Study On The Properties Of Ni-Fe-Cr-P Alloy Coating By Electroplating

Metal material is the most widely used most in the world, use of materials, including ironand steel materials, with its huge reserves, low price, the advantages of easy shaping becamethe support frame of modern industrial. But for plain steel production a large share of the ironand steel materials (such as Q235steel), because of its poor corrosion resistance, each year aconsiderable waste of resources caused by corrosion problems, and because of corrosioncaused by accidents, the disaster has also been reported. Through the electroplating method inplain steel substrate surface to obtain a better corrosion resistance of metal or alloy coating,can effectively improve the corrosion resistance of material, at the same time, expand the useof the plain steel materials.In this work, the Ni-Fe-Cr-P alloy coating on Q235steel substrate by electroplatingmethod is studied, obtained by orthogonal test and single factor experiments the optimumplating process, using SEM, EDS, XRD and other test methods to study the different processparameters on the alloy electroplating coating surface microstructure, chemical compositionand the influence of the organizational structure, using porosity experiment, Electrochemicalpolarization,electrochemical impedance, immersion test, corrosion resistance of coating wasstudied, and the corrosion mechanism is discussed.In alloy plating porosity as evaluation plating conditions, design L16(45) orthogonal test,and the single factor experiment, the main factors which can obtain the best processconditions for plating Ni-Fe-Cr-P alloy coating: pH3.0, chromium chloride150g/L, cathodiccurrent density of10A/dm2, ferrous sulfate5g/L, plating time30min, plating temperature30℃.With the increase of concentration CrCl3in plating solution, the surface particle size isreduced, but when the concentration of CrCl3is higher than150g/L, the coating becomerough, with micro cracks appear, surface quality decreased obviously. EDS analysis resultsalso indicate that with the increase of concentration CrCl3in plating solution, Cr content inthe alloy coatings increases firstly and CrCl3concentration higher than150g/L the Cr contentreduces. The microhardness of alloy coating increases first and then decreases, when CrCl3concentration achieves150g/L, the microhardness is572HV. XRD test and analys showsthat the alloy coatings obtained by different CrCl3concentration solution arise "steamed breadpeak" in about2θ=45°, an amorphous structure can be judged, and P content in the coatingsare greater than9%, the amorphous coating has nothing to do withand the Cr content.Electrochemical experiments show that in150g/L, the coating possesses the largest polarization resistance, the youngest corrosion current density, and the largest capacitivereactance arc radius, the best corrosion resistance.With the increase of pH, the particle size on the surface decreases first then increases, Crcontent increased first, at pH3.0, no microcracks appear, and the Cr content is most.Electrochemical experiments and the results show that when pH is3.0, the polarizationresistance of alloy coating is biggest, corrosion current density and porosity is minimum,obtain the best corrosion resistance. Increasing the cathodic current density, the thickness ofthe alloy coating always increasing, the Cr content increased first,and at20A/dm2Cr contentis the highest, but at the moment, the micro cracks appear, and the surface becomes rough.Electrochemical experiments and the the results show that when Dkis10A/dm2, thepolarization resistance of alloy coating is biggest, corrosion current density and porosity isminimum, obtain the best corrosion resistance.In different concentration of HCl solution electrochemical experiment shows that withthe increase of the concentration of HCl, the polarization resistance of alloy coatings reduces,the corrosion current density increases, the capacitive reactance arc radius reduces, corrosionresistance becomes worse. It shows that poor corrosion resistance in HCl solution, the activityof Cl-ion is very strong, it could damage the metal surface passivation membrane easily,leading to local corrosion. Soaked in10%HCl solution weightlessness experiment shows thatthe corrosion weight loss perunit area is smaller before5h and after24h found that coatingweight loss of5.8mg/cm2, and the rate of corrosion weightlessness increased significantly,corrosion resistance decreases with the extension of immersion time.Electrochemical experiments in different concentration of NaOH solution shows thatwith the increase of the concentration of NaOH, polarization resistance of alloy coatings isreduced, the corrosion current density increases, the capacitive reactance arc radius reducescorrosion resistance becomes worse. Alloy coating has good corrosion resistance in NaOHsolution, because it’s easily to form passivation film in the alkaline etching solution on thesurface, can play a protective role for the materials, reducing the corrosion speed. Soakedexperiments in10%NaOH solution shows that before20h alloy coating corrosionweightlessness increased fast, corrosion weightlessness increased slower per unit area, thecorrosion reaction speed become slow.