Types of aluminum alloy anodic oxidation defects

Foreword

1. In oxidation production process of aluminum and aluminum alloys, various defects can be mainly divided into three categories, namely, surface defects of oxidation surface treatment products, shape and size defects of oxidation surface treatment products, appearance and performance defects of oxidation surface treatment products.
2. Oxidation surface treatment products have the most surface defects in production site, and scrap rate is also the highest. The most important ones are fingerprint corrosion, scratches, adhesion, coarse sand, light sand, poor degreasing, oxidation bubbles, unclean film removal, snowflake corrosion, oxidation white spots, electric injury, slag inclusion, oxide film peeling, pitting, burst film, color sealing, pinhole corrosion, color difference, acid and alkali water corrosion, sealing dust, no paint film, pitting, electrophoretic bubbles, pulverization of oxide film, etc.
3. Size defects of oxidation surface treatment products account for a small percentage of rejects in production, mainly including reworked wall thickness, excessive thread marks, etc.
4. Appearance and performance defects of oxidation surface treatment products mainly include unqualified hole sealing, substandard oxide film thickness, substandard pencil hardness of paint film, substandard corrosion resistance of paint film, etc.
5. Following is a comprehensive description of names of various defects, causes, definitions, characteristics and countermeasures in the form of a list, which can be used as a reference for work and study by technical personnel, production personnel, and quality inspection personnel.

1. Surface defects of aluminum and aluminum alloy products with oxidized surface treatment

Surface defects of products with oxidized surface treatment are the most common in production sites, and scrap rate is also the highest. Main defects are fingerprint corrosion, scratches, adhesion, coarse sand, light sand, poor degreasing, oxidation bubbles, incomplete film stripping, snowflake corrosion, oxidation white spots, electrical injuries, slag inclusions, oxide film peeling, pitting, film explosion, sealing color, pinhole corrosion, color difference, acid and alkali water corrosion, sealing gray, no paint film, pitting, electrophoresis bubbles, oxide film powdering, etc.
Q001 Fingerprint-like corrosion

Definition	Fingerprint or glove stain
Cause	Operation
Features	Surface of aluminum without surface treatment reacts with substances such as sodium chloride and lactic acid in human sweat, resulting corrosion marks are called fingerprint corrosion, the most common being pitting corrosion in the shape of fingerprints
Appearance	Handprint Corrosion
Causes	Causes: 1. Sawing during extrusion process, and gloves used by workers when loading the baskets are relatively dirty, leaving stains after contact with surface of profile, and surface stains on profile cannot be removed by oxidation after aging; 2. During process of oxidation and rowing, worker's gloves have been used for too long, especially when they are stuck with oil and leave their fingerprints at the end of profile. After oxidation, fingerprints are pitting corrosion; 3. After upper row, parking time is too long without oxidation treatment; 4. Before oxidation Handling degreasing is not complete.
Countermeasures	1. Try to pay attention to cleanliness of gloves during extrusion process and upper row, replace dirty and wet gloves in time; 2. After oxidation and upper row, profiles should not be placed for more than 6 hours; 3. Extend degreasing time.

Q002 Scratch

Definition	Damaged and scratched profile surface
Cause	Operation
Features	It has thin and long lines or point scars, with shimmering luster, and various shapes. Continuous scars are usually called handling scars. Sometimes improper packaging can also cause scars during transportation.
Appearance	Scratched
Causes	Bumps between materials, improper operation or collisions between materials and frames, etc.
Countermeasures	1. Upper row should be handled with care, and it is strictly forbidden to collide with material when lifting material; 2. Edge of material frame must be covered with a protective rubber sleeve; 3. No more than 6 rows of materials can be lifted each time, and profiles with different lengths are placed separately; 4. Do not use damaged pads in the lower row process, and do not collide brutally.

Q003 Crossing overlapping

Definition	Materials overlap during oxidation or electrophoresis, and film is abnormally formed due to abnormal proximity
Cause	Operation
Features	Imprint of laminated profile can be seen from part where film is not formed and part where end is thinned, and sometimes a part of rainbow (interference color) can be seen.
Appearance	Adhesion
Causes	1.Gap between bars is too dense, resulting in abnormal contact; 2. Insufficient binding strength, aluminum wire or fixtures loosen during washing process, causing profile to slide up and down on row rod, resulting in materials being connected together through alkali etching, acid etching, oxidation, and electrophoresis treatment.
Countermeasures	1. Adopt correct binding method, tie three aluminum wires (two for small material) with electrophoretic material, and keep a distance of 2-3 fingers between upper and lower profiles; 2. Profiles with a large drop in the middle must be tied to the center line according to order requirements; 3. Slope of the lower groove increases, and exhaust process of electrophoresis tank should be slow, so as to avoid adhesion between profiles caused by violent shaking.

