Aluminum and aluminum alloy plating is more difficult, because aluminum has a strong affinity for oxygen, the surface is easily oxidized; aluminum is amphoteric metal, is not stable in acid, alkali; aluminum potential is very negative, easy to be immersed in the plating solution Erosion and displacement of the metal being plated; Aluminum's expansion coefficient is larger than most metals, so the coating is easy to air bubbles, fall off, affecting the binding force. The key to the electroplating of aluminum and aluminum alloys is the special pre-plating treatment that removes the natural oxide film and prevents its re-formation, as well as preventing the displacement reaction when the aluminum parts are immersed in the electrolyte. As a naval overhauled aircraft factory, we often encounter aluminum and aluminum alloy plating during the repair process. Through the experiment, the better process conditions were explored. The surface of the aluminum alloy plating blessing parts not only has a good gloss, but also has good bonding and corrosion resistance and meets the requirements for navigation marks. This article describes the plating process for the repair of old aluminum alloy parts.
1 process flow
In addition to oil (degreasing) to remove the old coating one or two cleaning an alkali etching one or two cleaning a gray descaling (light) one or two cleaning once a sink zinc one or two cleaning a zinc removal layer one or two Cleaning a secondary zinc-sulfuric acid neutralization, activation and cleaning of a chemical nickel electroplating one or two cleaning an active one rhodium plating one or two cleaning a passivation one or two cleaning blow dry one aging one test storage
2 main process description
2.1 Degreasing liquid composition and process conditions
Sodium hydroxide 40 - 609/L, 70 - 90 "c, 1 - Zmin. Severe oils are first cleaned with organic solvents.
2.2 Retire old plating
The removal of the old coating is one of the key processes for the tinning of aluminum alloys.
2.2.1 Retirement of old fortified layer solution composition and operating conditions
Leave 10 to 150 L of nitrate for room temperature. Retire.
2.2.2 Retire old zinc layer solution composition and operating conditions
Sulfuric acid 10 to 150 stay L, at room temperature, retired so far.
2.2.3 Retirement of old oxide film solution composition and operating conditions
Sodium hydroxide 40-609/L, 50-90 "C, retired.
2.24 Retreat of Ni-P alloy solution composition and process conditions
Concentrated nitric acid 700 mL/L, sodium chloride 30 to 409/L, hexamethylenetetramine 6 to 109/L, urea 15 to ZoglL, room temperature.
(1) The pre-plating articles should be dried or blown with cold air to prevent the water content from reducing the concentration of nitric acid, resulting in corrosion of the substrate.
(2) The deplated parts should be cleaned quickly so as not to produce a black oxide film on the surface after the deplating. Aluminum alloy electroless nickel plating is generally used to remove concentrated nitric acid. Although concentrated nitric acid has strong oxidizing ability, concentrated nitric acid has a slower corrosion rate to the Ni-P alloy layer, and a large amount of No 2 gas is generated when the concentrated nitric acid is removed, which greatly pollutes the environment. After the electroless Ni-P alloy layer of precision parts is deplated, the amount of concentrated nitric acid on the base metal is often excessive, especially for bolts. In order to overcome the drawbacks of the over-etching of the electroless nickel plating layer on the bolts, we have passed hundreds of tests to screen out the above-mentioned nickel removal process. When the Ni-P alloy layer is withdrawn, the corrosion of the substrate is very small, and it is not easy to be over-etched, and the gas during the deposition is also less, the quality of the plating can be guaranteed, and the working environment is improved.
2.3 Alkaline erosion
Sodium hydroxide 40-6og/L, 70-90 "c, 1- 2 and n.
2.4 To remove dirt (light out
After the surface of aluminum and aluminum alloys are alkali-etched, a layer of grey or black ash is attached to the surface of the parts, and is also not cleaned in flowing cold or hot water, and can be removed in the following solutions. Chromium drunk 109, sulphuric acid 10mIJL, room temperature, except net. The ash on the surface of aluminum alloy products containing silicon or manganese (especially cast aluminum with higher silicon content) should be removed in the following solution: V (nitric acid): V (hydrofluoric acid) 2:1 mixed acid (Because the reaction is fierce, add a certain amount of corrosion inhibitor), dip 55 or so, can be removed.
