CN108130570A - A kind of compound trivalent plating chromium process - Google Patents

Abstract

The invention provides a metal surface composite chrome plating process and an electroplating solution formula. The method adopts segmentation and sub-tank electroplating process: first, a chromium layer of 20-30um is plated on the metal surface according to a conventional method; Nano-silicon nitride is added to the electroplating solution. Due to the rigidity of nano-silicon nitride itself, it can be uniformly dispersed in the coating during the electroplating process, thereby improving the hardness and wear resistance of the coating. Nano-silicon nitride uniformly dispersed in the coating can on the one hand fill the pores of the coating and wrap around the surface of the chromium metal grains to prevent the infiltration of corrosive liquid; Dunhua, thus improving the corrosion resistance. The metal material is electroplated twice to form a composite electroplating layer. The electroplating layer is evenly distributed on the metal surface and has a hardness of HV900‑1200. It has superior performance and has broad application prospects and economic value.

Description

A Composite Trivalent Electrochrome Plating Process

technical field

The invention belongs to the field of electroplating, and in particular relates to an electroplating process for improving the thickness, surface hardness, corrosion resistance and wear resistance of a chromium plating layer.

Background technique

At present, chrome plating has become one of the most widely used plating types in the electroplating industry. For a long time, chrome plating has adopted the hexavalent chromium electroplating process, in which chromic acid as a provider of hexavalent chromium ions is very toxic, which can cause skin burns and ulcers, and cause workers to suffer from skin rashes, nasal septum perforation and other occupational diseases, and It has a strong carcinogenic effect on the human body. At the same time, it will lead to blockage of soil pores and damage the soil structure. These phenomena have aroused people's widespread concern. With people's increasing awareness of environmental protection, the research of trivalent electroplating chromium and the electroplating process to improve the surface hardness, corrosion resistance and wear resistance of the coating are more and more popular.

However, the current trivalent chromium coating has the following problems:

(1) It is difficult to increase the thickness of the coating: at present, the thickness of the trivalent chromium coating is generally only a few microns. Chromium electrodeposition stops due to hydrogen evolution.

During the electroplating process, trivalent chromium ions are easily oxidized to hexavalent chromium at the anode, which affects the electroreduction of trivalent chromium, resulting in the inability to continue to thicken the coating.

(2) The composition of the plating solution is complex. At present, the plating solution system not only has a great variety, but also contains a large amount of additives. In addition, other metal impurities brought in by the anode make the management and maintenance of the plating solution very difficult, and also limit the popularization and application of trivalent chromium plating.

(3) The conventional trivalent chromium plating technology is currently only applied to decorations due to its limited surface hardness, thickness and wear resistance, and has not yet achieved industrial application.

It is difficult to improve the surface hardness, surface wear resistance and corrosion resistance at the same time by conventional trivalent electroplating technology.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention provides a composite trivalent chromium plating process. The method adopts segmentation and sub-tank electroplating to form a composite trivalent chromium plating layer. In the present invention, boric acid is added in the electroplating solution to stabilize the pH value of the plating solution, and a thermostat is placed below the electroplating tank to stabilize the temperature of the plating solution, which reduces the hydrogen evolution reaction and is beneficial to the thickening of the coating.

Since the titanium-based coating anode has the advantages of convenient use, relatively corrosion resistance, and long service life, coating the titanium base with iridium oxide as the coating anode of the electrode catalytic layer can avoid the formation of hexavalent chromium, and can prevent and eliminate The sludge formed on the anode keeps the bath stable for a long time.

The plating solution of the present invention also contains nano-silicon nitride. Due to the rigidity of the nano-silicon nitride itself, it can be evenly dispersed in the coating during the electroplating process, thereby improving the hardness and wear resistance of the coating;

Nano-silicon nitride uniformly dispersed in the coating can on the one hand fill the pores of the coating and wrap around the surface of the chromium metal grains to prevent the infiltration of corrosive liquid; Dunhua, thus improving the corrosion resistance. The thickness of the coating can reach 50-70um by using the electrochrome plating process. The surface hardness of the coating reaches 900HV-1200HV, and the corrosion resistance and wear resistance both reach the level of the hexavalent coating.

