1. Localized dark spots or streaks, as well as anomalies or cavitations. After the anodizing treatment of the aluminum alloy products, localized non-oxidized films occur, showing black spots or streaks that are visible to the naked eye, and the oxide film has bulging or cavities. Although such failures are rare, they also occur. The reason for this is usually related to the composition, structure and phase homogeneity of aluminum and aluminum alloys, or to the dissolution of certain metal ions or suspended impurities in the oxidizing solution. The chemical composition, microstructure, and metal phase uniformity of aluminum and aluminum alloys can affect the oxide film formation and performance. The oxide film of pure aluminum or aluminum-magnesium alloy easily produces a high-quality film. The aluminum-silicon alloy or copper-containing high-strength aluminum alloy produces a dark, grayish oxide film with poor gloss. If the surface phase structure is not uniform, tissue segregation, impurity segregation or uneven heat treatment caused by improper organization, etc., it is easy to produce selective oxidation or selective dissolution, resulting in poor quality oxide film. For example, if the local silicon content in the aluminum alloy material is segregated, local oxidation-free films or black spot streaks or local selective dissolution of holes are often caused. In addition, if there are suspended impurities in the electrolyte, dust particles or copper, iron and other metal impurities, ion content is too high, the oxide film will often appear black spots or black streaks, affecting the anodized film corrosion protection.
2. Oxide film is incomplete, local no film or burned anodized parts treated with the same groove, some parts without oxide film or film thin or incomplete, but in the fixture and the parts where there is a burning loss erosion phenomenon.
Such failures often occur in sulfuric acid anodizing process practice, which seriously affects the anodizing quality of aluminum alloy parts. Caused by this failure are: 1 inappropriately clamped position. Due to the improper positioning of the clamps, oxygen does not escape from the localized surface when anodized, resulting in stifling gas without oxide film. When mounting, care should be taken to select an appropriate position so that the concave portion of the part is tilted upward or upward so that no oxide film failure can be avoided. 2 There are attachments on the surface of the parts. If the surface of the component before the anodization is covered with a transparent viscous material such as adhesive tape, it will not come off during the anodization, but will fall off when the film is closed. As a result, there will be no oxide film on the adsorbent, and the operator will perform the pretreatment process. Care should be taken to remove such substances. 3 Oxidation solution components are too thin. The oxidizing solution composition is too dilute, resulting in no oxide film formation at the local current of the oxidized part being too small, and the high sulfuric acid concentration can be analyzed and depleted to eliminate this failure.
Due to the better insulation of the aluminum oxide film, the aluminum alloy parts must be ran and mounted on universal or special fixtures before anodizing to ensure good electrical conductivity. Conductive rods should use copper or copper alloy materials and must ensure sufficient contact area. At the contact between the fixture and the part, it is necessary to ensure the free passage of current, and to minimize the contact marks between the fixture and the part. If the contact area is too small and the current density is too high, overheated parts and jigs may burn.
3. Oxidation film loose powder aluminum alloy sulfate after anodizing, the oxide film was loose powder and even touched on the hand, especially after the filling of the house is closed, the surface of the parts appear severe powder layer, poor corrosion resistance.
In the process of anodic oxidation of aluminum alloy, the formation and dissolution of the oxide film are performed at the same time. The chemical dissolution of the oxide film will cause loosening of the oxide film, and even produce a loose powdery oxide film. The rate of dissolution of the oxide film has a significant influence on the temperature of the oxidizing solution and accelerates as the temperature of the solution increases. Therefore, this type of failure occurs mostly in the summer, and in particular, sulfate anodizing tanks that do not have a cooling device are often treated with 1-slot to 2-slot components. Loose pulverization occurs and significantly affects the quality of the oxide film. Due to the large resistance of the aluminum alloy anodic oxidation film, a large amount of Joule heat is generated during the anodic oxidation process. The higher the cell voltage, the greater the heat generation, and the resulting rise in the electrolyte temperature. Therefore, in the anodizing process, stirring or cooling devices must be used to keep the electrolyte temperature within a certain range. Under normal circumstances, the temperature should be controlled at 13 °C ~ 26 °C, the quality of the oxide film is better. If the electrolyte temperature exceeds 30°C, the oxide film will be loosely powdered and the film quality will be poor, and the phenomenon of "burning" will occur when the temperature is too high. In addition, when the electrolyte temperature is constant, the anode current density must also be limited, because the anode current density is too high, the temperature rises sharply, the oxide film is also easy to loose in the form of powder or sand, the quality of the oxide film is very unfavorable.