Q004 Rough etching

Definition	Surface roughness of aluminum due to excessive alkali corrosion
Cause	Operation
Features	Due to excessive erosion, surface is rough and dull, and in severe cases, dimensional accuracy is affected due to dissolution of profile
Appearance	Coarse sand
Causes	1. Temperature of alkali tank is too high; 2. Alkali concentration is too high; 3. Concentration of aluminum ions in alkali tank is too low; 4. Alkali etching time is too long; 5. Alkali tank liquid is polluted; 6. There are many times of rework.
Countermeasures	1. Adjust conditions of bath solution (sodium hydroxide concentration, dissolved aluminum ion content, temperature); 2. Adjust treatment time; 3. Regularly clean tank slag and adjust bath solution; 4. Reduce number of repeated treatments.

Q005 Insufficient etching

Definition	In alkaline etching process of aluminum materials, due to insufficient etching, effect of eliminating surface defects fails to achieve expected goal.
Cause	Alkali etching process
Features	Surface has no sand effect or does not meet customer requirements
Appearance	Light sand
Causes	1. Temperature of alkali tank is too low; 2. Alkali etching time is too short; 3. Alkali concentration is too low; 4. Concentration of aluminum ions in alkali tank is too high.
Countermeasures	1. Pay attention to controlling temperature and concentration of alkali tank; 2. Prolong alkali etching time appropriately; 3. Reasonably adjust concentration of aluminum ions.

Q006 Uneven degreasing

Definition	Uneven alkali etching due to incomplete degreasing
Cause	Degreasing process
Features	Surface of aluminum material is unevenly etched due to incomplete degreasing, surface of aluminum material has different gloss after anodizing, and surface color is uneven or there are stains after coloring
Appearance	Poor degreasing
Causes	1. Insufficient degreasing time; 2. Insufficient active ingredients in degreasing tank liquid; 3. Serious oil pollution on the surface of workpiece.
Countermeasures	1. Add degreasing agent; 2. Extend soaking time ≥ 3 minutes; 3. Workpieces with serious surface oil pollution need to be pretreated by manual wiping.

Q007 Bubble (anodic oxide)

Definition	Gas generated during electrolysis or air used for stirring stays in gaps or corners of material, so no oxide film can be formed, and usually it will not be colored.
Cause	Anodizing, handling
Features	In gaps or corners of material, film is partially thin or absent, and there are traces of air bubbles remaining on the surface of anodized film. If electrolytic coloring is performed, uniform color cannot be obtained.
Appearance	Oxidized bubbles
Causes	1. Improper lifting angle; 2. Speed of entering tank is too fast; 3. Shape of aluminum material is not conducive to removal of gas; 4. Defoaming bag is damaged.
Countermeasures	1. By controlling slope of lower tank; 2. Prolonging presoaking time; 3. Damaged defoaming bag should be replaced in time.

Q008 Peel off net

Definition	Anodized film is not completely removed
Cause	Alkali etching process
Features	This phenomenon occurs in reworked profile. Since old oxide film is not removed during rework, a new oxide film cannot be formed in this area during re-oxidation, and a concave-convex peeling layer will appear at this time
Appearance	Difficult to remove film
Causes	1. Reworked stripped profiles were soaked in sulfuric acid soaking tank for insufficient time; 2. Alkaline etching stripped for insufficient time.
Countermeasures	1. Prolong immersion time in sulfuric acid solution; 2. Prolong alkali etching time.

Q009 snowflake corrosion

Definition	Pitting corrosion in water washing caused by impurities contained in material
Cause	Casting, Oxidation Process, Operation
Features	Shaped like a snowflake, center of spot has a black spot as core, and spreads out many claws around, like an octopus in sea
Appearance	Snowflake corrosion
Causes	1. Extruded profile contains a small amount of zinc or gallium, which reacts with Cl- or F- ions in water washing tank after neutralization treatment process; 2. After blank is neutralized, it stays in water tank for too long; 3. Sink is contaminated.
Countermeasures	1. Monitor production process of aluminum rods and control content of zinc or gallium; 2. Control speed of making materials to ensure that blanks do not soak for more than 10 minutes; 3. Concentration of nitric acid in neutralization tank is ≥ 5% (5%- 8%); 4. Increase drainage to ensure cleanliness of sink.

