Aluminum alloy anodizing and surface treatment technology

Characteristics of Aluminum and Aluminum Alloys

1. Low density
Density of aluminum is about 2.7g/cm3, which is the second lightest metal in metal structure material only higher than magnesium, only 1/3 of iron or copper.
2. High plasticity
Aluminum and its alloys have good ductility, can be made into various shapes, plates, foils, tubes and wires by extrusion, rolling or drawing and other pressure processing methods.
3. Easy to strengthen
Strength of pure aluminum is not high, but it can be easily strengthened by alloying and heat treatment, high-strength aluminum alloy can be manufactured, and its strength can be comparable to that of alloy steel.
4. Good conductivity
Electrical and thermal conductivity of aluminum is second only to silver, gold, and copper. Assuming that relative conductivity of copper is 100, that of aluminum is 64, and that of iron is only 16. If calculated according to electrical conductivity of equal mass metals, aluminum is almost twice that of copper.
5. Corrosion resistance
Aluminum and oxygen have a very high affinity. Under natural conditions, protective oxides will be formed on the surface of aluminum, which has much better corrosion resistance than steel.
6. Easy to recycle
Melting temperature of aluminum is low, about 660℃, waste is easy to regenerate, recovery rate is extremely high, and energy consumption of recycling is only 3% of that of smelting.
7. Solderable
Aluminum alloy can be welded by inert gas protection method. After welding, mechanical properties are good, corrosion resistance is good, appearance is beautiful, and it meets requirements of structural materials.
8. Easy surface treatment
Aluminum can be treated by anodic oxidation coloring, which has high hardness, good wear resistance and corrosion resistance, good electrical insulation. Chemical pretreatment can also be carried out by electroplating, electrophoresis, spraying, etc. to further improve decorative and protective properties of aluminum.

Aluminum Surface Mechanical Pretreatment

1. Purpose of mechanical pretreatment
a. Provide good appearance conditions, improve quality of surface finishing; improve product grade; reduce influence of welding; produce decorative effects; obtain a clean surface.
2. Common methods of mechanical pretreatment
Commonly used mechanical pretreatment methods include polishing, sandblasting, brushing, and rolling. Which kind of pretreatment to use depends on the type of product, production method, initial state of surface and final finishing level.
3. Principle and function of mechanical polishing
Friction between high-speed rotating polishing wheel and workpiece generates high temperature, which causes deformation on metal surface, thereby smoothing convex and concave points on metal surface, and at the same time, extremely thin oxide film on metal surface that is instantly formed under oxidation of surrounding atmosphere is repeatedly ground down, so that it becomes brighter and brighter. Main function is to remove surface defects such as burrs, scratches, corrosion spots, blisters, and pores on the surface of workpiece. At the same time, fine unevenness on the surface of workpiece is further removed to make it have a higher gloss until mirror effect.
4. Principle and function of sandblasting
Use purified compressed air to spray dry sand or other abrasive grains on the surface of aluminum products to remove surface defects and present a uniform matte sand surface. Main functions: remove burrs, casting slag and other defects and dirt on the surface of workpiece; improve mechanical properties of alloy; obtain a uniform surface matting effect.
5. Principle and function of brushing
Brushing is to remove burrs, dirt, etc. on the surface of product by means of rotation of brushing wheel. For aluminum alloy drawing, it is to carry out wire drawing treatment on product, main purpose is to play a decorative role.
6. Principle and function of rolling light
Rolling is to put workpiece into a drum filled with abrasives and chemical solutions, use rotation of drum to rub workpiece and abrasive, workpiece and workpiece to achieve polishing effect.

