TAN Yong，LIU Chang-sheng，YU Xiao-zhong

(1.Key Laboratory for Anisotropy＆Texture of Materials，Ministry of Education，Northeastern University，Shenyang 110004，China; 2.School of Environmental and Chemical Engineering，Shenyang Ligong University，Shenyang 110159，China)

The surface roughness and microstructure of Ni doped with WC particles co－deposition coating

TAN Yong1，2，LIU Chang-sheng1，YU Xiao-zhong1

(1.Key Laboratory for Anisotropy＆Texture of Materials，Ministry of Education，Northeastern University，Shenyang 110004，China; 2.School of Environmental and Chemical Engineering，Shenyang Ligong University，Shenyang 110159，China)

The intermediate layer was prepared by nickel doped with WC particles electroplating.The parameters，including current density and temperature，were studied.The measured methods，which consisted of surface roughometer and SEM，were used to character the roughness and micrograph.Based on the results，it was shown that the optimized parameters of the composite were as follows，temperature 65℃，current density 5 A/dm2and pH 6.5.In the range of optimized parameters，the roughness Ra was from 4.5 to 6.7 μm.From the SEM micrograph，the particles on the surface were well distributed.The nickel content，which affected the binding force，was determined by the electroplating time.

surface texturing;composite electroplating;WC particle;surface roughness

As a common use material，the cold roller with certain texturing surface is a very important base material used in automobile industry and other fields［1］. The texturing steel can insure the lubricating oil，which located in the concaves，to keep the obturation state.Because of the cushion effect between the steel and the milling tool，the wear performance of the steel increases.Furthermore，the steel with texturing also has the well performance of coating［2］.

With the rapid development of automobile，the quality requiring ofcrustsheetofautomobile，including reflection definition and deep pressing，was higher than before.In order to produce high quality steel sheet，the roller must be treated by texturing.Though having high appending worthiness of the cold texturing steel sheet，the shortage of the production methodsand techniquesbecomethe barrierfor the practicaluse. The traditional treatment methods could decrease the use properties of the steel sheet.The surface of the roller consists of easy－to－broken peaks and easy－to－wear peaks.These peaks affect the roughness and wear performance seriously.The rapid attenuation of the roughness on the surface is the main reason of replacing the roller［3］.Exploiting new methods to produce cold texturing roller become the exigent requirement for cold roller industry.

Generally speaking，the texturing methods consist of shot blast texturing(SBT)，electrical discharge texturing(EDT)and laser beam texturing (LBT)［4～7］.All of the three texturing methods can make the roller surface fall off to form aculeate and concave surface.The roughness of the manufactured texturing rollers attenuated rapidly inducing lower using life because of the effect of cold roller’s material.The amount of the concaves on the surface of cold roller are higher than that of heaves.

The technique of multi－electroplating texture on cold rollis a process ofelectrochemical deposition［8，9］.In this paper，the intermediate layer was prepared by electroplating of nickel doped with high hardness particles.The chrome－plated coating was as the top coating.The nickel base layer couldeliminate the brittleness and internal stress between chrome－layer and substrate to enhance bond strength among the top coatings and substrate［10］.The particles inside the intermediate layer could make the surface of roller maintain roughness and enhance the ductility and wear－resisting properties.The randomly distributed pits in the frosted roller had the good performances such as high density peaks，fine retentivity，higher transmissibility of Ra/PC and reproducibility.

1 Experimental details

The substrate is interstitial free sheet steel(IF steel)of 70 mm×20 mm×1 mm.The size of the used WC particles are 5～20 μm.The micrograph of the particles are shown in Fig.1.

Fig.1 The micrograph of the WC particles

Orthogonal experiments were used to optimize the parameters of technique process for the middle layer.The parameters of technique process included current density and electrolyte temperature.The hard chromium electroplating was prepared as the top coating.The electroplating time was 1.5 h.The SS—550 scanning electron microscopy(SEM)was used to character the surface of the coatings.The surface roughometer(MAHR，German)was used to measure the roughness of the surface.

2 Results and discussion

2.1 Effect of current density on roughness

It could be seen from Fig.2 that the roughness of the electroplating layer decreased to the lowest when the current density was 3.3 A/dm2，and then increased with the increasing of current density.

Fig.2 Effect of current density on roughness roughness for middle layer

In the electroplating process，the electroplating ratio of nickel increased with the current density increasing.The electroplated WC particles were embedded into the electroplating layer to induce the decreasing of surface roughness.On the other hand，the static gravitational force between the substrate surface and the particles increased with current density increasing.The increased static gravitational force accelerated the co－deposition of metal and particles.When the current density was further increasing，the rate ofWC particles in the electroplating layer was less than the rate of base metal nickel electroplating.The low conductivity particles in the multi－electroplating layer covered the part of cathode surface.Because of reducing cathode area，the metal deposition was encumbered on the substrate.The roughness，mainly caused by the particles， increased with current density increasing.

