Process for rack plating of hard silver on aluminum alloy bar

Abstract

The invention discloses a process for rack plating of hard silver on an aluminum alloy bar. The process comprises the following steps: carrying out alkaline etching on a silver-plated surface of the aluminum alloy bar; the aluminum alloy bar subjected to alkali corrosion is subjected to primary acid etching treatment; carrying out primary zinc immersion treatment on the aluminum alloy bar subjected to the primary acid etching treatment; carrying out secondary acid etching treatment on the aluminum alloy bar subjected to zinc immersion treatment; carrying out secondary zinc immersion treatment on the zinc immersion treatment after the secondary acid etching treatment; copper pre-plating treatment is carried out on the zinc dipping treatment after the secondary zinc dipping treatment; pre-plating silver on the zinc-dipped pre-plated copper surface; and silver plating is carried out on the basis of pre-silver plating. The surface of the aluminum alloy is activated by adopting a method of secondary acid etching and zinc immersion after alkaline etching, so that metal deposition is facilitated, and the binding force between plating layers is improved; a plating layer is deposited on the surface of the aluminum alloy by adopting a method of pre-plating copper, pre-plating silver for bottoming and then plating silver, the speed of surface metal replacement reaction is controlled, and good binding force of the plating layer is ensured; and the thickness and the hardness of the plated layer of the silver-plated aluminum alloy bar meet the requirements of use conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of silver plating on aluminum alloys, and more specifically, to a process for rack plating hard silver on aluminum alloy bars. Background Art

[0002] Aluminum alloys have a low density, good corrosion resistance, high fatigue resistance, relatively high specific strength and specific stiffness, comparable to structural steel or even ultra-high strength steel. Therefore, they are widely used in the substation industry to reduce the structural weight after the overall assembly of the substation and improve the carrying capacity and speed.

[0003] However, plating on aluminum alloys is much more difficult and complex than on metal materials such as steel and copper. Due to its active nature, its surface easily reacts with oxygen in the air to form an oxide film, which hinders further surface treatment of the aluminum alloy. At the same time, the electrode potential of aluminum is very negative, and when immersed in the plating solution, it can undergo displacement reactions with various metal ions to form a contact coating on the aluminum, reducing the bonding strength between the coating and the aluminum substrate.

[0004] For example, the material of the conductive rod, which is the carrier for voltage conversion and current transmission in the substation, is aluminum alloy. As the conversion carrier, silver plating is required on all contact and connection surfaces to reduce resistance and increase conductivity. When the conductive rod is used as a moving or static contact seat, after surface silver plating, the conductivity can be greatly improved, the electrical contact impedance can be reduced, and at the same time, the antioxidant and corrosion resistance are significantly improved, extending the service life of the conductive rod. However, due to the length of the conductive rod being mostly between 3 meters and 10 meters, the current process is difficult to silver plate on the aluminum alloy surface and it is difficult to meet the requirements of the actual production process. Summary of the Invention

[0005] The purpose of the present invention is to provide a process for rack plating hard silver on aluminum alloy bars.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A process for rack plating hard silver on aluminum alloy bars, the process comprising the following steps: S1. Fix the aluminum alloy bar on the rack, coat the non-plated surface of the aluminum alloy bar with glue for shielding, and clean the surface of the aluminum alloy bar to be silver plated; S2. Perform alkaline etching on the silver-plated surface of the aluminum alloy bar; S3. Perform a first acid etching treatment on the aluminum alloy bar after alkaline corrosion; S4. Perform a first zinc immersion treatment on the aluminum alloy bar after the first acid etching treatment; S5. Perform a second acid etching treatment on the aluminum alloy bar after zinc immersion treatment; S6. Perform a second zinc immersion treatment on the zinc immersion treatment after the second acid etching treatment; S7. Perform a pre-copper plating treatment on the zinc immersion treatment after the second zinc immersion treatment; S8. Pre - plate silver on the surface of the copper - pre - plated surface after zinc immersion treatment; S9. Perform silver plating on the basis of pre - plated silver.