Q010 White color

Definition	In the absence of peeling of oxide film, white dots or dots of uncolored traces on the surface of aluminum material
Cause	Casting, extrusion, oxidation process
Features	Different from "peeling", white spot-like defects appear along with peeling. White dots are cracks generated on film, normal film has not yet formed, its peripheral part is not colored, it occurs more along extrusion direction, and it feels handy when touched.
Appearance	Oxidized white spots
Causes	1. There are inclusions in alloy, which makes oxide film discontinuous; 2. Alkaline fog is attached to oxide film.
Countermeasures	1. Strictly control casting process; 2. Arrange oxidation of workpiece as soon as possible after upper row; 3. Improve ventilation facilities of workshop.

Q011 Electrical burning

Definition	During anodizing treatment, current density is locally excessive, resulting in a burnt appearance or electrical breakdown
Cause	Anodizing, handling
Features	There are burning marks on oxide film, generally black or yellow, and profile breakdown in severe cases.
Appearance	Electric injury
Causes	1. Excessive oxidation current density; 2. Short circuit in contact between aluminum material and cathode plate; 3. Poor contact between aluminum material and fixture; 4. Current rises too fast during anodizing; 5. Cathode is damaged and area is too small;
Countermeasures	1. Oxidation current density should not be too large, and current density should be controlled between 1.2-1.5mA/dm2; 2. Electrode spacing should be well controlled when lowering tank, and it is strictly forbidden for profile to touch cathode plate; 3. Upper row of rods should be polished well, screws on rack must be tightened, and material head must be tightened when clamping material; 4. Current soft rise time setting must meet requirements; 5. Replace damaged cathode plate in time.

Q012 Slag

Definition	Extrusion, casting, mold
Cause	There are non-metallic inclusions in metal structure, visible to naked eye in low-magnification samples, and surface of metal product will be exposed after oxidation treatment, visible to naked eye or felt by touching product
Features	Generally, it appears as a broken line and is consistent with extrusion direction. It is invisible after extrusion, but visible after oxidation treatment
Appearance	Slag
Causes	1. Extrusion cylinder and extrusion rod are not aligned, so that surface layer of ingot or foreign matter on inner wall of extrusion cylinder are involved and appear on the surface of extruded profile; 2. Because position of die hole is too close to outer circle during mold design.
Countermeasures	1. Make die hole located in the center of die as far as possible in mold design; for hollow profiles, circumscribed circle of split hole should be reduced; 2. Always check alignment of extrusion cylinder and extrusion rod and adjust it in time , leaving more residual pressure; 3. Remove foreign matter on inner wall of extrusion cylinder and fixed extrusion pad; 4. Reduce temperature of extrusion pad to avoid excessive lubrication; 5. Increase temperature of extrusion cylinder and billet.

Q013 Spalling

Definition	When colored, oxide film peels off in a half-point shape, resulting in uncolored spots
Cause	Anodic oxidation, coloring
Features	White dots or lumps are irregularly distributed on the surface of profile, and there is no hand feeling when touched.
Appearance	Oxide film peeled off
Causes	1. Coloring voltage is too high or coloring time is too long; 2. Coloring solution is polluted; 3. Barrier film formed during oxidation is too thin or uneven.
Countermeasures	1. Correct coloring conditions; 2. Remove impurities; 3. Increase oxidation voltage.

Q014 Black spots

Definition	Black star-shaped corrosion pits produced on the surface of aluminum
Cause	Anodizing
Features	Irregular distribution of black dots, no oxide film at the location of corrosion point
Appearance	Black spots
Causes	Concentration of chloride ions in oxidation electrolyte is too high.
Countermeasures	Replace bath to ensure stability of oxidation bath.

Q015 Pinhole

Definition	Due to large difference in thermal expansion coefficient between oxide film and aluminum substrate, phenomenon of cracking and damage of oxide film under external force or high temperature
Cause	Anodizing, Operation
Features	When observed in a direction oblique to surface under strong light, distribution of flaky scales can be seen.
Appearance	Burst film
Causes	1. Sealing time is too long; 2. High film material is not stirred by air; heat is not exchanged in time; 3. Lower row is brutally operated, profile is subjected to excessive force, and oxide film cracks.
Countermeasures	1. Adjust sealing time; 2. Ventilate and stir when high film material is oxidized; 3. Standardize lower row operation.

