosionresistance of the Ni-P alloy plated layer subjected to the heat treatment is declined; and thecorrosion resistance of the quick nickel plated layer is inferior to that of the Ni-P alloyplated layer and the stainless steel in various corrosive media.