2.5 leaching zinc [,
Dipping zinc solution formula and process conditions: sodium hydroxide 40 to 509/L, zinc oxide 10 to 150 stay L, potassium sodium tartrate 11 to 20 years old L, ferric chloride 1-29, hydrofluoric acid lg/L, Room temperature, (30 ± 5) 5. Zinc leaching is a very critical process, and a good zinc immersion layer can be well combined with the base and the subsequent nickel layer, and can mask defects on the surface of the substrate and help to obtain a good coating.
We use alkaline zinc dipping solution. It is only necessary to dip a layer of zinc on the surface of the workpiece to allow the difference in color. However, it must be ensured that the surface of the substrate is completely impregnated with a zinc layer. Otherwise, the next step cannot be performed. After immersing zinc, do not rinse with water.
2.6 zinc removal
When zinc is first immersed, the aluminum oxide film is first dissolved, zinc is deposited on the surface of the aluminum workpiece, and it is inevitable that there is still a small amount of oxide film remaining, the deposition layer is not uniform, and the bonding force is poor. After the nitric acid was removed, the surface of the aluminum workpiece was further purified. The zinc is then submerged for a second time in the zinc dipping solution to obtain a dense, uniform and strong zinc layer. The composition and operating conditions of zinc stripping solution: nitric acid somuL with a mass fraction of 65%, normal temperature, (5 ± 5) 5, and the zinc layer must be completely removed.
2.7 Neutralization and Activation
Solution composition and process conditions: sulfuric acid 0.7 to 1.09/L, room temperature, 5 to 10,.
2. 8 electroless nickel plating [, · 2] is different from the general electroplating electroless nickel plating is carried out by the surface of the autocatalytic reaction; and these are based on proper pretreatment conditions, the pretreatment is not good will make the coating Poor bonding, rough, corrosion resistance, etc. In addition, the electroless nickel plating solution is more sensitive, and the residual solution and residue brought into the pretreatment will affect the life of the plating solution, resulting in deterioration of the plating solution. Plating solution formulation and process conditions: Niso4·7 practice 0219/L, Na from poZ·practice 0249/L, lactic acid (88%) 3omIJL, CZ profile C00HZg/L, lead ion 1 ad/L, pH value 4.5±0.5 The temperature is (95 soil 2). C, (24 ± 8) and n, the deposition rate is 17%, and the mass fraction of phosphorus in the coating is 8% to 9%. In the process of electroless nickel plating, the surface of the electroless nickel plating layer allows the nickel layer to be black, but no color difference is allowed and the color is required to be uniform.
2.9 tin plating
Plating bath composition and process conditions: Cd040-459/L, NaCNllO-1409/L, N-N 5 Chou '10-040-609/L, NIS04- 7 from 00.5-1.59/L, brightener 5-smL/L, 15-30OC, 1.0-2.SA/dmZ, 3-6v, 15-60min, anode materials Cd-1, Cd-2.
2.9.1 Commutation Plating
(1) After electroplating smin, commutation plating is allowed, tK: gas = 10:1.
(2) At the beginning, give a small current, gradually rise to normal current within 1 to 5 and n; 1 to 3 minutes before the slot, sometimes to increase the current density of 0.5 to 1.0 times to avoid pinhole and bubble phenomenon Impact plating.
3 detection
According to the aerospace industry standard aviation industry standard HB5036: 92 inspection side.
3.1 Appearance
The visual inspection is carried out with natural scattered light or white transmitted light. In special cases, a 3- to 5-fold magnifying glass is used for inspection. The passivated tantalum coating is gold-yellow with a rainbow, and the passivation film is complete and uniform in color.
3.2 Thickness
The thickness of the fortified layer is 15-25 m.
3.3 Cohesion
The size of 7Ommx25mm fire (1 - 2) mm, the surface roughness of the magic sample, clamped with pliers, repeated bending 180 "(curved to each side 90) until the fracture; or the part (sample) bending 180. Until the part (specimen) fractures, the coating should not be separated from the base metal. When examined with a 5x magnifier, cracks occur in the base metal or plating, but no peeling or peeling, the coating adhesion is acceptable. Test aluminum alloy plating parts with good adhesion.
3.4 Corrosion resistance
The rhodium plating layer is subjected to a salt spray corrosion test according to GB6458, and the corrosion resistance reaches the HB5362 requirement. The time for the white corrosion product of the tin-plating yellow passivation salt spray test was greater than %h; the time for the red corrosion product to appear in the salt spray test was greater than 360 hours.
3.5 Hardness
The Vickers hardness of the coating is 475, which is higher than the hardness of the aluminum alloy by 120.
