Surface treatment: after mechanical and chemical treatment, a protective layer can be formed on the surface of the product to protect the body. It can reach a stable state in nature, increase the corrosion resistance of the blank, increase the aesthetics of the product, and thus enhance the value of the product. The choice of surface treatment type should first start from the perspective of use environment, service life and artificial appreciation, and of course economic value is also the core of consideration.
The surface treatment process includes pretreatment, film formation and film post-treatment. Packaging and storage. Shipping and other processes, in which pretreatment includes mechanical treatment and chemical treatment.
Mechanical treatment includes sand blasting, shot blasting, grinding, polishing, waxing and other processes. The purpose of mechanical treatment is to eliminate the unevenness of the product surface and remedy other appearance defects on the surface. Chemical treatment can remove the oil stain and rust on the surface of the product, form a layer of industrial aluminum profile, make the film-forming substance better combine or blend into the active metal body, ensure the coating is in a stable state, and increase the binding force of the protective layer, thus achieving the role of protecting the body.
Surface treatment of aluminum material
Common chemical treatments of aluminum include chromium plating, painting, electroplating, anodic oxidation and electrophoresis. Among them, mechanical treatment includes drawing, polishing, spraying and grinding.
Aluminum profile system
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Section 1 Chromization
Chromizing will form a chemical conversion film on the surface of the product, and the thickness of the film is 0.5-4 μm m. This conversion film has good adsorption and is mainly used as coating primer. The appearance is golden yellow, aluminum, green and so on. This conversion film has good conductivity and is the best choice for electronic products, such as mobile phone batteries and conductive strips in magnetoelectric equipment. The film is suitable for all aluminum and aluminum alloy products. However, the conversion film is soft and not wear-resistant, which is not conducive to the use of external parts of the product.
Process flow of chromizing:
Degreasing-> dealumination->; Chromizing->; Packaging-> warehousing
Chromizing is suitable for aluminum and aluminum alloy, magnesium and magnesium alloy products.
Quality requirements:
1) The color should be uniform, and the film layer should be fine, and there should be no bumps, scratches, hand touches, roughness, ash dropping and other phenomena.
2) The film thickness is 0.3-4um.
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Section II, Anodizing
Anodizing: A uniform and compact oxide layer (Al2O3) can be formed on the product surface. The film can make the surface hardness of the product reach (200-300HV). If special products can be hard anodized, the surface hardness of products can reach 400- 1200HV, so hard anodizing is an indispensable surface treatment process for cylinders and transmissions.
In addition, the product has excellent wear resistance and can be used as a necessary process for aviation and aerospace related products. The difference between anodic oxidation and hard anodic oxidation: anodic oxidation can color the workbench, and its decoration is much better than hard oxidation. Key points of construction: Anodizing requires strict materials, and different materials have different decorative effects. Commonly used materials are 606 1, 6063, 7075, 2024, etc. Among them, the relative effect of 2024 is worse. Because of the different CU content in the material, 7075 is hard oxidized to yellow, 606 1, 6063 is yellow.
First, the common process
Common anodizing processes include matte, smooth, smooth dyeing and matte dyeing (which can be dyed in any color system). Polishing bright color, polishing matte color, polishing bright color dyeing, polishing matte color. Spray bright complexion, spray complexion, sand blasting dyeing. The above plating types can be used for lighting equipment.
Second, the anodic oxidation process
Deoiling->; Alkaline corrosion->; Chemical throwing-> neutralization-> Li Di-> neutralization
Anodizing->; Dyeing->; Hole sealing->; Hot water washing-> drying
Third, the common abnormal quality judgment
There is a spot on the surface. This abnormality is generally caused by poor quenching and tempering of metal or poor material itself, so treatment methods and re-heat treatment are adopted. Or a different material.
B has a rainbow color on its surface. This abnormality is usually caused by anode operation error. , loose when hanging, resulting in poor conductivity of the product. , treatment method, back to the anode treatment.