[0007] Preferably, the specific steps of alkaline etching in step S2 are as follows: Place the aluminum alloy rod in an aqueous solution containing 12 g / L - 18 g / L of sodium hydroxide, 45 g / L - 55 g / L of sodium carbonate, and 45 g / L - 55 g / L of trisodium phosphate. The solution temperature is 65°C ± 5, and the treatment time is 60 s - 80 s. After alkaline etching, the oxide and aluminum element can react quickly with strong alkali, achieving the effect of removing the oxide scale and roughening the surface of the substrate; however, other components such as copper, iron, magnesium, manganese, and silicon with relatively small contents are insoluble in alkali and remain on the surface of the conductive rod after alkaline etching to form "hanging ash", which must be removed by the subsequent acid - etching process.

[0008] Preferably, the specific steps of the secondary acid - etching treatment in step S3 and step S5 are as follows: Place the aluminum alloy rod in concentrated nitric acid prepared with 500 ml / L - 600 ml / L of nitric acid and 25 g / L - 60 g / L of ammonium bifluoride. The temperature is at room temperature, and the time is 20 s - 30 s. The acid - etching solution has strong acidity and strong oxidation properties, which can quickly dissolve the hanging ash on the surface of the conductive rod after alkaline etching, and at the same time form a very thin, uniform, and dense oxide film on the metal surface.

[0009] Preferably, the specific steps of the secondary zinc - immersion treatment in step S4 and step S6 are as follows: Place the aluminum alloy rod in an aqueous solution containing 190 g / L - 200 g / L of sodium hydroxide, 35 g / L - 45 g / L of zinc oxide, 100 g / L - 140 g / L of potassium sodium tartrate, 2 g / L - 4 g / L of ferric chloride, 1 g / L - 3 g / L of sodium sulfate, 15 g / L - 20 g / L of nickel sulfate, and 5 g / L - 6 g / L of sodium cyanide. The solution temperature is 20°C - 40°C, and the treatment time is 30 s - 60 s. The thin passivation film formed on the surface of the aluminum alloy rod dissolves in the zinc - immersion solution. After dissolution, the exposed metallic aluminum immediately undergoes a displacement reaction with zinc and iron ions. When the extremely thin zinc - iron displacement layer completely covers the surface, the reaction stops. Prolonged immersion often causes over - corrosion on the surface of the conductive rod, resulting in a loose and rough zinc layer. The two zinc - immersion solutions are the same, but the secondary zinc - immersion time is not longer than the primary zinc - immersion time. The primary zinc - immersion time can be appropriately increased as the temperature decreases to effectively ensure the deposition quality of zinc on the surface of the aluminum alloy.

[0010] Preferably, the specific steps of the pre-copper plating treatment in step S7 are: placing the aluminum alloy rod in a pure water solution containing 35g / L~42g / L of cuprous cyanide, 55g / L~65g / L of sodium cyanide, 50g / L~55g / L of potassium sodium tartrate, and 30g / L~35g / L of sodium carbonate, the solution temperature is 18°C~22°C, the treatment time is 3min~5min, the cyanide copper plating layer has good adhesion to the zinc layer and the subsequent silver plating layer, and has good ductility, electrical conductivity and thermal conductivity. The aluminum alloy rod is charged into the tank, and is electroplated with 2~2.5 times the current for 30S and then electroplated with normal current to ensure that the workpiece is plated as a whole.

[0011] Preferably, the specific steps of pre-silver plating in step S8 are: placing the aluminum alloy rod in a pure water solution containing 4g / L~6g / L of silver nitrate and 80g / L~90g / L of potassium cyanide, the solution temperature is 18°C~22°C, the electroplating current density is 0.5A / dm2~2A / dm2, and the time is 15s~30s.

[0012] Preferably, the specific steps of silver plating in step S9 are: placing the aluminum alloy rod in a pure water solution containing 35g / L~45g / L silver nitrate, 110g / L~140g / L potassium cyanide, 8g / L~10g / L potassium carbonate, 18g / L~20g / L potassium sodium tartrate, and 8ml / L~10ml / L brightener, the solution temperature is 18°C~22°C, and the electroplating current density is 0.6A / dm2~1.2A / dm2.

[0013] Preferably, the electroplating solution in step S8 is composed of low main salt and high complex, which effectively reduces the replacement reaction rate on the one hand; on the other hand, the plating solution has a high degree of complexation, greatly improving the cathode polarization, thereby obtaining a transition layer with fine crystals and good bonding strength.

[0014] Preferably, in the electroplating process in step S9, a 99.99% pure silver plate is used as the anode. Under the action of the power supply, the anode loses electrons to generate silver ions that dissolve in the plating solution; the silver ions obtain electrons at the cathode (aluminum alloy rod) to generate silver element, which is deposited on the surface of the aluminum alloy rod.