Q016 Iridescence

Definition	Also called iridescent film or interference film, it is a phenomenon of light interference, which means that there is a layer of surface film
Cause	Sealing
Features	Visible iridescent colors when viewed obliquely to the surface
Appearance	Sealed and colored
Causes	1. In heat sealing, due to existence of silicon dioxide and phosphate, sealing is poor; 2. In cold sealing, due to high concentration of sealing bath solution or high temperature of bath, sealing time is too long, etc. Resulting in over-sealing; 3. Poor anodic oxidation and electrolysis; 4. Corrosion of sealing film
Countermeasures	1. Adjust composition of bath solution; 2. Properly reduce temperature of bath solution and reduce sealing time; 3. Reduce nickel ion content in sealing tank; 4. Regularly clean bath slag and filter bath solution frequently to keep bath solution clear.

Q017 Pinhole pitting corrosion

Definition
Cause	Degreasing, electrophoresis
Features	Irregularly arranged, small hole-like depressions or perforations on the surface of paint film. When viewed along direction inclined to the surface, pinholes of paint film are more clear.
Appearance	Pinhole Corrosion
Causes	1. When aluminum material enters electrophoresis tank, air bubbles or air on the surface of paint liquid are involved; 2. Air is involved in circulation system; 3. Cathode shielding is poor or defoaming bag is damaged, and there are fine air bubbles in paint liquid ; 4. Electrophoretic voltage is too high, and electrolytic reaction is violent, resulting in bubbles; 5. Impurities mixed in electrophoretic paint adhere to paint film; 6. Temperature of electrophoretic bath is too high; 7. Low and excess solvent will lower polarization ability of paint film, resulting in weakened resistance to impurities; 8. Pre-treatment degreasing is not clean; 9. Blank is left for too long
Countermeasures	1. Lower tank must have a slope and shake up and down a few times; 2. Check operation of equipment frequently; 3. Replace defoaming bag; 4. Reduce electrophoresis voltage; 5. Regularly replace filter bag; 6. Control temperature of electrophoresis tank within the process range; 7. Adjust process parameters of bath solution to normal range; 8. Increase degreasing intensity of pre-treatment, add nitric acid regularly, and increase passivation intensity.

Q018 Chromatic aberration

Definition	A visual difference in color
Cause	Coloring, operation
Features	Color of aluminum material after oxidation coloring is different from that of standard plate
Appearance	Color difference
Causes	1. Poor electrical conductivity; 2. Clamp material is not tight; 3. Inaccurate coloring and color matching.
Countermeasures	1. Water chestnut of conductive rod should be polished until color of matrix is exposed; 2. Clamp material should be clamped tightly to prevent loosening; 3. Colorist strictly matches color according to standard color board, and corrects it in time if there is any deviation.

Q019 Acid slobbery stain

Definition	Surface of profile is corroded by acid and alkaline water
Cause	Operation
Features	There are white flow marks or round spots on the surface of profile
Appearance	Acid and alkali water corrosion
Causes	1. Acid and alkali solutions attached to fixture or rack are not thoroughly cleaned in subsequent washing process and flow to the surface of aluminum material; 2. There is acid and alkali solution that has not been cleaned off surface of aluminum material; 3 .After hole sealing is completed, when seasoning, it will cross other material racks from the draining area.
Countermeasures	1. Thoroughly clean jig and material rack; 2. Clean small inner cavity profiles multiple times; 3. Do not cross from other material racks; 4. Ensure that process parameters of each washing tank meet production requirements; 5. Rinse conductive girder with a water pipe when lowering oxidation tank.

Q020 Sealing smut

Definition	A layer of calcification is attached to the surface of profile after sealing
Cause	Sealing
Features	Surface of oxidized profile is attached with erasable white ash, and surface of colored profile is attached with yellow ash that is not easy to wipe off
Appearance	Sealed hole dust
Causes	1. Calcium or magnesium ions in the water of sealing tank are too high; 2. Turbidity in sealing tank is adsorbed to surface of aluminum material, which is not washed away in subsequent washing process; 3. Sealing time is too long; 4. Sealing solution is aging.
Countermeasures	1. Ensure cleanliness of washing tank after sealing; 2. Increase filtration of sealing tank solution to reduce precipitation; 3. Grasp sealing time; 4. Prepare a new tank solution.

