CN101892471B - Chemical nickel plating process of Mg-Gd-Y-Zr magnesium alloy - Google Patents

Abstract

The invention relates to a method for electroless nickel plating on a Mg-Gd-Y-Zr (wt.%) magnesium alloy. The method is to pretreat the magnesium alloy substrate before plating, and then deposit electroless nickel by electroless nickel plating layer. The pre-plating pretreatment includes five steps of degreasing, activation, pickling, reactivation and zinc immersion; the electroless nickel plating solution adopts basic nickel carbonate as the main salt, and sodium hypophosphite as the reducing agent. Hydrofluoric acid is used as a corrosion inhibitor, lactic acid is used as a complexing agent, and a mixture of cadmium sulfate and potassium iodate is used as a brightener. Plating is applied at about 85°C after galvanizing, and a bright, smooth, uniform and dense nickel plating layer can be obtained. The invention is suitable for performing electroless nickel plating on the surface of Mg-Gd-Y-Zr magnesium alloy so as to achieve the purpose of protecting the magnesium alloy. The invention has the advantages of fast plating speed, good protection, simple operation and easy control.

Description

A Mg-Gd-Y-Zr magnesium alloy electroless nickel plating process

technical field

The invention relates to a Mg-Gd-Y-Zr magnesium alloy electroless nickel plating process, which belongs to the field of metal corrosion and protection.

Background technique

Magnesium alloys have excellent properties such as high specific strength, good impact resistance, and light weight, making them have broad application prospects in aerospace, electronics, and automotive industries. However, magnesium alloys have high chemical activity and are prone to corrosion, so their poor corrosion resistance restricts their further popularization and application. Therefore, magnesium alloys must be subjected to surface protection treatment before practical application. Electroless nickel plating is one of the simplest and most economical surface protection technologies widely used, which can make magnesium alloys obtain good corrosion resistance and wear resistance, as well as weldability and electrical conductivity as well as metallic texture and appearance .

Studies have shown that Mg-Gd-Y-Zr alloys have the advantages of high specific strength, high specific modulus, corrosion resistance, easy welding, and good heat resistance. Magnesium alloy, and the strength of the alloy is very high, it can partially replace aluminum alloy for weight reduction in the field of aerospace, and has a good development prospect. However, there are very few research reports on the surface protection technology of Mg-Gd-Y-Zr alloys. Magnesium alloys are difficult-to-plate substrates, so pre-plating pretreatment is necessary, and the substrate has a great influence on pre-treatment. The existing pre-treatment methods are not suitable for Mg-Gd-Y-Zr magnesium alloys, resulting in Many problems occurred during the process, such as partial failure to be plated, and defects such as peeling and bubbling. Therefore, finding a suitable pretreatment method for Mg-Gd-Y-Zr magnesium alloy is beneficial to the subsequent electroless nickel plating process.

Contents of the invention

The purpose of the present invention is to make up for the deficiencies of the existing chemical nickel plating process, and proposes a method for chemical nickel plating aimed at the surface protection of Mg-Gd-Y-Zr magnesium alloys. Good sex and bonding.

The purpose of the present invention is achieved by the following technical solutions: a Mg-Gd-Y-Zr magnesium alloy electroless nickel plating method, comprising the following steps:

A. Pretreatment before plating:

Degreasing, activating, pickling, reactivating and galvanizing are performed on the magnesium alloy substrate first. The degreasing solution is sodium carbonate 30g/L, sodium phosphate 30g/L and OP-101-2ml/L, the operating temperature of the solution is 60-80°C, and the processing time is 1min; the activation solution is chromium oxalate 92g/L, and the operating temperature is room temperature , the treatment time is 30s; the pickling solution is nitric acid 90ml/L and chromic acid 90g/L, the solution operating temperature is room temperature, and the treatment time is 90-150s; the reactivation solution is chromium oxalate 92g/L, the operating temperature is room temperature, and the treatment The time is 5-10s; the zinc dipping solution is zinc oxide 20-30g/L, hydroxyethylene diphosphoric acid 70-80ml/L, ethylenediamine 12-18ml/L and phosphoric acid 8-10ml/L; the operating temperature is 82 -86°C, pH value 9.2-9.6, treatment time 1min;

B. Carry out electroless nickel plating and passivation treatment. The nickel plating solution adopts basic nickel carbonate as the main salt, sodium hypophosphite as the reducing agent, lactic acid as the complexing agent, hydrofluoric acid as the corrosion inhibitor, cadmium sulfate and Potassium iodate is used as a brightener, and finally passivated.