[0015] Compared with the prior art, the advantages of the present invention are: The present invention activates the surface of the aluminum alloy by adopting a method of secondary acid etching followed by zinc immersion, thereby facilitating metal deposition and improving the bonding strength between the coatings. The coating is deposited on the surface of the aluminum alloy by pre-copper plating and pre-silver plating followed by silver plating. The speed of the surface metal replacement reaction is controlled to ensure good coating adhesion. The thickness and hardness of the coating on the aluminum alloy bar after silver plating meet the requirements of the use conditions, and the conductive, corrosion-resistant and antioxidant properties are excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or in the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is a flowchart of a process for hanging and electroplating hard silver on an aluminum alloy bar of the present invention. Specific embodiments

[0018] The following will elaborate on the preferred embodiments of the present invention in conjunction with the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0019] Refer to Figure 1 As shown, the present invention provides a process for hanging and electroplating hard silver on an aluminum alloy bar, and the process includes the following steps: S1. Place the aluminum alloy bar on the rack and fix it. Glue the non-plated surface of the aluminum alloy bar for shielding, and clean the surface of the aluminum alloy bar to be electroplated with silver. S2. Perform alkaline etching on the silver-plated surface of the aluminum alloy bar. S3. Perform a first acid etching treatment on the aluminum alloy bar after alkaline corrosion. S4. Perform a first zinc immersion treatment on the aluminum alloy bar after the first acid etching treatment. S5. Perform a second acid etching treatment on the aluminum alloy bar after zinc immersion treatment. S6. Perform a second zinc immersion treatment on the zinc immersion treatment after the second acid etching treatment. S7. Perform a pre-copper plating treatment on the zinc immersion treatment after the second zinc immersion treatment. S8. Pre-plate silver on the surface of the zinc immersion treatment pre-coated with copper. S9. Perform silver plating on the basis of pre-plated silver. Embodiment

[0020] Take 6 φ90 aluminum bar samples. Machine the two flat surfaces of the aluminum bar samples, and place the aluminum bar samples in an aqueous solution containing 15 g / L of sodium hydroxide, 50 g / L of sodium carbonate, and 50 g / L of trisodium phosphate, at a temperature of 62 °C for 30 s. After the above treatment, place the aluminum bar samples in concentrated nitric acid prepared with 650 ml / L of nitric acid and 28 g / L of ammonium bifluoride, at room temperature for 20 s. After the above treatment, the aluminum rod sample is placed in an aqueous solution containing 200 g / L of sodium hydroxide, 40 g / L of zinc oxide, 110 g / L of potassium sodium tartrate, 2.5 g / L of ferric chloride, 2 g / L of sodium sulfate, 15 g / L of nickel sulfate, and 5.5 g / L of sodium cyanide. The temperature is 22 °C and the time is 30 s; After the above treatment, the aluminum rod sample is placed in concentrated nitric acid prepared with 650 ml / L of nitric acid and 28 g / L of ammonium bifluoride. The temperature is room temperature and the time is 20 s; After the above treatment, the aluminum rod sample is placed in an aqueous solution containing 200 g / L of sodium hydroxide, 40 g / L of zinc oxide, 110 g / L of potassium sodium tartrate, 2.5 g / L of ferric chloride, 2 g / L of sodium sulfate, 15 g / L of nickel sulfate, and 5.5 g / L of sodium cyanide. The temperature is 22 °C and the time is 20 s; After the above treatment, the aluminum rod sample is placed in a pure aqueous solution containing 40 g / L of cuprous cyanide, 60 g / L of sodium cyanide, 50 g / L of potassium sodium tartrate, and 30 g / L of sodium carbonate. The temperature is 22 °C and the time is 3 min; After the above treatment, the aluminum rod sample is placed in a pure aqueous solution containing 5 g / L of silver nitrate and 85 g / L of potassium cyanide. The temperature is 20 °C, the current density is 1 A / dm2, and the time is 15 s; After the above treatment, the aluminum rod sample is placed in a pure aqueous solution containing 40 g / L of silver nitrate, 120 g / L of potassium cyanide, 8 g / L of potassium carbonate, 18 g / L of potassium sodium tartrate, and 8 ml / L of brightener. The temperature is 20 °C, the current density is 0.6 A / dm2, and the time is 22 min.