Q021 Film-free

Definition	When electrophoretic coating is applied, aluminum profile is not coated with an organic paint film
Cause	Electrophoresis, operation
Features	Surface has a lower brightness than the profile with a paint film, handle feels rough and sticky
Appearance	No paint film
Causes	1. Poor electrical conductivity; 2. Too long soaking time in RO1 and RO2 washing tanks; 3. Too high solvent content in washing tank; 4. High pH value of electrophoresis tank; 5. Too high temperature in hot water tank and long soaking time , pores of oxide film are closed.
Countermeasures	1. Check whether wiring and tie-up are firm; 2. Strictly control soaking time of washing tank (2-3 minutes); 3. According to process requirements, control content of the solvent; 4. Check pH value of bath frequently, and refine it in time if it is high; 5. Strictly control hot water tank process.

Q022 Dust stain

Definition	Fine granular foreign matter formed by foreign matter such as dust attached to the surface of paint film or under paint film.
Cause	Electrophoresis
Features	Dots are randomly distributed on the surface of profile, and there is a raised feeling when touched by hand.
Appearance	Pitting
Causes	1. Washing tank before electrophoretic painting process is not clean or conductivity is too high; 2. There are relatively large mechanical impurities in electrophoretic tank; 3. Floating objects such as dust in workshop air fall to drain 4. There are dust and other impurities in curing furnace.
Countermeasures	1. Change water in washing tank and check water quality regularly; 2. Strengthen filtration frequency of electrophoresis tank liquid and replace filter bag; 3. Electrophoresis workshop must have an independent air circulation system and clean it every day; 4. Regularly clean curing furnace , clean or replace hot air circulation filter.

Q023 Bubble(film)

Definition	Bubble marks on the surface of a profile due to bubble attachment
Cause	Electrophoresis, operation
Features	Generally irregular circular bubble traces, varying in size
Appearance	Electrophoretic paint film
Causes	1. When aluminum material is immersed in electrophoresis tank, air bubbles or air on the surface of paint liquid are involved; 2. Paint liquid contains tiny bubbles; 3. There are too many bubbles on the surface of aluminum material, paint liquid has poor fluidity and cannot be brought out; 4. Inclination angle of aluminum material is not enough during process of entering tank; 5. Valve of paint solution is not closed tightly, and air is sucked in; 6. Content of solvent A in tank solution is low.
Countermeasures	1. Increase slope of the lower groove of profile, slowly lower groove, and then stand still for 30 seconds before electrophoresis; 2. Check whether defoaming bag is damaged; 3. Add a certain amount of solvent B or increase circulation amount; 4. Check closing of valve every time after drawing paint liquid; 5. Add solvent A in proper amount.

Q024 Pwodreing(JIS)

Definition	After anodizing, white powder is formed on the surface of film
Cause	Electrophoresis, anodic oxidation
Features	After anodizing, film is white powder and opaque; powder can be easily wiped off by hand.
Appearance	Pulverized oxide film
Causes	1. Temperature of electrolyte is too high; 2. Concentration of aluminum ions is too high; 3. Current density is too high; 4. Oxidation time is too long; 5. Immersion time after oxidation is too long; 6. Oxidation tank solution is not stirred sufficiently ; 7. Partial hanging material is too dense.
Countermeasures	1. Adjust temperature of bath solution; 2. Frequently separate excess aluminum ions; 3. Use appropriate current density; 4. Grasp oxidation time; 5. Control impregnation time; 6. Fully ventilate and stir when anodizing; 7. Control distance between upper row when upper row is arranged.

Q025 Yellowing (combined anodic oxide film)

Definition	Phenomenon that paint film or oxide film appears yellow
Cause	Anodic oxidation, electrophoresis
Features	Profile composite film looks yellow as a whole
Appearance
Causes	1. Coating is too thick; 2. Curing temperature is too high or curing time is too long; 3. Electrophoresis tank is polluted; 4. Quality of electrophoretic paint is abnormal; 5. Soaking time in water tank after oxidation is too long, resulting in yellowing of oxide film, and product is yellowing due to transparency of paint film;
Countermeasures	1. Improve painting conditions and reduce coating thickness; 2. Adjust furnace temperature to range required by process; 3. Refining electrophoretic tank solution; 4. Purchasing electrophoretic paint with stable quality and regularly sampling quality stability; 5. Controlling water quality and washing time of washing water after oxidation.