The nickel plating solution is composed of basic nickel carbonate 12-18g/L, sodium hypophosphite 25-35g/L, hydrofluoric acid 40-50ml/L, lactic acid 28-35ml/L, brightener 3.5-5ml/L, The operating temperature of the nickel plating solution is 82-86°C, the pH value is 4.5-5.0, and the treatment time is 2 hours.

The brightener is composed of 2-3mg/L cadmium sulfate and 5.5-7.5mg/L potassium iodate.

The passivation solution is chromic anhydride 50g/L, the operating temperature is 82-86°C, and the treatment time is 5min.

Rinse with water for 30s between the steps of degreasing, activation, pickling, reactivation, zinc dipping and electroless nickel plating.

Compared with the prior art, the present invention has the following advantages: 1. The electroless nickel plating of Mg-Gd-Y-Zr magnesium alloy is carried out by using the existing pretreatment method and plating solution, and the parts that are prone to occur cannot be plated or even peeled , bubbling and other phenomena, resulting in poor performance of the coating, weak binding force, and cannot play a protective role. And the present invention carries out big improvement on the pretreatment method according to the self characteristic of Mg-Gd-Y-Zr magnesium alloy, innovates a set of electroless nickel plating method that is suitable for Mg-Gd-Y-Zr magnesium alloy for the first time; The existing electroless nickel plating method can continuously apply plating for 2 hours without peeling and bubbling, and can be plated entirely, with fast plating speed, good corrosion resistance of the coating, and strong bonding with the substrate; 2, the chemical nickel plating of the present invention adopts The main salt is basic nickel carbonate, which is less corrosive to the magnesium alloy substrate, simple to operate, good in plating solution stability, and easy to maintain; 3. The pretreatment method of the present invention has simple solution components, is easy to control, and has a stable process; 4. The zinc dipping layer obtained by the invented zinc dipping solution is uniform and has good binding force.

Description of drawings

Fig. 1 is the Mg-Gd-Y-Zr magnesium alloy electroless nickel plating process flowchart provided by the present invention;

Fig. 2 is the surface morphology of Mg-Gd-Y-Zr magnesium alloy after electroless nickel plating;

Figure 3 is a comparison diagram of the polarization curves of the Mg-Gd-Y-Zr magnesium alloy substrate and the nickel-plated layer.

Detailed ways

The present invention will be further described below in conjunction with examples, without limiting the present invention.

Example

The Mg-Gd-Y-Zr magnesium alloy electroless nickel plating method of the present invention will be described below in conjunction with the flow chart in FIG. 1 .

The experimental material is Mg-Gd-Y-Zr magnesium alloy, the alloy composition is (wt.%): Gd: 8-13%, Y: 2-6%, Zr: 0.3-0.8%, the rest is Mg and cannot be removed impurity elements. After extrusion and then aging, the heat treatment process is 220°C/2h. The size of the sample is a square sample of 18mm×10mm×3mm, which is processed according to the following steps:

Step 1: Grind the magnesium alloy with 180#, 360#, 1000#, 1500# sandpaper until the surface is clean without obvious impurities.

Step 2: immerse the polished magnesium alloy in a degreasing solution for degreasing.

The formula of degreasing solution is as follows: sodium carbonate 30g/L, sodium phosphate 30g/L and OP-102ml/L. The operating temperature is 75°C and the time is 1 min.

Step 3: Rinse the magnesium alloy with clean water for 30 seconds to remove the degreasing solution on the surface.

Step 4: Dip the magnesium alloy into the activation solution.

The activation solution formula is as follows: chromium oxalate 92g/L. The operating temperature is room temperature, and the processing time is 30s.

Step 5: Rinse the magnesium alloy with clean water for 30 seconds to remove the activation solution on the surface.

Step 6: Dip the magnesium alloy into the pickling solution.

The pickling solution formula is as follows: nitric acid 90ml/L and chromic acid 90g/L. The operating temperature is room temperature, and the processing time is 90s.

Step 7: Rinse the magnesium alloy with clean water for 30 seconds to remove the pickling solution on the surface.

Step eight: immerse the magnesium alloy in the activation solution for reactivation.

The activation solution formula is as follows: chromium oxalate 92g/L. The operating temperature is room temperature, and the processing time is 5s.

Step 9: Rinse the magnesium alloy with clean water for 30 seconds to remove the activation solution.

Step 10: Dip the magnesium alloy into a zinc dipping solution for zinc dipping treatment.

The formula of zinc dipping solution is as follows: zinc oxide 25g/L, hydroxyethylene diphosphoric acid 75ml/L, ethylenediamine 15ml/L and phosphoric acid 9ml/L. The operating temperature is 85°C, the pH value is 9.5, and the treatment time is 1min.