[0021] After the above treatment of the aluminum rod sample, the inspection is carried out according to the requirements of the HB / Z5074 silver plating process. By visual inspection, the silver plating layer on the aluminum alloy is silver-white, the coating is delicate, flat, and firmly bonded. After heating to 130 °C for one hour by the thermal shock method and then cooling to room temperature, no bubbles are observed under an 8-fold magnifying glass. The coating thickness is measured to be 14 μm using a handheld spectrometer. According to the method specified in GB / T9790, the Vickers hardness is measured to be 150 HV. For the discoloration requirement, the silver-plated surface is immersed in a 5% potassium sulfide solution for more than 5 min, and the surface of the silver plating layer does not change color, and it is judged to be qualified. Example

[0022] 12 φ90 aluminum rod conductors are placed on the rack. The silver-plated surface is φ90, and the length of the cylindrical side is 170 mm. The side plane is machined, rubberized, and placed on the rack; The above conductors are placed in an aqueous solution containing 20 g / L of sodium hydroxide, 50 g / L of sodium carbonate, and 50 g / L of trisodium phosphate. The temperature is 65 °C and the time is 40 s; The conductors after the above treatment are placed in concentrated nitric acid prepared with 650 ml / L of nitric acid and 25 g / L of ammonium bifluoride. The temperature is room temperature and the time is 25 s; The conductive rod after the above treatment is placed in an aqueous solution containing 220 g / L of sodium hydroxide, 40 g / L of zinc oxide, 100 g / L of potassium sodium tartrate, 2.5 g / L of ferric chloride, 2 g / L of sodium sulfate, 15 g / L of nickel sulfate, and 5.5 g / L of sodium cyanide, at a temperature of 25 °C for 50 s; The conductive rod after the above treatment is placed in concentrated nitric acid prepared with 650 ml / L of nitric acid and 25 g / L of ammonium bifluoride, at room temperature for 20 s; The conductive rod after the above treatment is placed in an aqueous solution containing 220 g / L of sodium hydroxide, 40 g / L of zinc oxide, 100 g / L of potassium sodium tartrate, 2.5 g / L of ferric chloride, 2 g / L of sodium sulfate, 15 g / L of nickel sulfate, and 5.5 g / L of sodium cyanide, at a temperature of 25 °C for 25 s; The conductive rod after the above treatment is placed in a pure aqueous solution containing 42 g / L of cuprous cyanide, 60 g / L of sodium cyanide, 50 g / L of potassium sodium tartrate, and 30 g / L of sodium carbonate, at a temperature of 25 °C for 5 min; The conductive rod after the above treatment is placed in a pure aqueous solution containing 5 g / L of silver nitrate and 85 g / L of potassium cyanide, at a temperature of 22 °C, with a current density of 0.8 A / dm2 for 22 s; The conductive rod after the above treatment is placed in a pure aqueous solution containing 45 g / L of silver nitrate, 115 g / L of potassium cyanide, 8 g / L of potassium carbonate, 18 g / L of potassium sodium tartrate, and 10 ml / L of brightener, at a temperature of 22 °C, with a current density of 0.8 A / dm2.

[0023] After the conductive rod has undergone the above treatment, in accordance with the requirements of the HB / Z5074 silver plating process for aluminum alloy, upon visual inspection, the silver plating layer is silver-white, with a fine, smooth, and firmly bonded coating. After heating to 130 °C for one hour using the thermal shock method and then cooling to room temperature, no blisters are observed under an 8-fold magnifying glass. The resistance of the conductive rod is measured using a resistance tester to be less than 25 micro-ohms. The coating thickness is measured using a general handheld spectrometer to be 12 μm. In accordance with the method specified in GB / T9790, the Vickers hardness is measured to be 138 HV. For the discoloration requirement, the silver-plated surface is immersed in a 5% potassium sulfide solution for more than 5 min, and if the silver plating layer does not change color, it is judged to be qualified, meeting the requirements for thickness, hardness, and conductivity.

[0024] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, the patent owner can make various deformations or modifications within the scope of the appended claims. As long as it does not exceed the protection scope described by the claims of the present invention, it should be within the protection scope of the present invention.