Q026 Gel adhesion(Dull color)

Definition	After electrophoretic profile is cured, granular electrophoretic paint is attached to the surface of profile.
Cause	Electrophoresis
Features	Generally, it is irregularly distributed on the surface of profile, and attached particles vary in size.
Appearance
Causes	1. Electrophoresis main tank and RO washing tank have not been cleaned for a long time, and solidified old paint is attached to tank wall, which is scratched and attached to profiles during production; 2. Acid is mixed into electrophoresis main tank or RO washing tank, coating resin is partially coagulated and adhered to profile; 3. Stirring is not uniform and emulsification is not complete when adding paint liquid to electrophoresis main tank.
Countermeasures	1. Regularly clean electrophoresis main tank and RO washing tank to reduce old paint attached to tank; 2. Prevent acid from being mixed into electrophoresis main tank and RO washing tank; 3. Stir for at least 30 minutes when adding paint solution to electrophoresis main tank, and pump it into main tank after emulsification is complete.

Q027 Acid slobbery stain (film)

Definition	After electrophoretic profile is cured, there are paint spots or paint flow marks on the surface of profile.
Cause	Electrophoresis
Features	There are irregularly distributed paint spots or paint flow marks on the surface of paint film.
Appearance	Paint marks
Causes	1. Residence time after electrophoresis is too long; 2. Concentration of paint is improper; 3. Washing after electrophoresis is insufficient; 4. Solid content of RO2 washing tank is too high; 5. Acid-base water drips from conductive beam.
Countermeasures	1. Residence time after electrophoresis tank is opened is within 1 min; 2. Coating concentration is strictly controlled according to process requirements; 3. Washing time after electrophoresis is appropriately extended; 4. Solid content of RO2 washing tank is reduced; 5. Oxidation process should fully spray water to wash girder.

Q028 Water spots

Definition	Also known as watermark, before or during curing, spot-like or water-drop-like pattern produced by adhesion of water droplets on the surface of paint film (especially surface of paint film on horizontal or inclined part).
Cause	Electrophoresis, operation
Features	It is easy to occur on upper part of horizontal part or inclined part, distribution is irregular, and its shape is a spotted or drop-shaped pattern.
Appearance
Causes	1. Water droplets attached to the surface of semi-dry paint film, resulting in changes in gloss during curing; 2. Impurities in water droplets attached to the surface of paint film cause changes in gloss or color; 3. Water quality of previous hot pure water washing is unqualified or soaking time is short.
Countermeasures	1. Extend draining time; 2. Ensure water quality of hot water tank and soaking time should be sufficient.

Q029 Bubble (colored)

Definition	Gas generated during electrolytic coloring or air used for stirring stays in gaps or corners of material and covers oxide film layer so that colored metal ions cannot enter pores of oxide film and form bubble-like stains.
Cause	Extrusion, anodizing, handling
Features	In gaps or corners of material, film is partially thin or absent, and there are traces of air bubbles remaining on the surface of anodized film. If electrolytic coloring is performed, uniform color cannot be obtained.
Appearance	Colored bubbles
Causes	Improper hoisting angle; too fast entry into tank; shape of aluminum material is not conducive to removal of gas; defoaming bag is damaged.
Countermeasures	By controlling slope of lower tank; prolonging presoaking time; damaged defoaming bags should be replaced in time.

2. Defects in appearance and performance of oxidation surface treatment products

Appearance and performance defects of oxidation surface treatment products mainly include unqualified hole sealing, substandard oxide film thickness, substandard pencil hardness of paint film, substandard corrosion resistance of paint film, etc. Under normal circumstances, once such defects are produced, they are often scrapped in batches, causing heavy losses, and must be prevented from time to time.
Q030 Sealing failure

Definition	Weight loss of sealing hole does not meet requirements of GB/T5237.2
Cause	Sealing
Features	Quality of sealing hole did not reach expected effect, and spot was dyed with a water-based pen on site, which cannot be wiped off after drying
Appearance	Unqualified hole sealing
Causes	1. Insufficient sealing time; 2. Low sealing temperature; 3. PH value of bath solution is not within process range; 4. Oxide film thickness exceeds specified film thickness seriously.
Countermeasures	1. Extend sealing time; 2. Adjust sealing temperature; 3. Adjust bath parameters to process range; 4. Measure oxide film thickness, and determine sealing time according to actual film thickness.