C, surface bumps, serious scratches. This abnormality is generally caused by careless operation during transportation or processing, and the treatment method is to return the electricity and re-polish it.
D, white spots appear on the surface during dyeing. This abnormality is usually caused by oil or other impurities in water during anode operation.
Fourth, quality standards.
The film thickness of 1) is 5-25um, the hardness is more than 200HV, and the color change rate of hole sealing experiment is less than 5%.
2) The salt spray test lasts for more than 36 hours, which can reach the CNS standard of grade 9 or above.
3) The appearance shall be free of bumps, scratches and colorful clouds. There should be no spots and yellowing on the surface.
4. Die-cast aluminum, such as A380, A365 and A382, cannot be anodized.
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Section III, Aluminum Plating Process
First, the advantages of aluminum and aluminum alloy materials
It has the advantages of good conductivity, fast heat transfer, light specific gravity and easy molding, but aluminum and aluminum alloys have the disadvantages of low hardness, non-wear resistance, easy intergranular corrosion and difficult welding, which affect the application scope. Therefore, in modern industry, electroplating is used to solve this problem in order to foster strengths and avoid weaknesses.
Second, the advantages of electroplating aluminum
1) Improve the decoration,
2) improve the surface hardness and wear resistance.
3) Reduce friction coefficient and improve lubricity.
4) improve the surface conductivity.
5) Improve corrosion resistance (including combination with other metals)
6) Easy to weld
7) Improve the bonding force with rubber during hot pressing.
8) Improve the reflectivity.
9) Repair dimensional tolerance
Because aluminum is a relatively active metal, electroplating materials are more active than aluminum. Therefore, before electroplating, corresponding chemical transformations must be carried out, such as zinc dipping, zinc-iron alloy, zinc-nickel alloy, etc., so that zinc and zinc alloy have good bonding force between the bottom layer and the middle layer of cyanide copper plating. Due to the loose structure of die-casting aluminum, the surface part of die-casting aluminum can not be polished off, otherwise pinhole, acid spitting and peeling will occur.
III. The technological process of aluminum electroplating is as follows
Degreasing-> alkaline corrosion->; Activation-> zinc replacement->; Activation-> electroplating (such as nickel, zinc, copper, etc. )->; Chrome plating or passivation->; Drying.
1, common electroplating types of aluminum are
Nickel plating (pearl nickel, sand nickel and black nickel), silver plating (surface silver and thick silver), gold plating, zinc plating (colored zinc, black zinc and blue zinc), copper plating (blue drum copper, white tin copper, alkali copper, burnt copper and acid copper), chromium plating (white chromium, hard chromium and black chromium) and so on.
2. Use of common electroplating seeds
1) Black electroplating, such as black zinc and black nickel, is used for optical, electronic and medical devices.
2) Gold plating. Silver is the best conductor of electronic products, which can also improve the high decoration of products, but it is expensive. It is generally used for conducting electronic products, such as electroplating high-precision terminals.
3) Copper, nickel and chromium are the most popular mixed plating species in the field of modern science, and they are the most popular plating species in the world in terms of decoration and corrosion resistance. Low price, and can be used in sports equipment, lighting and most electronic industries.
4) Among the copper-based electroplating varieties, white tin copper was developed for environmental protection in 1970s and 1980s, and it is the first choice for jewelry industry because of its bright color. Bronze (lead, tin and copper can imitate gold, so it is a better decorative electroplating seed), but the anti-tarnishing performance of copper is relatively poor, so its development is relatively slow.
5) Zinc plating: The zinc coating is blue-white and easily soluble in acid and alkali. Because the standard potential of zinc is lower than that of iron, it can provide reliable electrochemical protection for steel. Zinc can be used as a protective layer for steel used in industrial atmosphere and marine atmosphere.