In addition, the long anodizing time and the strong concentration of the solution also produce a loose anodic oxide film. When the current density is too high or the voltage is too high, the Joule heat generated will cause the aluminum alloy parts to heat, causing the temperature of the solution around the parts to rise, thereby speeding up the chemical dissolution of the oxide film, causing the oxide film to loosen or generate a powdery oxide film. Therefore, strict control of the process specification is an important factor in preventing the anodic oxide film from becoming loose.
Aluminum anodic oxidation processes such as washing may bring chloride ions to the oxidizing solution, and sulfuric acid may also contain chloride ions, which may lead to increased chloride ion content in the oxidizing solution, resulting in loose oxide film.
When adding sulfuric acid to the oxidation tank, uneven stirring of the solution can also cause the anodized parts in the same tank. Some oxide films are too thin, and some oxide films are loose and have powdery ash.
The measures to eliminate the above faults are: Strict process specification operation, electrolyte temperature is too high should try to reduce the temperature, stirring or start cooling equipment, and control the temperature difference within (20 ± 2) °C. If the oxidation treatment time is too long, the anodizing time should be shortened; if the current density is too high, the current density should be reduced. After adding sulfuric acid in the solution should be fully compressed into the compressed air and power treatment; when the solution. If the content of chloride ion is too high, you can troubleshoot by diluting the solution or partially replacing the solution.
4. The oxide film is dull. The spot corrosion of the aluminum alloy sulfate anodic oxide film is dull, sometimes with pitting corrosion and severe black spot corrosion.
Such failures are often accidental and have special causes. In the process of anodizing of aluminum alloy, power is cut off in the middle and power is recharged. A double oxide film is often formed to make the oxide film dark and dull; while parts that are half-way powered off stay in the cleaning tank for too long, the acidity of the cleaning water tank is too high, and the water quality is not net. , With a lot of suspended solids, aluminum alloy parts often cause spot corrosion, dark spots and other failures. The increase in the amount of aluminum ions dissolved in the sulfuric acid solution also leads to the deterioration of the transparency of the oxide film. Usually, the amount of aluminum contained in the sulfuric acid solution is approximately l09/L. Mixing excessive Cl ions in the aluminum oxidation solution may also cause anodic oxidation of the aluminum alloy parts to cause spot corrosion and other failures.
5. Anodic oxide film is thin or red ash is hanging, and the corrosion resistance of the film layer is poor. The reasons for this failure are many, including the following aspects.
(1) Sulfuric acid content and operating conditions do not comply with the process specification. If the anodizing current density is low, the voltage is low, and the oxidation time is short, the oxide film formed on the surface of the aluminum alloy is relatively thin. If the concentration of the solution is low, the ions in the solution are small and the conductivity of the solution is small. To achieve the same current density, the solution of the low concentration solution has a higher cell voltage than the high concentration cell voltage, and the anodizing of the sulfuric acid is generally controlled by the voltage. Therefore, when the concentration of the solution is low, the current density is small at the specified voltage, and the resulting oxide film is also thin. When the temperature of the solution is low, the viscosity of the solution is large, the ion movement is slow, and the conductivity of the solution is small. Under the specified voltage, the current density is small, and the resulting oxide film is, of course, thin. On the contrary, the oxide film is thick, but the dissolution of the oxide film is also accelerated, and a loose powdery oxide film is formed.
(2) The parts are too loose, and the jig and the conductive rod are in poor contact. Checking the mounting condition of the aluminum alloy parts will reveal that the parts are too loosely clamped and the electrical conductivity is poor, which also causes the anodized film layer to become thin. In addition, the old oxide film on the jig is not removed, and the parts are clamped on the jig with a thin oxide film, which also causes poor conductivity. The oxide film formation rate becomes slow and the oxide film becomes thin.