Claims

1. A process for barrel plating hard silver on an aluminum alloy bar, characterized in that, The process includes the following steps: S1. Fix the aluminum alloy bar on the rack, apply glue masking on the non-plated surface of the aluminum alloy bar, and clean the surface of the aluminum alloy bar to be silver-plated. S2. Perform alkaline etching on the silver-plated surface of the aluminum alloy bar. S3. Conduct a first acid etching treatment on the aluminum alloy bar after alkaline corrosion. S4. Conduct a first zinc immersion treatment on the aluminum alloy bar after the first acid etching treatment. S5. Perform a second acid etching treatment on the aluminum alloy bar after zinc immersion treatment. S6. Conduct a second zinc immersion treatment on the aluminum alloy bar after the second acid etching treatment. S7. Perform a pre-copper plating treatment on the aluminum alloy bar after the second zinc immersion treatment. S8. Pre-plate silver on the surface of the pre-copper plated zinc immersion treatment. S9. Perform silver plating on the basis of pre-plated silver.

2. The process for barrel plating hard silver on an aluminum alloy bar according to claim 1, characterized in that, The specific steps of alkaline etching in step S2 are as follows: Place the aluminum alloy bar in an aqueous solution containing 12 g / L - 18 g / L of sodium hydroxide, 45 g / L - 55 g / L of sodium carbonate, and 45 g / L - 55 g / L of trisodium phosphate. The solution temperature is 65°C ± 5, and the treatment time is 60 s - 80 s.

3. The process for hanging plating hard silver on an aluminum alloy bar according to claim 1, characterized in that, The specific steps of the second acid etching treatment in steps S3 and S5 are as follows: Place the aluminum alloy bar in concentrated nitric acid configured with 500 ml / L - 600 ml / L of nitric acid and 25 g / L - 60 g / L of ammonium bifluoride. The temperature is at room temperature, and the time is 20 s - 30 s.

4. The process for hanging plating hard silver on an aluminum alloy bar according to claim 1, characterized in that, The specific steps of the second zinc immersion treatment in steps S4 and S6 are as follows: Place the aluminum alloy bar in an aqueous solution containing 190 g / L - 200 g / L of sodium hydroxide, 35 g / L - 45 g / L of zinc oxide, 100 g / L - 140 g / L of potassium sodium tartrate, 2 g / L - 4 g / L of ferric chloride, 1 g / L - 3 g / L of sodium sulfate, 15 g / L - 20 g / L of nickel sulfate, and 5 g / L - 6 g / L of sodium cyanide. The solution temperature is 20°C - 40°C, and the treatment time is 30 s - 60 s.

5. A process for hanging plating hard silver on an aluminum alloy bar according to claim 1, characterized in that, The specific steps of the pre-copper plating treatment in step S7 are as follows: Place the aluminum alloy bar in a pure aqueous solution containing 35 g / L - 42 g / L of cuprous cyanide, 55 g / L - 65 g / L of sodium cyanide, 50 g / L - 55 g / L of potassium sodium tartrate, and 30 g / L - 35 g / L of sodium carbonate. The solution temperature is 18°C - 22°C, and the treatment time is 3 min - 5 min.

6. A process for hanging plating hard silver on an aluminum alloy bar according to claim 1, characterized in that, The specific steps of pre-plating silver in step S8 are as follows: Place the aluminum alloy bar in a pure aqueous solution containing 4 g / L - 6 g / L of silver nitrate and 80 g / L - 90 g / L of potassium cyanide. The solution temperature is 18°C - 22°C, the current density of electroplating is 0.5 A / dm2 - 2 A / dm2, and the time is 15 s - 30 s.

7. A process for hanging plating hard silver on an aluminum alloy bar according to claim 1, characterized in that, The specific steps of silver plating in step S9 are as follows: Place the aluminum alloy bar in a pure aqueous solution containing 35 g / L - 45 g / L of silver nitrate, 110 g / L - 140 g / L of potassium cyanide, 8 g / L - 10 g / L of potassium carbonate, 18 g / L - 20 g / L of potassium sodium tartrate, and 8 ml / L - 10 ml / L of brightening agent. The solution temperature is 18°C - 22°C, and the current density of electroplating is 0.6 A / dm2 - 1.2 A / dm2.

8. A process for hanging and plating hard silver on an aluminum alloy bar according to claim 6, characterized in that: The electroplating solution in step S8 is composed of a low main salt and a high complexing agent.

9. A process for hanging plating hard silver on an aluminum alloy bar according to claim 7, characterized in that: In the electroplating process of step S9, a 99.99% pure silver plate is used as the anode.

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