Q031 Oxide film thickness is not up to standard

Definition	Oxide film thickness does not meet requirements
Cause	Anodic oxidation
Features	Thickness of oxide film obtained after anodic oxidation cannot meet customer's requirements; or seriously exceed customer's requirements. At this time, although customer can accept it, increase in oxidation cost is not advisable;
Appearance	Oxide film thickness is not up to standard
Causes	1. Inaccurate calculation of oxidation time; 2. Output current of silicon machine does not match setting; 3. Tie-up is loose.
Countermeasures	1. Strictly follow calculation of suitable time for oxidation; 2. Check actual output value of current of silicon oxide machine frequently, so as to facilitate timely adjustment of oxidation time in production;

Q032 Pencil hardness is not qualified

Definition	Pencil hardness of profile electrophoretic paint film <3H
Cause	Electrophoresis
Features	Use a blade to cut off a part of paint film, grind it by hand to form flakes or rolls, and paint film is poorly pulverized
Appearance
Causes	1. Water temperature of hot water tank is low, which does not meet process requirements; 2. Curing temperature and time do not meet lower limit of process requirements; 3. Oxidation film is closed after soaking in hot water for a long time; 4. Bath solution is aging; 5. Combination ratio of hard monomer and soft monomer in original paint does not meet requirements.
Countermeasures	1. Keep temperature of hot water tank within process range; 2. Adjust temperature and curing time of curing furnace to within process range; 3. Control soaking time of hot water tank at about 6 minutes; 4. Replace part of tank solution; 5. Adjust combination ratio of hard monomer and soft monomer in original paint..

Q033 Corrosion resistance is not qualified

Definition	Corrosion resistance monitoring of paint film does not meet requirements of GB/T5237.3
Cause	Electrophoresis
Features
Appearance
Causes	1. Thickness of paint film does not meet requirements of national standard; 2. Hot water tank and pure water tank are polluted; 3. Acid value of bath solution is too high;
Countermeasures	1. Frequently check thickness of paint film to ensure that thickness of paint film meets requirements of national standard; 2. Frequently replace filter bags of hot water tank and pure water tank, regularly check Ph value of bath solution, and replace part of bath solution in time if it exceeds process range; 3. Refine tower C several times to adjust acid value within normal process range.

3. Dimensional accuracy of oxidation surface treatment products

Oxidation surface treatment has a low impact on product size, and there are few such defects, which often flow in from previous process. Impact of this process is mainly concentrated on two defects of excessive thread marks and reworked wall thickness.

Q034 Holding device impression

Definition	Tie mark exceeds drawing requirements
Cause	Operation
Features	During surface treatment, due to contact between aluminum material and hanger, impression produced by surface treatment of this part is affected. This mark is inevitable, but length cannot exceed customer's limit, otherwise it is unqualified.
Appearance	Tie marks
Causes	1. Inaccurate positioning of conductive rods during upper row; 2. Upper row is loosened, which causes profile to move up and down during pre-processing; 3. Angle of row and the angle of lower groove are insufficient. 4. Specifications of conductive rod do not meet process requirements
Countermeasures	1. Determine distance between conductive rods when upper row is arranged, upper and lower rows must be consistent. For workpieces with special requirements, special conductive rods and fixtures are used; 2. Aluminum wires used for upper row must be strong and profiles must not be loose. Upper row of fixtures must be used to ensure that profiles cannot slide up and down; 3. Arrange from bottom hole of conductive rod to ensure that both ends have a sufficient angle of inclination, and angle is required to be greater than 30° when going down groove; 4. Conductive rods must meet requirements of "Operation Specifications for Conductive Rods in Oxidation Workshops", and those that do not meet requirements must be replaced in time.

Q034 Lack of wall thickness

Definition	Wall thickness of reworked product is lower than customer's requirement
Cause	Operation
Features	It often occurs in repeated reworked products, and wall thickness measurement is lower than lower limit required by customers.
Appearance
Causes	1. Size of extrusion material is unqualified; 2. Oxidation process has been reworked many times.
Countermeasures	1. Strengthen inspection of incoming materials in upper row; 2. Try to make finished products successfully at one time.

Gud Mould Industry Co., Ltd