4 Conclusion
With the development of miniaturization and high motorization of military equipment in China, more and more aluminum alloy materials are used in airborne equipment products. Through trials and investigations, a complete set of aluminum and aluminum alloy rhodium-plating repair process was explored. The product quality fully met the requirements of the military and was well received by the users. In particular, there has been a new breakthrough in the nickel-removal process. The process is characterized by small pollution, low gas, and good over-corrosion protection, and plays an important role in the repair of aluminum and aluminum alloy parts on aircraft.
1 process flow
In addition to oil (degreasing) to remove the old coating one or two cleaning an alkali etching one or two cleaning a gray descaling (light) one or two cleaning once a sink zinc one or two cleaning a zinc removal layer one or two Cleaning a secondary zinc-sulfuric acid neutralization, activation and cleaning of a chemical nickel electroplating one or two cleaning an active one rhodium plating one or two cleaning a passivation one or two cleaning blow dry one aging one test storage
2 main process description
2.1 Degreasing liquid composition and process conditions
Sodium hydroxide 40 - 609/L, 70 - 90 "c, 1 - Zmin. Severe oils are first cleaned with organic solvents.
2.2 Retire old plating
The removal of the old coating is one of the key processes for the tinning of aluminum alloys.
2.2.1 Retirement of old fortified layer solution composition and operating conditions
Leave 10 to 150 L of nitrate for room temperature. Retire.
2.2.2 Retire old zinc layer solution composition and operating conditions
Sulfuric acid 10 to 150 stay L, at room temperature, retired so far.
2.2.3 Retirement of old oxide film solution composition and operating conditions
Sodium hydroxide 40-609/L, 50-90 "C, retired.
2.24 Retreat of Ni-P alloy solution composition and process conditions
Concentrated nitric acid 700 mL/L, sodium chloride 30 to 409/L, hexamethylenetetramine 6 to 109/L, urea 15 to ZoglL, room temperature.
(1) The pre-plating articles should be dried or blown with cold air to prevent the water content from reducing the concentration of nitric acid, resulting in corrosion of the substrate.
(2) The deplated parts should be cleaned quickly so as not to produce a black oxide film on the surface after the deplating. Aluminum alloy electroless nickel plating is generally used to remove concentrated nitric acid. Although concentrated nitric acid has strong oxidizing ability, concentrated nitric acid has a slower corrosion rate to the Ni-P alloy layer, and a large amount of No 2 gas is generated when the concentrated nitric acid is removed, which greatly pollutes the environment. After the electroless Ni-P alloy layer of precision parts is deplated, the amount of concentrated nitric acid on the base metal is often excessive, especially for bolts. In order to overcome the drawbacks of the over-etching of the electroless nickel plating layer on the bolts, we have passed hundreds of tests to screen out the above-mentioned nickel removal process. When the Ni-P alloy layer is withdrawn, the corrosion of the substrate is very small, and it is not easy to be over-etched, and the gas during the deposition is also less, the quality of the plating can be guaranteed, and the working environment is improved.
2.3 Alkaline erosion
Sodium hydroxide 40-6og/L, 70-90 "c, 1- 2 and n.
2.4 To remove dirt (light out
After the surface of aluminum and aluminum alloys are alkali-etched, a layer of grey or black ash is attached to the surface of the parts, and is also not cleaned in flowing cold or hot water, and can be removed in the following solutions. Chromium drunk 109, sulphuric acid 10mIJL, room temperature, except net. The ash on the surface of aluminum alloy products containing silicon or manganese (especially cast aluminum with higher silicon content) should be removed in the following solution: V (nitric acid): V (hydrofluoric acid) 2:1 mixed acid (Because the reaction is fierce, add a certain amount of corrosion inhibitor), dip 55 or so, can be removed.
2.5 leaching zinc [,
Dipping zinc solution formula and process conditions: sodium hydroxide 40 to 509/L, zinc oxide 10 to 150 stay L, potassium sodium tartrate 11 to 20 years old L, ferric chloride 1-29, hydrofluoric acid lg/L, Room temperature, (30 ± 5) 5. Zinc leaching is a very critical process, and a good zinc immersion layer can be well combined with the base and the subsequent nickel layer, and can mask defects on the surface of the substrate and help to obtain a good coating.
We use alkaline zinc dipping solution. It is only necessary to dip a layer of zinc on the surface of the workpiece to allow the difference in color. However, it must be ensured that the surface of the substrate is completely impregnated with a zinc layer. Otherwise, the next step cannot be performed. After immersing zinc, do not rinse with water.