Chemical Pretreatment of Aluminum

1. Definition and function of chemical pretreatment
Process of pre-treating aluminum surface with chemical solutions or solvents can effectively remove oil stains, pollutants and natural oxide films on original aluminum surface, so that aluminum can obtain a clean and evenly wet surface.
2. Common process flow of chemical pretreatment
Commonly used chemical pretreatment methods include degreasing, alkali washing, ash removal, fluoride sand surface treatment, water washing and other methods. According to use of aluminum to be treated and requirements for surface quality, different chemical pretreatment processes can be used.
3. Principle and function of degreasing
Oil will be hydrolyzed in acidic degreasing solution to generate glycerin and corresponding higher fatty acids. With assistance of a small amount of wetting agent and emulsifier, oil is more easily dissolved and degreasing effect is improved. After degreasing treatment, grease and dust on the aluminum surface can be removed, so that subsequent alkaline cleaning is relatively uniform.
4. Principle and function of alkali washing
Put aluminum material into a strong alkaline solution with sodium hydroxide as main component for etching reaction, further remove dirt on the surface, completely remove natural oxide film on aluminum surface, and reveal a pure metal matrix for subsequent anodes oxidation treatment.
5. Principle and function of ash removal
After alkali washing, surface of product often has a layer of metal compounds that are insoluble in alkali washing bath and its alkali washing products. They are a layer of taupe or gray black hanging ash. Purpose of ash removal is to remove this layer of hanging ash that is insoluble in lye, so as to prevent pollution of bath solution in subsequent anodic oxidation process.
6. Principle and function of fluoride sand surface treatment
Fluoride sand surface treatment is an acid etching process that uses fluoride ions to produce highly uniform and high-density pitting corrosion on the surface of aluminum materials. Purpose is to eliminate extrusion marks on the surface of product and generate a flat surface. However, due to serious environmental pollution problems in fluoride sand surface treatment process, it has not been promoted and used at present.

(Electro)chemical polishing and chemical conversion of aluminum

1. Role of chemical polishing or electrochemical polishing
Chemical polishing is an advanced finishing treatment method, which can remove slight mold marks and scratch lines on the surface of aluminum products, remove friction lines, thermal deformation layers, oxide films, etc. that may be formed during mechanical polishing, make rough surface smooth and obtain a mirror-like bright surface, improve decorative effect of aluminum products.
2. Principle of chemical throwing
Chemical polishing is to control selective dissolution of aluminum surface, so that microscopic protruding parts of aluminum surface are preferentially dissolved than concave parts, so as to achieve purpose of smooth and bright surface. Principle of electrochemical throwing is tip discharge, which is similar to other chemical throwing.
3. Role of chemical transformation
Chemical conversion is mainly used to protect aluminum and its alloys from corrosion. It can be used directly as a coating or as bottom layer of organic polymers, which not only solves adhesion between coating and aluminum, but also improves corrosion resistance of organic polymer coating.
4. Principle of chemical transformation
In chemical treatment solution, metal aluminum surface reacts with chemical oxidant in solution to form a chemical conversion film. Common chemical conversions are divided into chemical oxidation treatment, chromate treatment, phosphochromate treatment and chromium-free chemical conversion.
5. Introduction to Chemical Transformation
Aluminum can get a dense protective chemical oxide film in boiling water. This method is called chemical oxidation treatment, but due to film formation speed and performance, it is not mass-producible; chromium film formed by chromate treatment is aluminum chemical conversion film with the best corrosion resistance at present. It is not only commonly used as bottom layer of spraying, but also can be directly used as final coating of aluminum alloy, but its disadvantage is serious environmental pollution; phosphochromate treatment can satisfy bottom layer of spraying and trivalent chromium is non-toxic, which is currently used in 3C products; at present, industrial production mainly adopts chromium-free treatment of fluorine complexes containing titanium or (and) zirconium. Chromium-free treatment requires strict chemical pretreatment. At the same time, chromium-free film is colorless and transparent, and actual effect of chemical conversion cannot be judged by naked eye. Therefore, it is more dependent on reliable technology and strict control of manufacturing process. To sum up, chemical conversion most commonly used in 3C products is phosphochromate treatment.

Anodizing of aluminum alloy

1. Definition of anodizing
Anodizing is an electrolytic oxidation in which surface of an aluminum alloy is usually converted into an oxide film that has protective, decorative, and other functional properties.
2. Classification of anodized film
Oxide film is divided into two categories: barrier oxide film and porous oxide film. Barrier oxide film is a dense and non-porous thin oxide film close to metal surface. Thickness depends on applied voltage and generally does not exceed 0.1um. Porous oxide film is composed of a barrier layer and a porous layer. Thickness of barrier layer is related to applied voltage, and thickness of porous layer depends on electricity passing through. The most commonly used is porous oxide film.
3. Characteristics of anodized film
a. Structure of oxide film is a porous honeycomb structure. Porosity of film makes it have a good adsorption capacity. It can be used as bottom layer of coating and can also be dyed to improve decorative effect of metal.
b. Hardness of oxide film is high, hardness of anodic oxide film is very high, and its hardness is about 196-490HV, because high hardness determines wear resistance of oxide film is very good.
c. Corrosion resistance of oxide film. Aluminum oxide film is very stable in the air and soil, and has a strong binding force with substrate. Generally, it will be dyed and sealed or sprayed after oxidation to further enhance its corrosion resistance. .
d. Bonding force of oxide film, bonding force of oxide film to base metal is very strong, it is difficult to separate them by mechanical means, even if film layer is bent with metal, film layer still maintains a good bond with base metal, but plasticity of oxide film is small and brittleness is large. When film layer is subjected to a large impact load and bending deformation, cracks will occur, so this oxide film is not easy to use under mechanical action, and can be used as bottom layer of paint layer.
e. Insulation of oxide film, impedance of anodic oxide film of aluminum is high, thermal conductivity is also very low, thermal stability can be as high as 1500 degrees, and thermal conductivity is 0.419W/(m•K)—1.26W/(m• K). It can be used as dielectric layer of electrolytic capacitors or insulating layer of electrical products.