A kind of compound trivalent electroplating chromium process, it is characterized in that with graphite electrode as anode, with the metal substrate that needs electroplating as cathode, electroplating steps are as follows:

Step 1: Degreasing, polishing, washing, and pickling the cathode base body using conventional technical methods in this technical field;

Step 2: Pour electroplating solution 1 into electrolytic tank 1, raise the temperature of electrolytic tank 1 to 30°C, power on the electroplating tank to start electroplating, and plate a chromium coating with a thickness of 20-30um on the metal surface;

Step 3: Secondary electroplating, pour the electroplating solution 2 into the electrolytic tank 2, raise the temperature of the electroplating solution 2 to 30°C, and place a constant temperature magnetic stirrer under the electroplating tank 2; The metal surface is cleaned again, placed in the second electrolytic tank for secondary electroplating, and the constant temperature magnetic stirrer is turned on, and a chromium plating layer containing nano-particles Si ₃ N ₄ is formed again on the surface of the coating;

Among them, the composition of electroplating solution 1 is: Cr ³⁺ 04-0.8mol·dm ^-3 , HCOOH 0.4-1.0mol·dm ^-3 , CH ₃ OH 0.2-0.5mol·dm ^-3 , NH ₄ Br 0.2-0.3mol ·dm ^-3 , Na ₂ SO ₄ 1.5-2.0mol·dm ^-3 , H ₃ BO ₃ 0.8-1.2mol·dm ^-3 , C ₁₂ H ₂₅ SO ₄ Na 0.005mol·dm ^-3 ;

The composition of electroplating solution 2 is: Cr ³⁺ 04-0.8mol·dm ^-3 , HCOOH 0.4-1.0mol·dm ^-3 , CH ₃ OH 0.2-0.5mol·dm ^-3 , NH ₄ Br 0.2-0.3mol·dm ^-3 , Na ₂ SO ₄ 1.5-2.0mol·dm- ³ , H ₃ BO ₃ 0.8-1.2mol·dm- ³ , C ₁₂ H ₂₅ SO ₄ Na 0.005mol·dm- ³ , Si ₃ N ₄ 2-8g ·L- ¹ .

Further, the content of Si ₃ N ₄ with a particle size of 20-50 nm in the second plating solution is 4-8 g/L.

Further, the preparation method of the electroplating solution 2 is as follows: dissolving the reagents of each raw material component in water, then dissolving the metered nano-silicon nitride in it, mixing evenly, and dispersing with ultrasonic waves. The ultrasonic dispersion power is 600-1000w, and the ultrasonic dispersion time is 5-6min.

A trivalent chromium plating process of the present invention uses a graphite electrode as an anode, the graphite material is convenient to obtain, the price is cheap, the electroplating efficiency and the electroplating effect are very good, and the material requiring chrome plating is used as the cathode, and the cathode substrate is degreased before electroplating , polishing, washing, pickling and other treatments. Ensure that the coating obtained during electroplating has sufficient adhesion. Water-insoluble nano-solid particles Si3N4 are added to the electroplating solution, and they are co-deposited with the main metal on the substrate during the electroplating process. These particles are dispersed in the coating and can effectively refine the metal grains to improve the mechanical properties of the metal. performance and corrosion resistance.

The reaction principle of the trivalent chromium plating of the present invention is as follows: the electroreduction of negative Cr ³⁺ is divided into two parts, wherein the first step is the single-electron quasi-reversible reaction of Cr ³⁺ , which has the characteristics of catalytic reaction, that is, the generated Cr ^{2 +} can be re-oxidized to Cr ³⁺ by H ⁺ in the solution (reaction 1-1); the second step is the irreversible reaction of Cr ²⁺ reduction to metallic Cr (reaction 2-7).

Cr ³⁺ +e ^- → Cr ²⁺ (1-1)

Cr ²⁺ +2e ^- → 2Cr (1-2)

At the anode, mainly water is discharged to generate oxygen, and chlorine ions to generate chlorine gas. At the same time, formic acid in the electrolyte complexes with chromium ions to form relatively stable complex ions, which makes trivalent chromium ions easier to discharge and promotes the deposition of metal chromium. The HCOO ^- ligands provided by formate are able to form complexes with Cr ³⁺ , thereby adjusting the discharge potential of complex ions. At the same time, formic acid can also act as a buffer in the plating solution. Boric acid keeps the pH of the plating solution within a certain range during the electroplating process. Sulfates increase the conductivity of the bath and lower the cell voltage.