6) Hard chromium, the chromium coating deposited under certain conditions has high hardness and wear resistance, and the hardness reaches Hv900-1200 kg/mm. Chromium is the commonly used coating with the highest hardness, which can improve the wear resistance of parts and prolong the service life. Such as work, mold, quantity, fixture, etc. Therefore, this kind of electroplating is essential for the cylinder, oil pressure and transmission system.
3, common anomalies and improvement measures
1) peeling: the primary zinc replacement is not good, and the time is too long or too short. Take improvement measures to re-determine the operation parameters such as replacement time, bath temperature and bath concentration.
B, insufficient activation, improvement measures, change the activation mode.
C pretreatment is not thorough, and there is oil stain on the surface of the workpiece. Improve measures and strengthen pretreatment.
2) Rough surface: A. The dosage of brightener, softener and pinhole in electroplating solution is not appropriate, so the dosage of additives should be readjusted.
B the surface of the machine body itself is rough, so it should be polished again before electroplating.
3) The yellowing of the surface belongs to the trend of low potential, so the installation method is changed. Add an appropriate amount of oil displacement agent.
4) There are teeth on the surface: the electroplating solution is too dirty. Strengthen filtration and carry out proper bath treatment.
4. Quality requirements
1) The appearance is free of yellow, pinholes, burrs, blisters, bumps and scratches.
2) The film thickness is above 15um, the salt spray test lasts for 48 hours, the Delta military standard is above grade 9, and the potential difference is between 130- 150mv.
3) The binding force can pass the 60-degree bending test.
4) Products in special environment can be changed accordingly.
5, aluminum and aluminum alloy electroplating operation matters needing attention
1) aluminum alloy should be used as a hanger for electroplating aluminum parts;
2) Every working procedure of aluminum and aluminum alloy after etching must be carried out quickly, and the shorter the interval between working procedures of aluminum profiles in cabinets, the better, so as to avoid re-oxidation;
3) The second zinc dipping time should not be too long to avoid excessive corrosion;
4) Water washing must be clean;
5) Prevent power failure during electroplating.
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Section 4 aluminum painting.
Coating can be divided into dip coating, spray coating, flow coating, roll coating and brush coating, among which dip coating and spray coating are the main methods. Dip coating is electrophoretic coating, which uses electrochemical method to deposit colloidal particles of organic resin on the surface of workpiece to form transparent or organic coatings of various colors. Cathodic electrophoresis is a new technology developed in 1970s, and it is also the main technology in dip coating industry. Advantages: good corrosion resistance, strong anti-discoloration ability and good adhesion. Spraying can be divided into powder coating and liquid coating, among which electrostatic coating is a popular process in the industry at present.
First, the scope of the painting process
Because of its good corrosion resistance, low price and many colors (it can be made in any different colors), it is suitable for all aluminum parts, but the material structure is too loose, such as sand-turned products, which need scraping operation and the relative quality is poor.
1, the working principle of electrostatic spraying
Under the action of the pump, the paint enters the electric field and the paint particles are negatively charged. Under the action of atomizing air pressure, the coating becomes finer and more uniform, and then under the action of working air pressure, the coating is evenly sprayed on the surface of the workpiece under the action of rotating cup or nozzle. Because the distance between the spray gun and the workpiece is the same on the same vertical plane, the electric field intensity on the same interface is the same, and the positive and negative charges attract each other, the surface of the workpiece is coated with a uniform organic resin coating. Then, under the condition of high temperature baking, the resin reaches the state of leveling and curing. Firmly embedded in the surface of the workpiece to protect the workpiece.
2, aluminum plating process
Mechanical grinding-> degreasing-> deoxidation film->; Chromizing->; Powder spraying or liquid spraying->; Baking-> hanging-> full inspection-> packaging-> warehousing.