Aluminum oxide film formation process

1. The first stage of anodizing
In formation stage of non-porous layer, section ab, voltage increases sharply within period of power-on and off (several seconds to tens of seconds), reaching critical voltage (maximum voltage), indicating that a continuous, non-porous film layer is formed on the surface of anode at this time. Resistance of non-porous layer is large, which hinders continuous thickening of film. Thickness of non-porous layer is proportional to formation voltage, and dissolution rate of oxide film in electrolyte is inversely proportional. Thickness is about 0.01 to 0.1 microns.
2. Second stage of anodizing
During formation of porous layer, bc section will be the first to dissolve holes in the thinnest part of film, electrolyte can reach fresh surface of aluminum through these holes, electrochemical reaction can continue, resistance resistance will decrease, voltage will drop( (decrease range is 10-15% of the highest value), and a porous layer will appear on the film.
3. Third stage of anodizing
Porous layer thickens, cd section, at this time voltage rises steadily and slowly, non-porous layer is continuously dissolved into a porous layer, and a new non-porous layer is growing, so porous layer is constantly thickening. When formation rate and dissolution rate reach a dynamic balance, thickness of film will no longer increase, and reaction should stop at this time.

Aluminum alloy anodizing process

1. Common process of anodizing
Commonly used processes for anodizing aluminum alloys are: sulfuric acid anodizing process, chromic acid anodizing process, oxalic acid anodizing process and phosphoric acid anodizing process. The most commonly used is sulfuric acid anodizing.
2. Sulfuric acid anodizing
At present, anodic oxidation process widely used at home and abroad is sulfuric acid anodic oxidation. Compared with other methods, it has great advantages in production cost, oxide film characteristics and performance. It has advantages of low cost, good film transparency, good corrosion resistance and friction resistance, and easy coloring. It uses dilute sulfuric acid as electrolyte to anodize product. Thickness of film can reach 5um-20um. Film has good adsorption, colorless and transparent, simple process and convenient operation.
3. Chromium anodizing
Film obtained by chromic acid anodization is thinner, only 2-5um, which can maintain original precision and surface roughness of workpiece; porosity is low, it is difficult to dye, and it can be used without sealing holes; soft film, poor wear resistance but good elasticity; corrosion resistance is strong, and solubility of chromium to aluminum is small, so that residual liquid in pinholes and crevices has less corrosion on the parts. It is suitable for structural parts such as castings. This process is widely used in military. At the same time, quality of parts can be inspected, and brown electrolyte will flow out at crack, which is obvious.
4. Oxalic acid anodizing
Solubility of oxalic acid to oxide film of aluminum is small, so porosity of oxide film is low, wear resistance and electrical insulation of film layer are better than that of sulfuric acid film; but cost of oxalic acid oxidation is 3 to 5 times that of sulfuric acid; at the same time, oxalic acid will be reacted at cathode and anode, resulting in poor stability of electrolyte; color of oxalic acid oxide film is easy to change with process conditions, resulting in color difference in product, so application of this process is limited. However, oxalic acid is more commonly used as a sulfuric acid oxidation additive.
5. Phosphoric acid anodizing
Oxide film dissolves more in phosphoric acid electrolyte than sulfuric acid, so oxide film is thin (only 3um) and pore size is large. Because phosphoric acid film has strong water resistance, it can prevent adhesive from aging due to hydration and make bonding force of adhesive better, so it is mainly used for surface treatment of printed metal plates and pretreatment of aluminum workpieces.