In the present invention, the formation of nano-silicon nitride in the composite coating includes a two-step adsorption process: the first step is weak reversible physical adsorption, that is, the surface is carrying particles of ions and solvent molecules adsorbed on the cathode surface; the second step is strong irreversible physical adsorption Electrochemical adsorption, that is, as part of the ions adsorbed on the surface are reduced, the particles and the cathode undergo strong adsorption and enter the coating.

The hardness of the composite electroplating layer formed by the composite trivalent electroplating chromium plating process provided by the present invention reaches HV900-1200. Since the outermost chromium plating layer contains nano-particles Si ₃ N ₄ ,

Therefore, its wear resistance and corrosion resistance are twice that of conventional coatings. Physical properties, coating structure optimization, mechanical properties are also optimized.

The energization steps of step 2 and step 3 of the chromium plating method of the present invention are carried out according to common technical methods in this technical field, and the forward current is determined according to the surface area of the workpiece, generally 25-33A/dm ² . The time of forward current depends on the thickness of the coating.

The chrome-plating method of the present invention is applicable to metal materials, steel products and the like commonly used in the machinery industry.

Description of drawings

Fig. 1 is a structural diagram of the device of the present invention,

①Suction device, ②Titanium substrate anode coated with iridium oxide, ③Constant temperature magnetic stirrer, ④Constant temperature magnetic stirrer, ⑤Plating parts, ⑥DC stabilized voltage power supply

Detailed ways

Embodiment one:

Specific operation:

Configure electroplating solution 1 and electroplating solution 2 according to the following formula:

Plating solution 1: CrCl ₃ .6H ₂ O 106g/L, CHooH 9.2g/L;

Plating solution two: CrCl ₃ .6H ₂ O 110g/L, CHooH 9.8g/L, Si ₃ N ₄ 6g·L ^-1 .

Follow the steps below to electroplate metal materials:

Step 1: Degreasing, polishing, water washing and pickling treatment are carried out on the metal surface by adopting conventional technical methods in this technical field, so as to activate the metal surface.

Step 2: Pour electroplating solution 1 into electrolytic tank 1, raise the temperature of electrolytic tank 1 to 30°C, and put the surface-activated metal in step 1 into electrolytic tank 1. The electroplating tank is energized to start electroplating. After electroplating for 5 minutes, a chromium coating with a thickness of 20-30um is plated on the metal surface.

Step 3: Secondary electroplating, pour the electroplating solution 2 into the electrolytic tank 2, raise the temperature of the electroplating solution 2 to 30°C, and place a constant temperature magnetic stirrer under the electroplating tank 2. Clean the surface of the chrome-plated metal in step 2, place it in the electrolytic tank 2 for secondary electroplating, and turn on the constant temperature magnetic stirrer, and keep the rotating speed at 200r/min. After electroplating for 10 minutes, a chromium plating layer containing nano-particles Si ₃ N ₄ is formed again on the surface of the plating layer. ·

Embodiment two:

Specific operation:

Configure electroplating solution 1 and electroplating solution 2 according to the following formula:

Plating solution 1: CrCl ₃ .6H ₂ O 106g/L, CHooH 9.2g/L;

Plating solution two: CrCl ₃ .6H ₂ O 110g/L, CHooH 9.8g/L, Si ₃ N ₄ 8g·L ^-1 .

Follow the steps below to electroplate metal materials:

Step 1: Degreasing, polishing, water washing and pickling treatment are carried out on No. 45 steel sheet (3cm×4cm, thickness 2mm) by using conventional technical methods in this technical field, so as to activate the metal surface.

Step 2: Pour electroplating solution 1 into electrolytic tank 1, raise the temperature of electrolytic tank 1 to 30°C, and put the surface-activated metal in step 1 into electrolytic tank 1. The electroplating tank is energized to start electroplating. After electroplating for 5 minutes, a chromium coating with a thickness of 20-30um is plated on the metal surface.