(3) Anodizing solution contains too much copper and iron ions. Because the anodization process includes aluminum alloy surface dissolution and oxide film formation, such as some high-strength aluminum alloy materials, copper, manganese, iron, silicon and other elements, in the anodization process, copper and iron ions dissolved into the solution is possible With the increase of the use time of the anodizing solution, the content of copper ions in the solution will increase, which will affect the thickness of the oxide film or surface ash.
The measures to eliminate such failures are: strict control of the oxidation process specification; pay attention to the removal of the residual oxide film on the surface of the rack and ensure contact between the rack and the part. The problem of excessively high contents of copper and iron ions in the plating solution can be solved by increasing the area of ​​the cathode and applying a small current electrolytic treatment or renewing the oxidation solution.
6. Parts and fixtures in contact with the burn, parts of the local place there are electric shock burns This failure is caused by the aluminum alloy parts and the cathode contact short circuit, parts of the short-circuit caused by contact with each other. Therefore, it is necessary to strengthen the contact inspection between the anodized parts and the fixture. Before the fixture is used, it must be cleaned. It must be clamped with the parts to ensure that the parts conduct well. When placing parts in the oxidation tank, pay attention to the distance from the cathode to avoid contact. In addition, it is necessary to prevent parts from coming into contact with each other to cause a short circuit and increase the distance between parts.
7. There are black spots (black streaks) or reticulate foam patterns on the oxide film. The main causes of this failure are: After the parts are chemically deoiled, the light leakage process is oxidized and the water glass left on the parts forms silicic acid. As a result, the chemical degreasing fluid is not clean during heat treatment; there are oil stains or other contaminants on the surface of the parts; suspended impurities are contained in the oxidizing solution; plugging is performed after the oxidized parts are not washed; the surface of the solution has suspended impurities, copper and Too much iron impurities.
Excluding such failures requires thorough pretreatment; to strengthen the cleaning of oxidized parts, and to clean them immediately after oxidation, to avoid the treatment liquid or impurities remaining on the surface of the oxide film; to remove or renew the partial oxidation solution to reduce impurities in the solution.
8. Oxidized parts are easily filled with watermarks and watermarks after filling with hot water. The reasons for this breakdown of the oxide film after filling with potassium dichromate are as follows: the temperature of the filling and sealing solution is too low and the filling time is short; the pH value of the solution is not appropriate Blocking solution too much aluminum hydroxide, SO42- content is too high; anodizing temperature is too high to cause the oxide film is too thin, the film hole was open and so on.
Excluding such failures is mainly aimed at adjusting the pH value of the closed filling solution, strictly controlling the composition and process conditions of the solution, checking and correcting the contents of SO42- and aluminum hydroxide in the sealing solution, controlling the anodizing process conditions, and increasing the oxidation time.
9. After the anodic oxidation, the film will appear red or blue after dyeing. The main reasons for the red or blue dyeing of the film after oxidation are:
(1) The oxide film has poor adsorption performance. When the black oxide film was dyed with the acid black ATT dye, a reddish blue defect occurred. Acidic black ATT dyes are composed of 70% of acidic blue black lOB and 30% of acidic orange II molecular structure, so when the anodized film has small pores and poor absorption performance, the small molecule of acidic orange II is easily absorbed by the oxide film. The acid orange II in the film exceeds the dye ratio, so the color becomes red.
(2) The effect of the surface state of the sheet and extruded parts. Before the anodic oxidation, the parts should be alkali-etched to remove the surface crust to obtain a uniform black color. Otherwise, red or black flowers will also be obtained. For aluminum alloy parts with high silicon content, it can be immersed for about 20s in 40mL/L ~ 50mL/L nitric acid and about 10mL/L of hydrofluoric acid solution to dissolve impurities, leaving a thin layer of purer aluminum. In order to improve the performance of the anodized film, it has a good adsorption performance, and a uniform black color is obtained.