Aluminum alloy hard anodizing

1. Characteristics of hard oxide film
Compared with ordinary oxide film, hard anodic oxidation of aluminum alloy has following characteristics: thicker oxide film (generally not less than 25um), high hardness (greater than 350HV), better wear resistance, lower porosity, higher breakdown voltage, and surface smoothness may appear a little worse.
2. Process characteristics of hard anodizing
There is no essential difference between hard anodic oxidation and ordinary oxidation in terms of principle, equipment, process and detection. Hard oxidation seeks to reduce solubility of oxide film, main features are:
a. Temperature of bath solution is low (generally about 20 degrees, and hardness is below 5 degrees). Generally, hardness of oxide film formed by low temperature is high
b. Concentration of bath solution is low (concentration of ordinary sulfuric acid is 20%, concentration of hard acid is less than 15%), and solubility of membrane is small when concentration is low.
c. Organic acid is added to bath, oxalic acid or tartaric acid is added to sulfuric acid, etc.
d. Applied voltage and current are high (ordinary current 1.5A/dm2, voltage below 18V, hard current 2~5A/dm2, voltage above 25V. Up to 100V)
e. Applied voltage should adopt method of gradually increasing voltage. Because of its high voltage, high current and long processing time, it consumes a lot of energy. At the same time, hard oxidation often uses pulse power supply or special waveform power supply
3. Hard anodizing of cast aluminum alloy
Casting aluminum alloys usually require hard anodizing to improve their performance. Aluminum/silicon alloys and aluminum/copper alloys are commonly used in casting aluminum alloys. Aluminum silicon alloys have good casting performance and wear resistance, are used in the largest amount. It is widely used in structural parts. Sometimes copper and magnesium are added to improve mechanical properties and heat resistance. Aluminum-copper series is also a commonly used casting alloy, which is mainly used for sand castings with large dynamic and static loads and uncomplicated shapes. Casting aluminum alloys need to improve electrolyte and power waveform due to non-metallic elements. Electrolyte can generally add some metal salts or organic acids to sulfuric acid, sulfuric acid-oxalic acid-tartaric acid solution, sulfuric acid-dry oil solution; power supply form is generally changed to AC and DC superposition, asymmetric current, pulse current, etc., and pulse effect is better. Before oxidation of electroformed parts, water chestnut should be guided and deburred to prevent current concentration.

Aluminum Alloy Micro-arc Oxidation (MAO)

1. Principle of micro-arc oxidation technology:
Micro-arc oxidation, also known as micro-plasma surface ceramicization technology, refers to use of arc discharge to enhance and activate reaction on anode on the basis of ordinary anodic oxidation, so as to form a high-quality reinforced ceramic film on the surface of workpiece made of aluminum, titanium, magnesium metal and its alloys by using arc discharge. By applying a voltage on the workpiece with a special micro-arc oxidation power supply, metal on the surface of workpiece interacts with electrolyte solution to form a micro-arc discharge on the surface of workpiece. Under action of high temperature, electric field and other factors, a ceramic film is formed on metal surface to reach the workpiece. Under aaction of high temperature, electric field and other factors, a ceramic film is formed on metal surface to achieve purpose of strengthening surface of workpiece
2. Characteristics of Micro-arc Oxidation
a. Surface hardness of material is greatly improved (HV>1200), exceeding hardness of high-carbon steel, high-alloy steel and high-speed tool steel after heat treatment;
b. Good wear resistance;
c. Good heat resistance and corrosion resistance (CASS salt spray test > 480h), which fundamentally overcomes shortcomings of aluminum, magnesium and titanium alloy materials in application, so this technology has broad application prospects;
d. It has good insulation performance, and insulation resistance can reach 100MΩ.
e. Process is stable and reliable, and equipment is simple. Reaction is carried out at room temperature, operation is convenient and easy to master.
f. Ceramic film is grown in situ on substrate, combination is firm, and ceramic film is dense and uniform.
3. Application of Micro-arc Oxidation
Micro-arc oxidation is a new aluminum alloy surface treatment technology. It combines ceramic properties of aluminum oxide and metallic properties of aluminum alloy to make surface of aluminum alloy have better physical and chemical properties. However, due to technical and economic reasons, it is not widely used in our country at present. However, due to special properties of oxide film, it can be used in many fields, including aviation and automobile engines, petrochemical industry, textile industry and electronics industry.
Insufficiency of micro-arc oxidation: micro-arc oxidation will cause spark discharge and spark corrosion, making surface of product rough, and rough layer must be worn off during use, resulting in waste. Energy consumption is relatively high, which is five times that of ordinary oxidation.