Step 3: Secondary electroplating, pour the electroplating solution 2 into the electrolytic tank 2, raise the temperature of the electroplating solution 2 to 30°C, and place a constant temperature magnetic stirrer under the electroplating tank 2. Clean the surface of the chrome-plated metal in step 2, place it in the electrolytic tank 2 for secondary electroplating, and turn on the constant temperature magnetic stirrer, and keep the rotating speed at 300r/min. After electroplating for 10 minutes, a chromium plating layer containing nano-particles Si ₃ N ₄ is formed again on the surface of the plating layer.

Embodiment three:

Specific operation:

Configure electroplating solution 1 and electroplating solution 2 according to the following formula:

Plating solution 1: CrCl ₃ .6H ₂ O 101g/L, CHooH 9.1g/L;

Plating solution two: CrCl ₃ .6H ₂ O 110g/L, CHooH 9.8g/L, Si ₃ N ₄ 6g·L ^-1 .

In this embodiment, a red copper plate test piece with a purity of 99.9% is used, its specification is 3cm×4cm, and its thickness is 2mm, and its metal material is electroplated:

Step 1: Degreasing, polishing, water washing and pickling treatment are carried out on the metal surface by adopting conventional technical methods in this technical field, so as to activate the metal surface.

Step 2: Pour electroplating solution 1 into electrolytic tank 1, raise the temperature of electrolytic tank 1 to 30°C, and put the surface-activated metal in step 1 into electrolytic tank 1. The electroplating tank is energized to start electroplating. After electroplating for 5 minutes, a chromium plating layer with a thickness of 20-30um is plated on the surface of the copper plate.

Step 3: Secondary electroplating, pour the electroplating solution 2 into the electrolytic tank 2, raise the temperature of the electroplating solution 2 to 30°C, and place a constant temperature magnetic stirrer under the electroplating tank 2. Clean the surface of the chrome-plated metal in step 2, place it in the electrolytic tank 2 for secondary electroplating, and turn on the constant temperature magnetic stirrer, and keep the rotating speed at 400r/min. After electroplating for 10 minutes, a chromium plating layer containing nano-particles Si ₃ N ₄ is formed again on the surface of the plating layer. ·

Embodiment four:

Specific operation:

Configure electroplating solution 1 and electroplating solution 2 according to the following formula:

Plating solution 1: CrCl ₃ .6H ₂ O 110g/L, CHooH 9.6g/L;

Plating solution two: CrCl ₃ .6H ₂ O 110g/L, CHooH 9.6g/L, Si ₃ N ₄ 8g·L ^-1 .

Follow the steps below to electroplate 304 stainless steel metal materials:

Step 1: Degreasing, polishing, water washing and pickling treatment are carried out on the metal surface of 304 stainless steel (3cm×4cm, thickness 2mm) by adopting conventional technical methods in this technical field, so as to activate the metal surface.

Step 2: Pour electroplating solution 1 into electrolytic tank 1, raise the temperature of electrolytic tank 1 to 30°C, and put the surface-activated metal in step 1 into electrolytic tank 1. The electroplating tank is energized to start electroplating. After electroplating for 5 minutes, a chromium coating with a thickness of 20-30um is plated on the metal surface.

Step 3: Secondary electroplating, pour the electroplating solution 2 into the electrolytic tank 2, raise the temperature of the electroplating solution 2 to 30°C, and place a constant temperature magnetic stirrer under the electroplating tank 2. Clean the surface of the chrome-plated metal in step 2, place it in the electrolytic tank 2 for secondary electroplating, and turn on the constant temperature magnetic stirrer, and keep the rotating speed at 600r/min. After electroplating for 10 minutes, a chromium plating layer containing nano-particles Si ₃ N ₄ is formed again on the surface of the plating layer. ·

Comparative example:

Except that silicon nitride is not contained in the plating solution, other conditions are the same as in Example 2.

Result analysis:

Coating corrosion resistance test:

Use a Vickers hardness tester (with a load of 100kg), the angle of the cone surface is 136° to press the diamond square pyramid, pay attention to ensure that the depth of the indenter should be less than one-tenth of the surface thickness, and keep it for 15s to measure the hardness of the coating. During the test, take the indentation hardness values of the top, bottom, left, right and middle points, and then take the average value.