(3) Improper pH of the dyeing solution. The pH value of the dyeing solution has a great influence on the dyeing of the oxide film, because the absorption properties of the various dyes have their own different pH values. If the pH value is close to 7, the acid blue-black lOB has good adsorption performance, while the acidic orange II has poor adsorption performance, so the color is bluish. When the pH is about 4.5, the acid blue-black lOB has poor adsorption capacity and acidity. Orange II has a strong adsorption capacity, so the color is reddish.
The methods to eliminate this kind of failure include: strengthening the treatment before oxidation; appropriately prolonging the anodizing time, increasing the pores of the oxide film so that the large acid blue black 10B can be absorbed by the oxide film; controlling the pH of the dyeing solution, avoiding To open the value of 7 or 4.5, it is generally better to control about 3.6 or 5-6.
2. Oxide film is incomplete, local no film or burned anodized parts treated with the same groove, some parts without oxide film or film thin or incomplete, but in the fixture and the parts where there is a burning loss erosion phenomenon.
Such failures often occur in sulfuric acid anodizing process practice, which seriously affects the anodizing quality of aluminum alloy parts. Caused by this failure are: 1 inappropriately clamped position. Due to the improper positioning of the clamps, oxygen does not escape from the localized surface when anodized, resulting in stifling gas without oxide film. When mounting, care should be taken to select an appropriate position so that the concave portion of the part is tilted upward or upward so that no oxide film failure can be avoided. 2 There are attachments on the surface of the parts. If the surface of the component before the anodization is covered with a transparent viscous material such as adhesive tape, it will not come off during the anodization, but will fall off when the film is closed. As a result, there will be no oxide film on the adsorbent, and the operator will perform the pretreatment process. Care should be taken to remove such substances. 3 Oxidation solution components are too thin. The oxidizing solution composition is too dilute, resulting in no oxide film formation at the local current of the oxidized part being too small, and the high sulfuric acid concentration can be analyzed and depleted to eliminate this failure.
Due to the better insulation of the aluminum oxide film, the aluminum alloy parts must be ran and mounted on universal or special fixtures before anodizing to ensure good electrical conductivity. Conductive rods should use copper or copper alloy materials and must ensure sufficient contact area. At the contact between the fixture and the part, it is necessary to ensure the free passage of current, and to minimize the contact marks between the fixture and the part. If the contact area is too small and the current density is too high, overheated parts and jigs may burn.
3. Oxidation film loose powder aluminum alloy sulfate after anodizing, the oxide film was loose powder and even touched on the hand, especially after the filling of the house is closed, the surface of the parts appear severe powder layer, poor corrosion resistance.
In the process of anodic oxidation of aluminum alloy, the formation and dissolution of the oxide film are performed at the same time. The chemical dissolution of the oxide film will cause loosening of the oxide film, and even produce a loose powdery oxide film. The rate of dissolution of the oxide film has a significant influence on the temperature of the oxidizing solution and accelerates as the temperature of the solution increases. Therefore, this type of failure occurs mostly in the summer, and in particular, sulfate anodizing tanks that do not have a cooling device are often treated with 1-slot to 2-slot components. Loose pulverization occurs and significantly affects the quality of the oxide film. Due to the large resistance of the aluminum alloy anodic oxidation film, a large amount of Joule heat is generated during the anodic oxidation process. The higher the cell voltage, the greater the heat generation, and the resulting rise in the electrolyte temperature. Therefore, in the anodizing process, stirring or cooling devices must be used to keep the electrolyte temperature within a certain range. Under normal circumstances, the temperature should be controlled at 13 °C ~ 26 °C, the quality of the oxide film is better. If the electrolyte temperature exceeds 30°C, the oxide film will be loosely powdered and the film quality will be poor, and the phenomenon of "burning" will occur when the temperature is too high. In addition, when the electrolyte temperature is constant, the anode current density must also be limited, because the anode current density is too high, the temperature rises sharply, the oxide film is also easy to loose in the form of powder or sand, the quality of the oxide film is very unfavorable.
In addition, the long anodizing time and the strong concentration of the solution also produce a loose anodic oxide film. When the current density is too high or the voltage is too high, the Joule heat generated will cause the aluminum alloy parts to heat, causing the temperature of the solution around the parts to rise, thereby speeding up the chemical dissolution of the oxide film, causing the oxide film to loosen or generate a powdery oxide film. Therefore, strict control of the process specification is an important factor in preventing the anodic oxide film from becoming loose.