Electrolytic Coloring of Aluminum Alloy Oxide Film

1. Common coloring process of aluminum alloy oxide film:
Commonly used coloring processes for aluminum alloys can be roughly divided into three categories:
a. Overall coloring method: including natural coloring and electrolytic coloring. Natural coloring refers to oxidation of added components (Si, Fe, Mn, etc.) in aluminum alloy during anodic oxidation process, resulting in coloring of oxide film. Electrolytic color development refers to coloring of oxide film caused by changes in composition of electrolyte and electrolytic conditions.
b. Dyeing method: based on primary oxide film, oxide film is dyed with inorganic pigments or organic dyes.
c. Electrolytic coloring method: based on primary oxide film, electrolytic coloring is carried out with direct current or alternating current in a solution containing metal salts. Weather resistance, light resistance and service life of electrolytic coloring are better than dyeing method, and its cost is much lower. For the overall coloring method, it is widely used in coloring of architectural aluminum profiles. Industrialized electrolytic coloring bath solutions at home and abroad are basically two types of nickel salt and tin salt (including tin-nickel mixed salt) solutions, and colors are generally from light to dark bronze.
2. Principle of electrolytic coloring
Regular and controllable micropores of porous anodized film deposit very fine metal and (or) oxide particles at the bottom of pores by electrolytic coloring, and different colors can be obtained due to scattering effect of light. Depth of color is related to number of deposited particles, that is, to coloring time and applied voltage. Generally speaking, colors of electrolytic coloring are similar from champagne, light to dark bronze to black, and hues are not exactly same, which is related to size distribution of precipitated particles. At present, electrolytic coloring is only available in bronze, black, golden yellow, and maroon.
3. Application of electrolytic coloring
Sn salt and Sn-Ni mixed salt are main coloring methods in my country and Europe and United States. Salt is SnSO4, which is colored by precipitation of Sn2+ electrolytic reduction in micropores of anodic oxidation; but Sn2+ has poor stability and is easily oxidized into Sn4+ without coloring ability. Therefore, the key to tin salt coloring is composition of bath solution and stability of tin salt, which is the key to this process. Tin salt is not sensitive to impurities, has better coloring uniformity, and has little water pollution. Ni salt electrolytic coloring is relatively common in Japan. It is often used in light colors (imitation stainless steel color, light champagne color). It has fast coloring speed and good bath stability, but it is sensitive to impurities. At present, equipment for removing impurities is mature, but it requires a large one-time investment.

Dyeing of Aluminum Alloy Oxide Film

1. Definition of aluminum alloy oxide film dyeing
Dyeing method is to immerse freshly oxidized aluminum alloy in a solution containing dyes immediately after cleaning, and pores of oxide film are dyed with various colors due to adsorption of dyes. This process is fast in coloring, bright in color, and easy to operate, but it needs to be sealed after dyeing.
2. Dyeing requirements for oxide film
a. Oxide film obtained by aluminum in sulfuric acid solution is colorless and porous, and is most suitable for dyeing. Oxalic acid oxide film itself is yellow and can only be dyed in dark colors. Chromic acid film has low porosity and film itself is gray and can only be dyed in dark colors.
b. Oxide film must have a certain thickness, minimum requirement is greater than 7um, and thinner oxide film can only be dyed with a very light color.
c. Oxide film should have a certain degree of porosity and adsorption, so hard oxide film and chromic acid conventional oxide film are not suitable for dyeing.
d. Oxide film should be complete and uniform, and there should be no defects such as scratches, trachoma, and pitting corrosion.
e. Film layer itself has a suitable color, and there is no difference in metallographic structure, such as different grain sizes or severe segregation, etc.
3. Staining mechanism of oxide film
a. Dyeing mechanism of organic dyes: based on adsorption theory of substances, it is divided into physical adsorption and chemical adsorption; Physical adsorption refers to adsorption of molecules or ions by electrostatic force; adsorption by chemical force (covalent bond, hydrogen bond, chelate bond, etc. generated by reaction) is called chemical adsorption. Physical adsorption requires low temperature, and high temperature is easy to desorb; chemical adsorption is carried out at a certain temperature.
b. Dyeing mechanism of inorganic dyes: usually carried out at room temperature, workpiece is first immersed in one inorganic salt solution in a certain order, then immersed in another inorganic salt solution, so that these inorganic substances undergo chemical reactions in membrane pores to form water-insoluble colored compounds, fill pores of oxide film and seal membrane pores (in some cases, sealing process can be omitted ). Color range of inorganic dyes is limited, and color is not bright enough, but temperature resistance and light resistance are very good.
4. Fading of unqualified dyed film
After dyeing and before sealing, defects can be removed by nitric acid 27% (mass fraction) or 5ml/l sulfuric acid at 25 degrees.

