Research On Electroplating High Iron-Low Tin-Znic Alloy And Its Properties Of Coating

The Protective decorative plating coatings are widely used in the equipments and parts in the machinery,engineering,hardware and others.Electroplating chromium,copper,nickel and other metals and their alloys have corrosion resistance and metallic luster,and are commonly used as protective decorative plating layer.However,heavy metals,chromium,copper,nickel and others have adverse effects on the environment and human’s body during the electroplating process and use procedure.So it is vital to develop protective and decorative plating coating and electroplating technology,which are friendly to the environment and our body.In this thesis,iron,tin and zinc,which were non-toxic to humans,were selected.The goal was to obtain a high-iron alloy plating layer with a mass fraction of iron greater than 60 wt%,which has the effect as decorative chromium plating.The plating process conditions of the high Fe-low Sn-Zn alloy were investigated to obtain an alloy coatings with different contents in different plating systems and process conditions,and the properties of the obtained alloy coatings were tested and analyzed.By experiments,the four plating systems of chloride,sulfate,fluoroborate and amino-sulfonate were researched.To investigate the stability of the plating solution,the four solutions containing 50 g·L-1 Fe2+ at 25℃,pH1 corresponding to above four plating systems were configured.In the absence of reducing agent,the rate of Fe3+production in the three systems of chloride,sulfate,fluoroborate increased significantly as the temperature,pH,and ionic concentration increased.Only Fe3+ concentration in amino-sulfonate was decacreasing while the ionic concentration increased.Added the reducing agents of iron powder and ascorbic acid could significantly reduce the content of Fe3+.By Hull and Haring cell experiments,the optimal process for four plating systems of chloride,sulfate,fluoroborate and amino-sulfonate were obtained:The optimal composition of the plating solution and process conditions of the chloride system was 80 g·L-1 FeCl2·4H2O,0.1-0.3 g·L-1 SnCl2·2H2O,2 g·L-1 ZnCl2·2H20,10 g·L-1 NaCl,3.5-7 g·L-1 H3BO3,2.5 g·L-1 NH4Cl,1 g·L-1 ascorbic acid,0.2-0.5 g·L-1 ferrous powder,2.2-4.2 g·L-1 refinement agent ME-1,0.5-1 g·L-1 Stress attenuator SA-1,0.2 g·L-1 brightening agent MB-1,0.2 g·L-1 surface active agent SR1,temperature 40℃,pH 4.5,current density 6-12 A·dm-2,stirring speed 100 r·min-1,silver-white bright plating coating was obtained.The optimal composition of the plating solution and process conditions for the sulfate system was 150 g·L-1 FeSO4·7H2O,0.3-0.5 g·L-1 SnSO4,5 g·L-1 ZnSO4·7H2O,100 g·L-1 Na2SO4,10 g·L-1 NaCl,7 g·L-1 H3BO3,2 g·L-1 ascorbic acid,1-2g·L-1 ferrous powder,10 g·L-1 grain refiner ME-2,4.5-5 g·L-1 brightening agent MB-2,0.5 g·L-1 surface active agent SR-1,temperature 35-40℃,pH 4,current density 2.5-6.5 A·dm-2,stirring speed 100-300 r·min-1,the silver-white plating coating obtained was flat and bright.The optimal composition and process conditions of the fluoroborate system was 0.70 mol·L-1 Fe(BF4)2,0.2 g·L-1 SnCl2·2H2O,2 g·L-1 Zn(BF4)2,30g·L-1 NaBF4,20g·L-1 H3BO3,10 g·L-1 NaCl,10 mL·L-1 HBF4,2g·L-1 NH4BF4,2 g·L-1 ascorbic acid,0.5 g·L-1 ferrous powder,0.1g·L-1 surface active agent SR-1,temperature 40℃,pH 4,current density 3-5 A·dm-2,stirring speed 100 r·min-1,silver-white bright plating coating was can obtain.The optimal composition and process conditions of the plating solution of the amino sulfonate system was 440-520 g·L-1(NH2SO3)2Fe,0.8 g·L-1 SnCl2·2H2O,4 g·L-1 ZnCl2·7H2O,30 g·L-1 H3BO3,15 g·L-1 NH2SO3H,10 g·L-1 NaCl,3 g·L-1 ascorbic acid,0.5 g·L"1 ferrous powder,current density 10-12 A·dm-2,temperature 40℃,pH 34,tirring speed 100-300 r·min-1,the silver-white plating obtained was flat and bright.The coatings obtained by the optimal plating process and solution composition in above four plating systems were flat and bright.The mass fraction of iron was higher than 60 wt%respectively.The properties of the plating coatings were examined by checking the appearance,thickness,hardness and corrosion resistance of the coatings respectively.The results showed that the total property at same condition was:sulfamate system>fluoroborate system>sulfonate system>chloride system.For above chloride system,another brightening agent MB-2 was added in plating solution.When the specimen pre-plated nickel was plated in this solution,the element content of the plating alloy coating obtained did not change much,however,the hardness and corrosion resistance increased.With plating time increasing,the crystal surface orientation of iron element grew from BCC(110)to BCC(200)and(221).The corrosion resistance of plating coating was enhanced.