Aluminum anodic oxidation processes such as washing may bring chloride ions to the oxidizing solution, and sulfuric acid may also contain chloride ions, which may lead to increased chloride ion content in the oxidizing solution, resulting in loose oxide film.
When adding sulfuric acid to the oxidation tank, uneven stirring of the solution can also cause the anodized parts in the same tank. Some oxide films are too thin, and some oxide films are loose and have powdery ash.
The measures to eliminate the above faults are: Strict process specification operation, electrolyte temperature is too high should try to reduce the temperature, stirring or start cooling equipment, and control the temperature difference within (20 ± 2) °C. If the oxidation treatment time is too long, the anodizing time should be shortened; if the current density is too high, the current density should be reduced. After adding sulfuric acid in the solution should be fully compressed into the compressed air and power treatment; when the solution. If the content of chloride ion is too high, you can troubleshoot by diluting the solution or partially replacing the solution.
4. The oxide film is dull. The spot corrosion of the aluminum alloy sulfate anodic oxide film is dull, sometimes with pitting corrosion and severe black spot corrosion.
Such failures are often accidental and have special causes. In the process of anodizing of aluminum alloy, power is cut off in the middle and power is recharged. A double oxide film is often formed to make the oxide film dark and dull; while parts that are half-way powered off stay in the cleaning tank for too long, the acidity of the cleaning water tank is too high, and the water quality is not net. , With a lot of suspended solids, aluminum alloy parts often cause spot corrosion, dark spots and other failures. The increase in the amount of aluminum ions dissolved in the sulfuric acid solution also leads to the deterioration of the transparency of the oxide film. Usually, the amount of aluminum contained in the sulfuric acid solution is approximately l09/L. Mixing excessive Cl ions in the aluminum oxidation solution may also cause anodic oxidation of the aluminum alloy parts to cause spot corrosion and other failures.
5. Anodic oxide film is thin or red ash is hanging, and the corrosion resistance of the film layer is poor. The reasons for this failure are many, including the following aspects.
(1) Sulfuric acid content and operating conditions do not comply with the process specification. If the anodizing current density is low, the voltage is low, and the oxidation time is short, the oxide film formed on the surface of the aluminum alloy is relatively thin. If the concentration of the solution is low, the ions in the solution are small and the conductivity of the solution is small. To achieve the same current density, the solution of the low concentration solution has a higher cell voltage than the high concentration cell voltage, and the anodizing of the sulfuric acid is generally controlled by the voltage. Therefore, when the concentration of the solution is low, the current density is small at the specified voltage, and the resulting oxide film is also thin. When the temperature of the solution is low, the viscosity of the solution is large, the ion movement is slow, and the conductivity of the solution is small. Under the specified voltage, the current density is small, and the resulting oxide film is, of course, thin. On the contrary, the oxide film is thick, but the dissolution of the oxide film is also accelerated, and a loose powdery oxide film is formed.
(2) The parts are too loose, and the jig and the conductive rod are in poor contact. Checking the mounting condition of the aluminum alloy parts will reveal that the parts are too loosely clamped and the electrical conductivity is poor, which also causes the anodized film layer to become thin. In addition, the old oxide film on the jig is not removed, and the parts are clamped on the jig with a thin oxide film, which also causes poor conductivity. The oxide film formation rate becomes slow and the oxide film becomes thin.
(3) Anodizing solution contains too much copper and iron ions. Because the anodization process includes aluminum alloy surface dissolution and oxide film formation, such as some high-strength aluminum alloy materials, copper, manganese, iron, silicon and other elements, in the anodization process, copper and iron ions dissolved into the solution is possible With the increase of the use time of the anodizing solution, the content of copper ions in the solution will increase, which will affect the thickness of the oxide film or surface ash.