1) common anomalies in powder liquid operation and their treatment methods
Section 5, Electroless Plating of Aluminum Materials
First, the principle of electroless plating
Electroless plating is a plating method in which metal ions are reduced and deposited on the surface of parts in the same solution under the condition of no current (no external power supply) and through the redox effect of reducing agent. Therefore, electroless plating can be described as a controllable and autocatalytic chemical reduction process of deposited metal, and its general reaction formula is:
Second, the characteristics of electroless plating
With the development of industry, electroless plating has become a promising technology. Compared with other electroplating methods, electroless plating has the following characteristics:
1) can be plated on parts made of various materials such as metal, semiconductor and non-conductor.
2) No matter how complicated the geometry of the part is, a coating with uniform thickness can be obtained wherever the solution can touch.
3) For autocatalytic electroless plating, a thick coating can be obtained, and even electroforming can be carried out.
4) No current is needed.
5) The coating is compact and there are few pores.
6) Coatings usually have special chemical and mechanical properties.
Electroless plating has developed rapidly in industry and electronics industry because of its many advantages. Taking electroless nickel plating as an example, the introduction is as follows:
1) Electroless nickel plating Because sodium hypophosphite is used as reducing agent, the coating usually obtained is a nickel-phosphorus alloy. According to the different phosphorus content, it can be divided into low phosphorus (1%-4%), medium phosphorus (4%- 10%) and high phosphorus (10%- 12%). Plating solutions with different PH values can obtain coatings with different phosphorus content. When PH=4-5, medium phosphorus and high phosphorus alloys can be obtained. Low phosphorus and medium phosphorus alloys can be obtained in weak alkaline solution with PH=8- 10. Nickel-phosphorus alloy with phosphorus content above 8% is an amorphous coating, which has excellent corrosion resistance because it has no grain boundary. The hardness can reach HV= 1 150 when it becomes a mixture of amorphous and crystalline after heat treatment at 300-400 degrees. After heat treatment, the hardness of electroless plating is close to hard chromium, which is an ideal coating to replace hard chromium layer and a good plating seed for aluminum (it can be applied to all aluminum and aluminum alloy products, including forging, die casting, aluminum profiles and so on). Disadvantages: the electroplated seeds are brittle, but the plasticity of the products is greatly improved after heat treatment. (Generally, after heat treatment above 400℃ for four hours, its plasticity is greatly improved. )
2) Process flow of electroless nickel plating on aluminum:
Ultrasonic degreasing->; Oxide removal film->; The first zinc replacement is->; Harmony->; The second zinc replacement->; Electroless nickel plating->; Passivation->; Ultrasonic cleaning->; Baking-> Full Inspection-> Packaging
3) Rejection of unqualified coating:
Steel, aluminum, copper, plastics and other chemical nickel can be removed by concentrated nitric acid. However, the parts should be put into the tank after drying. If moisture is brought in, the base metal will be excessively corroded. The working temperature is below 35 degrees.
4) Quality requirements:
A. the film thickness is in the range of 5-30μ m.
B, salt spray test for more than 24 hours, reaching CNS standard level 9 or above.
C, through the 60-degree bending experiment, there is no peeling phenomenon.
D, appearance without bumps, scratches, water marks and other undesirable phenomena.
E, uniform film layer, no fog, white spots and exposed coating.
Section VI, Classification and Selection of Coating Conditions
From the perspective of anti-corrosion requirements, the design of surface treatment should be considered as follows:
1) precious metals (gold, platinum), stainless steel with chromium 18% or more, magnetic alloy materials, nickel-copper alloy, etc. , generally do not need to add protective layer.
2) Parts made of carbon steel, low alloy steel and cast iron are easy to corrode in the atmosphere and should be protected.
3) Parts made of copper and copper alloys shall be bright pickled, passivated, electroplated or painted for protection according to different service conditions. Precision parts made of phosphor bronze or beryllium bronze can be made without surface treatment.
4) Parts made of aluminum and aluminum alloy can be anodized and sealed. Small parts that are not suitable for anodic oxidation can be treated by chemical oxidation. Cast aluminum alloys can be protected by painting.
5) Parts made of zinc alloy can be protected by phosphating, passivation, electroplating or painting.