2.2 Effect of electrolyte temperature on roughness

Based on the analysis of Fig.3，it was shown that the roughness of the sample increased with electrolyte temperature increasing.While the metal electroplating ratio decreased with the increasing of temperature.The reduction of metal electroplating induced the decreasing of the embedding deepness for the WC particles in the coating to increase the roughness sequentially.Generally，there are two factors to affect the co－deposition coating.One is that the physics properties，which consisted of electrolyte viscosity and particles moving speed，can be changed by the temperature.Another is that the highertemperature can change the charge of particles surface to affectthe co－ deposition coating.

Fig.3 Curve of electrolyte temperature on

2.3 Micrograph of Ni－WC particles codeposition coatings

The micrograph shown in Fig.4 was obtained by the parameters listed as follows，current density 5 A/dm2，electrolyte temperature 65℃ and pH 6.5.The WC particles were distributed uniformly in the nickel coatings.The uniform distribution could make the surface keep certain roughness.It could be also seen from the figure that the particles were well combined with the nickel coatings.

2.4 Three－dimensional micrograph of coatings and roughness

Based on the observation of three－dimensional micrograph of coating(Fig.5)，it was shown that the particles were distributed stochastically. The stochastic distribution of the particles could make the texturing surface possess the stochastic distribution roughness.

2.5 Section micrograph analysis of chromium electroplating

Fig.6 showed the section micrograph of chromium electroplating with the parametersof temperature 50 ℃，current density 40 A/dm2，electroplating time 1.5 h and pH 6.5.The middle layer was covered by the top chromium coatings completely. There were some different size“islands”on the surface of coatings.The“islands”distributed uniform and stochastic on the top coatings on account of the different size of particles existed in the middle coatings.The roughness of the top chromium coatings was stochastic according to the distribution of particles in the middle coatings.The excellent texturing could assure that the concaves appeared on the surface of the roller when rolling to obtain well rolling and coating effects.

Fig.4 Micrograph of nickel/WC particles coatings

Fig.5 Three－dimensional micrograph of coatings and roughness

ig.6 Section micrograph of chromium electroplating

When increasing electroplating time， the roughness decreased.The surface roughness of the nickel－WC particles co－deposition coatings was from 4.5 μm to 6.7 μm in the condition of optimized parameters.When deposited chromium coatings for 1.5 h，the surface texturing roughness was from 1.35 μm to 4.47 μm.

3 Conclusion

The electrolyte temperature was the most factors to prepare Ni－WC co－deposition coating.The WC particles were distributed uniformly in the intermediate nickel coatings. The uniform distribution could make the surface keep certain roughness.In the condition of optimized parameters，the surface roughness of the nickel－WC particles co－deposition coatings was from 4.5 μm to 6.7 μm.There are many uniform “islands” distributed stochastic on the surface when chromium coatings deposited.

［1］Yan Yonggen.Status and development of coldroller texturing［J］.Bao steel technology，1995(6):45－50.

［2］Lin H S.A mixed lubrication model for cold strip rolling［D］.Shenyang:Northwestern University，1998.

［3］EI－Menshawy F，Snaith B.Advances in electro－discharge texturing(EDT)for cold mill workrolls［J］.Iron and Steel Engineer，1991，63(8):52－59.

［4］Wilson G，Parker C.The use of EDT textured rolls in a wide range of applications［C］//44 th MWSP Conference Proceedings，Vol.XL，2002:889－898.

［5］Utsch M，Vinke.P.EDT－roll technology as a base of modern surfaces in automotive cold mill flat products［C］//MS＆T 2004 Conference Proceedings.599－607.

［6］Oktay Elkoca.A study on the characteristics of electrical discharge textured skin pass mill work roll［C］.Surface＆Coatings Technology，2008:2765－2774.

［7］Simao J，Aspinwall D K.Mill roll texturing using EDT［J］.J Mater Process Technol，1994，45(5):207－214.

［8］Shafik M，Knight J A G.Development of a new generation of electrical discharge texturing system using an ultrasonic motor［C］//Proceedings of the 13th International Symposium for Electromachining ISE MXIII，2001，Spain:903－923.

［9］Andrzej Lasia，Li Zhaojiang，Rod Barr.Method of manufacture of electrochemically textured surface having controlled peak characteristics:U S，Pat Appl.6478943［P］.2002，Nov.12.

［10］DamienDeSoete，Donald Pans，KurtSteinhoff.EBT technology and its applications［J］.Iron and Steel Engineer，1997(9):36－40.

TG 156

A

1671-6620(2011)01-061-04

2010-07-07.

譚勇 (1969—)，男，遼寧沈陽人，東北大學博士研究生，E－mail:tanyong@126.com;劉常升 (1963—)，男，內(nèi)蒙古奈曼旗人，東北大學教授，博士生導師.