How to conduct quality inspection after anodizing process?

Quality Inspection Methods After Anodizing

Anodizing is a common metal surface treatment process, widely used for the surface treatment of aluminum and its alloys. To ensure that anodized products meet quality requirements, rigorous quality inspection is essential. The following are the main quality inspection methods and standards after anodizing.

I. Appearance Quality Inspection

1. Visual Inspection

Visual inspection is a basic and direct inspection method, primarily checking:

- Surface Color Uniformity: Observe the color consistency of the oxide film and any color variations.

- Surface Finish: Check the surface for smoothness and defects such as roughness and burrs.

- Surface Defects: Check for obvious defects such as scratches, spots, bubbles, flaking, and cracks.

- Surface Contamination: Check for contaminants such as oil, water stains, and dust.

2. Gloss Inspection

Use a gloss meter to measure surface gloss to ensure that it meets the required gloss standards. The typical measurement angle is 60°, though 20° or 85° can be used in special circumstances.

II. Film Thickness Measurement

1. Eddy Current Thickness Measurement

This method uses an eddy current thickness gauge to measure oxide film thickness. It is suitable for measuring non-conductive films on non-magnetic substrates. Notes on measurement:

- Calibrate the instrument using a standard sheet of the same substrate.

- Measure multiple points and average the results.

- Avoid measuring at edges or bends.

2. Metallographic Microscope Method

After cutting, mounting, grinding, and polishing the sample, the oxide film cross-section is observed using a metallographic microscope to directly measure the film thickness. This method is highly accurate but destructive.

3. Gravimetric Method

The average film thickness is calculated by measuring the weight change of the sample before and after oxidation, combining the oxide film density and area. The calculation formula is:

Film Thickness (μm) = (Weight Gain in mg) / (Area in cm² × Oxide Film Density in g/cm³) × 10

III. Corrosion Resistance Testing

1. Salt Spray Test

The sample is placed in a salt spray test chamber to simulate a marine atmosphere and evaluate the corrosion resistance of the oxide film. Commonly used standards:

- Neutral Salt Spray Test (NSS): 5% NaCl solution, pH 6.5-7.2, 35±2°C

- Acetic Acid Salt Spray Test (AASS): Add acetic acid to NSS, adjusting the pH to 3.1-3.3

- Copper Accelerated Acetic Acid Salt Spray Test (CASS): Add CuCl₂ to AASS

2. Spot Test

A specific chemical solution is dropped onto the oxide film surface and the time it takes for the solution to penetrate the oxide film to the substrate is measured to evaluate the film's density and corrosion resistance. A mixture of hydrochloric acid and potassium dichromate is commonly used.

IV. Hardness Testing

1. Microhardness Test

A microhardness tester is used to measure oxide film hardness. A typical load is 25-100g, and the hold time is 10-15 seconds. Notes on Measurement:

- Choose a flat surface

- Avoid measuring at edges or thin areas

- Measure multiple points and average the results

2. Pencil Hardness Test

Use a standard pencil to scratch the oxide film surface at a 45° angle. Observe the highest hardness grade without scratching to assess surface hardness.

5. Wear Resistance Test

1. Falling Sand Test

Allow standard sand particles to fall freely from a fixed height onto the oxide film surface. Measure the amount of sand required to abrade a unit area of ​​the oxide film to assess wear resistance.

2. Friction and Wear Test

Use a Taber abrader or reciprocating wear tester to measure the wear volume of the oxide film under a certain load and number of frictions.

6. Sealing Quality Test

1. Acid Immersion Test

Immerse the sample in an acidic solution. Measure the weight loss or observe surface changes before and after immersion to assess sealing quality.

2. Dye Test

Immerse the sample in a dye solution and observe the absorption of dye into the oxide film pores to assess sealing effectiveness. A completely sealed oxide film should not absorb dye.

VII. Electrical Performance Testing

1. Breakdown Voltage Test

Measure the voltage at which the oxide film breaks down under gradually increasing voltages to evaluate the film's insulation properties.

2. Insulation Resistance Test

Use a high resistance meter to measure the insulation resistance of the oxide film to evaluate its electrical insulation properties.

VIII. Adhesion Testing

1. Tape Peel Test

Apply a standard tape to the oxide film surface and quickly peel it off to observe whether the film falls off and to evaluate adhesion.

2. Bend Test

Bend the sample to a certain angle to observe whether the oxide film cracks or peels and to evaluate adhesion.

IX. Other Special Performance Testing

Depending on the product's intended use, the following tests may also be required:

- UV Aging Test: Evaluates the weather resistance of the oxide film

- Thermal Cycling Test: Evaluates the stability of the oxide film under temperature fluctuations

- Chemical Resistance Test: Evaluates the oxide film's resistance to specific chemicals

X. Testing Considerations

1. Sampling Representativeness: Select samples that represent the quality of the entire batch of products for testing.

2. Environmental Control: Some tests require standard temperature and humidity conditions.

3. Instrument Calibration: Regularly calibrate testing instruments to ensure measurement accuracy.

4. Standard Compliance: Tests must strictly adhere to relevant national or industry standards.

5. Complete Records: Detailed documentation of test conditions, methods, and results is maintained for traceability and analysis.

Through these comprehensive quality tests, we ensure that anodized products meet all performance requirements, providing reliable assurance for subsequent use. Products for different applications can select appropriate testing items based on their specific needs, ensuring quality while minimizing testing costs.