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Section 7. Plasma surface treatment
The metal-coated cardboard was modified by plasma surface processor to improve the surface adhesion and make it as easy as ordinary paper. Using conventional water-based cold glue can make coated or glazed cardboard reliably bonded on the box pasting machine, without local coating, local glazing, surface polishing and tangent, and without changing different special glue for different cardboard.
After plasma surface treatment, it can not only enhance the applicability of metal-coated cardboard to glue, but also achieve high-quality bonding without relying on special glue. But also improves the spreadability of the surface and prevents the generation of bubbles. The most important plasma surface treatment equipment of Shanghai Xuanyi Instrument Equipment Co., Ltd. is atmospheric plasma treatment, which can enable carton manufacturers to obtain high-grade products with better quality at lower cost and higher efficiency.
Characteristics of plasma cleaning machine, a plasma surface treatment equipment for metal coated paperboard products;
1, the film-coated folding carton is firmly bonded, and environmental-friendly water-based glue can be used to reduce the amount of glue and effectively reduce the production cost.
2. Under the normal process setting, no traces of treatment will be found on the surface. The plasma is close to normal temperature and will not produce any thermal effect on the surface.
3. When double-sided or multi-sided plastic boxes need to be treated, the system may be equipped with different numbers of spray guns to complete the pretreatment work.
4. The plasma itself is electrically neutral, and it will not burn the surface when treating the aluminized surface.
5. The product has the advantages of continuous operation, high efficiency, fast processing speed, reliable bonding and low cost.
6. The plasma power, treatment distance and cleaning speed can be adjusted for quality control.
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Section 8. Electrophoresis treatment of aluminum material
Color electrophoretic coating of aluminum is a new surface treatment process. It uses electrochemical method to deposit colloidal particles of organic resin on parts to form transparent or various colors of organic coatings. According to the different charging conditions of resin particles in electrophoretic paint after ionization, it can be divided into anode electrophoresis (resin particles become negative ions after ionization) and cathode electrophoresis (resin particles become positive ions after ionization).
Electrophoretic coating has excellent corrosion resistance (it can pass neutral salt spray test for more than 400 hours) and strong anti-discoloration ability; Good adhesion with the base material, and can be used for various mechanical processing; The coating is bright in color and can be made into various colors according to user's requirements, such as gold, brown, gun color, black and so on. Compared with paint, it has good construction performance and little pollution and harm to the environment. Therefore, it is used in automobile shells and various accessories, bicycle handlebars and accessories, various daily hardware accessories, furniture, handicrafts and so on. Because cathodic electrophoresis is advanced, we take cathodic electrophoresis as the main topic we will introduce below;
Cathodic electrophoretic coating is a complex electrochemical and colloidal chemical process. Electrophoretic paint itself is a multi-component system of colloid and suspension, which has two components: dispersed phase (resin, pigment particles) and continuous phase (water). Four processes of cathodic electrophoresis:
1, the positively charged water-soluble resin particles and their adsorbed pigments move to the cathode.
2. Electrodeposited positively charged resin particles reach the surface of the part (cathode), discharge to form water-insoluble deposits, and form a paint film after baking.
3. Electrodialysis water is dialyzed from sediment, and can be baked when the water content drops to 5%- 15%.
4. Electrolyzed water is electrolyzed by DC to release hydrogen and oxygen. Due to electrolysis, the permeability decreases, which affects the appearance of paint film, reduces the adhesion of paint film and increases power consumption. Therefore, the electrolysis of water should be weakened.
Electrophoresis process flow:
Degreasing-> descaling->; Chromizing->; Electrophoresis->; Drying-> packaging
Verb (abbreviation of verb) quality standard
1) The appearance is free of color difference, orange peel, pinholes, rainbows, bumps and scratches.
2) The film thickness is 40-60um, the salt spray test lasts for more than 400 hours, and the CNS standard is above Grade 9.
3) The film can pass the 60-degree bending test without peeling off.
4) Both the white dove test and the drop ball test can reach the national standard.