2.6 zinc removal
When zinc is first immersed, the aluminum oxide film is first dissolved, zinc is deposited on the surface of the aluminum workpiece, and it is inevitable that there is still a small amount of oxide film remaining, the deposition layer is not uniform, and the bonding force is poor. After the nitric acid was removed, the surface of the aluminum workpiece was further purified. The zinc is then submerged for a second time in the zinc dipping solution to obtain a dense, uniform and strong zinc layer. The composition and operating conditions of zinc stripping solution: nitric acid somuL with a mass fraction of 65%, normal temperature, (5 ± 5) 5, and the zinc layer must be completely removed.
2.7 Neutralization and Activation
Solution composition and process conditions: sulfuric acid 0.7 to 1.09/L, room temperature, 5 to 10,.
2. 8 electroless nickel plating [, · 2] is different from the general electroplating electroless nickel plating is carried out by the surface of the autocatalytic reaction; and these are based on proper pretreatment conditions, the pretreatment is not good will make the coating Poor bonding, rough, corrosion resistance, etc. In addition, the electroless nickel plating solution is more sensitive, and the residual solution and residue brought into the pretreatment will affect the life of the plating solution, resulting in deterioration of the plating solution. Plating solution formulation and process conditions: Niso4·7 practice 0219/L, Na from poZ·practice 0249/L, lactic acid (88%) 3omIJL, CZ profile C00HZg/L, lead ion 1 ad/L, pH value 4.5±0.5 The temperature is (95 soil 2). C, (24 ± 8) and n, the deposition rate is 17%, and the mass fraction of phosphorus in the coating is 8% to 9%. In the process of electroless nickel plating, the surface of the electroless nickel plating layer allows the nickel layer to be black, but no color difference is allowed and the color is required to be uniform.
2.9 tin plating
Plating bath composition and process conditions: Cd040-459/L, NaCNllO-1409/L, N-N 5 Chou '10-040-609/L, NIS04- 7 from 00.5-1.59/L, brightener 5-smL/L, 15-30OC, 1.0-2.SA/dmZ, 3-6v, 15-60min, anode materials Cd-1, Cd-2.
2.9.1 Commutation Plating
(1) After electroplating smin, commutation plating is allowed, tK: gas = 10:1.
(2) At the beginning, give a small current, gradually rise to normal current within 1 to 5 and n; 1 to 3 minutes before the slot, sometimes to increase the current density of 0.5 to 1.0 times to avoid pinhole and bubble phenomenon Impact plating.
3 detection
According to the aerospace industry standard aviation industry standard HB5036: 92 inspection side.
3.1 Appearance
The visual inspection is carried out with natural scattered light or white transmitted light. In special cases, a 3- to 5-fold magnifying glass is used for inspection. The passivated tantalum coating is gold-yellow with a rainbow, and the passivation film is complete and uniform in color.
3.2 Thickness
The thickness of the fortified layer is 15-25 m.
3.3 Cohesion
The size of 7Ommx25mm fire (1 - 2) mm, the surface roughness of the magic sample, clamped with pliers, repeated bending 180 "(curved to each side 90) until the fracture; or the part (sample) bending 180. Until the part (specimen) fractures, the coating should not be separated from the base metal. When examined with a 5x magnifier, cracks occur in the base metal or plating, but no peeling or peeling, the coating adhesion is acceptable. Test aluminum alloy plating parts with good adhesion.
3.4 Corrosion resistance
The rhodium plating layer is subjected to a salt spray corrosion test according to GB6458, and the corrosion resistance reaches the HB5362 requirement. The time for the white corrosion product of the tin-plating yellow passivation salt spray test was greater than %h; the time for the red corrosion product to appear in the salt spray test was greater than 360 hours.
3.5 Hardness
The Vickers hardness of the coating is 475, which is higher than the hardness of the aluminum alloy by 120.
4 Conclusion
With the development of miniaturization and high motorization of military equipment in China, more and more aluminum alloy materials are used in airborne equipment products. Through trials and investigations, a complete set of aluminum and aluminum alloy rhodium-plating repair process was explored. The product quality fully met the requirements of the military and was well received by the users. In particular, there has been a new breakthrough in the nickel-removal process. The process is characterized by small pollution, low gas, and good over-corrosion protection, and plays an important role in the repair of aluminum and aluminum alloy parts on aircraft.
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