Step 11: Rinse the magnesium alloy with clean water for 30 seconds to remove the surface zinc solution.

Step 12: Dip the magnesium alloy into the plating solution for electroless nickel plating.

The formula of electroless nickel plating solution is as follows: basic nickel carbonate 15g/L; sodium hypophosphite 30g/L as reducing agent; hydrofluoric acid 45ml/L as corrosion inhibitor; lactic acid 33ml/L as complexing agent; sulfuric acid Cadmium 3mg/L and potassium iodate 6mg/L are used as brighteners. The operating temperature is 80-85°C, the pH value is 4.8, and the time is 2h.

Step 13: Rinse the plating solution on the surface of the nickel-plated magnesium alloy with clean water, and dry it at room temperature.

Step fourteen: immerse the nickel-plated magnesium alloy in a passivation solution for passivation treatment.

The passivation solution formula is as follows: road anhydride 50g/L. The operating temperature is 82-85°C, and the time is 5 minutes.

Step 15: Rinse the passivation solution on the surface of the magnesium alloy with clean water, and dry it at room temperature.

The nickel-plated layer of the Mg-Gd-Y-Zr magnesium alloy nickel-plated parts obtained by the above-mentioned process has been tested, and the performance is shown in the attached table:

Attached table: Adopt the performance of electroless nickel plating layer that the inventive method obtains

Fig. 2 is the coating morphology of Mg-Gd-Y-Zr magnesium alloy after electroless nickel plating. It can be seen from the figure that the coatings are uniform and fine cells, dense and without obvious defects. Figure 3 is a comparison diagram of the polarization curves of the Mg-Gd-Y-Zr magnesium alloy substrate and the nickel-plated layer. It can be seen from the figure that the self-corrosion potential of the substrate is about -1.325V, and the self-corrosion potential of the nickel-plated layer is about -0.251V. It can be seen that the corrosion resistance of the nickel plating layer is significantly improved compared with that of the substrate, the potential is positively shifted, and the current density is reduced by an order of magnitude.

Claims (5)

1. a Mg-Gd-Y-Zr magnesium alloy electroless nickel plating method is characterized in that, comprises the following steps: A. Pretreatment before plating First degreasing, activating, pickling, reactivating and galvanizing the magnesium alloy substrate; the degreasing solution is sodium carbonate 30g/L, sodium phosphate 30g/L and OP-101-2ml/L, and the operating temperature of the solution is 60- 80 ℃, processing time 1min; activation solution is chromium oxalate 92g/L, operating temperature is room temperature, processing time is 30s; pickling solution is nitric acid 90ml/L and chromic acid 90g/L, solution operating temperature is room temperature, processing time is 90-150s; the reactivation solution is chromium oxalate 92g/L, the operating temperature is room temperature, and the treatment time is 5-10s; the zinc immersion solution is zinc oxide 20-30g/L, hydroxyethylene diphosphate 70-80ml/L 7Diamine 12-18ml/L and phosphoric acid 8-10ml/L; the operating temperature is 82-86°C, the pH value is 9.2-9.6, and the treatment time is 1min; B. Conduct electroless nickel plating and passivation treatment. The nickel plating solution uses basic nickel carbonate as the main salt, sodium hypophosphite as the reducing agent, lactic acid as the complexing agent, hydrofluoric acid as the corrosion inhibitor, cadmium sulfate and iodic acid Potassium is a brightener, and finally passivated. 2. the Mg-Gd-Y-Zr magnesium alloy electroless nickel plating method according to claim 1 is characterized in that: the nickel plating solution consists of basic nickel carbonate 12-18g/L, sodium hypophosphite 25-35g/L L, hydrofluoric acid 40-50ml/L, lactic acid 28-35ml/L, brightener 3.5-5ml/L, nickel plating solution operating temperature 82-86°C, pH value 4.5-5.0, treatment time 2h. 3. Mg-Gd-Y-Zr magnesium alloy electroless nickel plating method according to claim 1, is characterized in that: described brightener is by 2-3mg/L cadmium sulfate and 5.5-7.5mg/L iodic acid Potassium composition. 4. The Mg-Gd-Y-Zr magnesium alloy electroless nickel plating method according to claim 1, characterized in that: the passivation solution is composed of chromic anhydride 50g/L, the operating temperature is 82-86°C, and the treatment time is 5min. 5. Mg-Gd-Y-Zr magnesium alloy electroless nickel plating method according to claim 1, is characterized in that: all carry out between each step of degreasing, activation, pickling, reactivation, zinc dipping and electroless nickel plating Rinse with water for 30s.

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