Hole Sealing of Aluminum Alloy Oxide Film

1. Definition of aluminum alloy oxide film sealing
Physical or chemical treatment process of oxide film after aluminum anodic oxidation to reduce porosity and adsorption capacity of oxide film, so as to seal dye in micropores, at the same time improve corrosion resistance and wear resistance of film. In construction industry, countries around the world basically use three processes for sealing oxide films: high-temperature steam, cold sealing, and electrophoretic coating. According to sealing principle, there are three main categories: hydration reaction, inorganic filling or organic filling.
2. Heat sealing process
a. Boiling water sealing: In pure water close to boiling point (temperature above 95 degrees, deionized water), amorphous alumina is converted into hydrated alumina through hydration reaction of alumina. Since hydrated alumina is 30% larger than original volume, volume expansion makes micropores of oxide film filled and closed.
b. High-temperature steam sealing: principle is same as boiling water sealing, advantages: fast speed, less dependence on water quality, less white ash, less risk of fading. Equipment needs to be airtight to ensure temperature and humidity. Generally, temperature is 115~120 degrees, and pressure is 0.7~1atm. Cost is high!
3. Cold sealing process
Cold sealing is the most commonly used and most basic hole sealing technology in my country. Operating temperature is 20~25 at room temperature, time and heat sealing ratio are shortened by half. It relies on deposited filler in micropores to seal holes. The most mature process is cold sealing process with nickel fluoride as main component. After cold sealing is completed, hot water aging (60-80 degrees deionized hot water, 10-15 minutes) treatment is required to modify product to avoid high-temperature microcracking of product.
4 medium temperature hole sealing process
Aiming at defects of heat sealing and cold sealing process, we developed medium-temperature inorganic salt sealing technology, mainly including chromate sealing, silicate sealing and acetate sealing.
a. Aluminate sealing: can provide good anti-corrosion effect, especially for die-casting aluminum alloy and high copper aluminum alloy (PH6.32~6.64. about 10min)
b. Silicate sealing: Since white ash or discoloration often occurs after silicate sealing, this process is not currently used unless there are special needs
c. Nickel acetate sealing: Quality of sealing is relatively good, and it is widely used in North America. Except for small parts with organic dyeing, it is basically not used in my country.

Electrophoretic coating of aluminum alloy oxide film

1. Definition of electrophoretic coating
Charged paint particles in solution form a coating by electrophoresis under action of direct current. Electrophoretic coating of aluminum generally adopts anodic electrophoresis. Electrophoresis is a process with low pollution and low energy consumption. It has characteristics of smooth coating film, good water resistance and chemical resistance, and is easy to realize automation. It is suitable for coating workpieces with complex shapes, edges, corners or holes.
2 Electrophoretic coating process principle
Electrophoretic coating is divided into anodic electrophoresis and cathodic electrophoresis. Water-soluble resin of anodic electrophoretic coating is a carboxylate of high-valent acid, usually ammonium carboxylate. Electrophoretic coatings can be ionized into charged particles in acid or alkaline solution and dispersed in water. Under action of direct current, charged resin particles will adhere to a layer of resin film on metal surface. Main component of electrophoretic coating of aluminum alloy oxide film is a water-soluble acrylic polymer compound, which is a translucent emulsion. Electrophoretic coating process is an electrochemical process, which mainly includes four processes: electrophoresis, electrodeposition, electroosmosis and electrolysis.
3. Aluminum alloy electrophoresis process
Feeding-greasing-water washing-alkali etching----water washing (2 times)---ash removal------- water washing---anodic oxidation----water washing (2 times)-electrolytic coloring--water washing—hot pure water washing—high purity water washing—draining—electrophoretic coating—R01 cycle washing—R02 cycle washing—draining, baking, curing, and cooling
4. Characteristics of electrophoretic coating
Advantages: high degree of automation of coating process, high paint recovery rate, high coating efficiency, uniform film thickness, which can reduce unnecessary waste and bath solution is easy to coat. Conditions are easy to control and manage. Film thickness is uniform, film thickness is high, inner plate is well protected against rust, there will be no bad phenomena such as missing coating and flow marks.
Disadvantages: One-time investment in equipment is large, object to be coated must be conductive to replace coating, and it is difficult to change color.

Gud Mould Industry Co., Ltd