Coating corrosion resistance test:

Using the full immersion weight loss test method, the composite coating samples were respectively immersed in 20% NaOH solution and 3.5% NaCl solution, and the duration of the erosion test was 240h and 340h respectively, while maintaining the temperature of the corrosion medium at 30°C, and then The weight loss after corrosion was measured to obtain the corrosion rate. The samples before and after corrosion were rinsed with deionized water, ultrasonically cleaned with ethanol, vacuum dried, and weighed. The corrosion rate is calculated according to the following formula: corrosion rate=(mass before corrosion-mass after corrosion)/(corrosion time×corrosion surface area).

Wear resistance test:

The friction and wear test is carried out on the SRV wear testing machine. The grinding sample is a quenched steel ball of chromium-containing steel with a diameter of 10nm. The Rockwell hardness is 58-60, and the surface roughness of the steel ball is less than 0.4um. Under the condition of no lubrication and no abrasive, the quenched steel ball slides back and forth on the chrome-plated surface, the stroke is 2mm, the frequency is 30Hz, and the load is 60N.

Coating Thickness Test:

Using the weighing method. Specifically, after polishing, degreasing, washing, drying and other processes, the plated parts are weighed, and then electroplated. The mass after - the mass of the plated piece before electroplating)/(the surface area of the part covered by the plating layer × the density of the plated metal), the unit of the surface area is cm ² , the unit of mass is g, and the unit of the density of the plated metal is g/ml.

Embodiment one, two and the test result of comparative example coating performance are as follows:

As can be seen from the above table, the coating thickness and Vickers hardness of the first and second embodiments are obviously higher than those of the comparative example, and the wear amount and corrosion rate in 30 minutes are obviously better than those of the comparative example. This shows that nano-particle silicon nitride significantly improves the hardness, wear resistance and corrosion resistance of the coating.

Claims (3)

1. a kind of compound trivalent plating chromium process, it is characterised in that using graphite electrode as anode, to need the metallic matrix being electroplated For cathode, plating step is as follows：

Step 1：Oil removing, polishing, washing, pickling processes are carried out to cathode base using the art conventional technique method；

Step 2：Electroplate liquid one is poured into electrolytic cell one, the temperature of electrolytic cell one is raised to 30 DEG C, is powered to electroplating bath Start to be electroplated, the chrome plating that thickness is 20-30um is plated in metal surface；

Step 3：Second time electroplating pours into electroplate liquid two in electrolytic cell two, and the temperature of electroplate liquid two is raised to 30 DEG C, and A constant temperature blender with magnetic force is put below electroplating bath two；The metal of chromium plating in step 2 is subjected to surface clean again, is put Second time electroplating is carried out, and open constant temperature blender with magnetic force in merging electrolytic cell two, formed again containing nanometer on the surface of coating Particle Si₃N₄Chrome layer；

The ingredient of wherein electroplate liquid one is：Cr³⁺04-0.8mol·dm^-3, HCOOH 0.4-1.0moldm^-3, CH₃OH 0.2- 0.5mol·dm^-3, NH₄Br 0.2-0.3mol·dm^-3, Na₂SO₄ 1.5-2.0mol·dm^-3, H₃BO₃ 0.8-1.2mol·dm^-3, C₁₂H₂₅SO₄Na 0.005mol·dm^-3；

The ingredient of electroplate liquid two is：Cr³⁺04-0.8mol·dm^-3, HCOOH 0.4-1.0moldm^-3, CH₃OH 0.2- 0.5mol·dm^-3, NH₄Br 0.2-0.3mol·dm^-3, Na₂SO₄ 1.5-2.0mol·dm^-3, H₃BO₃ 0.8-1.2mol·dm^-3, C₁₂H₂₅SO₄Na 0.005mol·dm^-3、Si₃N₄ 2-8g·L^-1。

2. a kind of compound trivalent plating chromium process according to claim 1, it is characterised in that granular size is in plating solution two The Si of 20-50nm₃N₄Content is 4-8g/L.

A kind of 3. compound trivalent plating chromium process according to claim 1, it is characterised in that the preparation of the electroplate liquid two Method is：The reagent of each raw material components is soluble in water, then be dissolved in the nano-silicon nitride is measured wherein, after mixing Disperseed with ultrasonic wave.The ultrasonic wave dispersion power is 600-1000w, and the time of ultrasonic wave dispersion is 5-6min.