The measures to eliminate such failures are: strict control of the oxidation process specification; pay attention to the removal of the residual oxide film on the surface of the rack and ensure contact between the rack and the part. The problem of excessively high contents of copper and iron ions in the plating solution can be solved by increasing the area of ​​the cathode and applying a small current electrolytic treatment or renewing the oxidation solution.
6. Parts and fixtures in contact with the burn, parts of the local place there are electric shock burns This failure is caused by the aluminum alloy parts and the cathode contact short circuit, parts of the short-circuit caused by contact with each other. Therefore, it is necessary to strengthen the contact inspection between the anodized parts and the fixture. Before the fixture is used, it must be cleaned. It must be clamped with the parts to ensure that the parts conduct well. When placing parts in the oxidation tank, pay attention to the distance from the cathode to avoid contact. In addition, it is necessary to prevent parts from coming into contact with each other to cause a short circuit and increase the distance between parts.
7. There are black spots (black streaks) or reticulate foam patterns on the oxide film. The main causes of this failure are: After the parts are chemically deoiled, the light leakage process is oxidized and the water glass left on the parts forms silicic acid. As a result, the chemical degreasing fluid is not clean during heat treatment; there are oil stains or other contaminants on the surface of the parts; suspended impurities are contained in the oxidizing solution; plugging is performed after the oxidized parts are not washed; the surface of the solution has suspended impurities, copper and Too much iron impurities.
Excluding such failures requires thorough pretreatment; to strengthen the cleaning of oxidized parts, and to clean them immediately after oxidation, to avoid the treatment liquid or impurities remaining on the surface of the oxide film; to remove or renew the partial oxidation solution to reduce impurities in the solution.
8. Oxidized parts are easily filled with watermarks and watermarks after filling with hot water. The reasons for this breakdown of the oxide film after filling with potassium dichromate are as follows: the temperature of the filling and sealing solution is too low and the filling time is short; the pH value of the solution is not appropriate Blocking solution too much aluminum hydroxide, SO42- content is too high; anodizing temperature is too high to cause the oxide film is too thin, the film hole was open and so on.
Excluding such failures is mainly aimed at adjusting the pH value of the closed filling solution, strictly controlling the composition and process conditions of the solution, checking and correcting the contents of SO42- and aluminum hydroxide in the sealing solution, controlling the anodizing process conditions, and increasing the oxidation time.
9. After the anodic oxidation, the film will appear red or blue after dyeing. The main reasons for the red or blue dyeing of the film after oxidation are:
(1) The oxide film has poor adsorption performance. When the black oxide film was dyed with the acid black ATT dye, a reddish blue defect occurred. Acidic black ATT dyes are composed of 70% of acidic blue black lOB and 30% of acidic orange II molecular structure, so when the anodized film has small pores and poor absorption performance, the small molecule of acidic orange II is easily absorbed by the oxide film. The acid orange II in the film exceeds the dye ratio, so the color becomes red.
(2) The effect of the surface state of the sheet and extruded parts. Before the anodic oxidation, the parts should be alkali-etched to remove the surface crust to obtain a uniform black color. Otherwise, red or black flowers will also be obtained. For aluminum alloy parts with high silicon content, it can be immersed for about 20s in 40mL/L ~ 50mL/L nitric acid and about 10mL/L of hydrofluoric acid solution to dissolve impurities, leaving a thin layer of purer aluminum. In order to improve the performance of the anodized film, it has a good adsorption performance, and a uniform black color is obtained.
(3) Improper pH of the dyeing solution. The pH value of the dyeing solution has a great influence on the dyeing of the oxide film, because the absorption properties of the various dyes have their own different pH values. If the pH value is close to 7, the acid blue-black lOB has good adsorption performance, while the acidic orange II has poor adsorption performance, so the color is bluish. When the pH is about 4.5, the acid blue-black lOB has poor adsorption capacity and acidity. Orange II has a strong adsorption capacity, so the color is reddish.
The methods to eliminate this kind of failure include: strengthening the treatment before oxidation; appropriately prolonging the anodizing time, increasing the pores of the oxide film so that the large acid blue black 10B can be absorbed by the oxide film; controlling the pH of the dyeing solution, avoiding To open the value of 7 or 4.5, it is generally better to control about 3.6 or 5-6.