How to perform quality inspection after anodizing?

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, strict 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 the basic and direct inspection method, mainly checking:

- Surface color uniformity: Observe whether the oxide film color is consistent and whether there is any color difference.

- Surface smoothness: Check whether the surface is smooth and whether there are any defects such as roughness or burrs.

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

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

2. Gloss Measurement

Use a gloss meter to measure the surface gloss to ensure it meets the product's required gloss standards. The measurement angle is usually 60°, but 20° or 85° can be used in special cases.

II. Film Thickness Measurement

1. Eddy Current Thickness Measurement

Eddy current thickness gauges are used to measure oxide film thickness. This method is suitable for measuring non-conductive films on non-magnetic substrates. Points to note during measurement:

- Use a standard sheet of the same substrate for instrument calibration.

- Take multiple measurements and average the results.

- Avoid measuring at edges or bends.

2. Metallographic Microscopy

After cutting, mounting, grinding, and polishing the sample, the cross-section of the oxide film 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, combined with the oxide film density and area. The calculation formula is:

Film thickness (μm) = (weight gain mg) / (area cm² × oxide film density g/cm³) × 10

III. Corrosion Resistance Testing

1. Salt Spray Test

Samples are placed in a salt spray test chamber to simulate a marine atmospheric environment and evaluate the corrosion resistance of the oxide film. Common Standards:

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

- Acetic Acid Spray Test (AASS): Adjust pH to 3.1-3.3 by adding acetic acid to the NSS test.

- Copper Accelerated Acetic Acid Spray Test (CASS): Add CuCl₂ to the AASS test.

2. Drop 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 density and corrosion resistance of the oxide film. A commonly used solution is a mixture of hydrochloric acid and potassium dichromate.

IV. Hardness Testing

1. Microhardness Test

The hardness of the oxide film is measured using a microhardness tester. Common loads are 25-100g, and the holding time is 10-15 seconds. Precautions during measurement:

- Choose a flat surface

- Avoid measuring at edges or thin areas

- Take the average of multiple measurements

2. Pencil Hardness Test

Use a standard pencil to scratch the oxide film surface at a 45° angle. Observe the high hardness level (no scratches) to assess surface hardness.

V. Abrasion Resistance Test

1. Drop Test

Let standard sand grains fall freely from a fixed height to impact the oxide film surface. Measure the amount of sand required to wear down a unit area of ​​the oxide film to assess abrasion resistance.

2. Friction and Wear Test

Use a Taber abrasion tester or a reciprocating abrasion tester to measure the wear of the oxide film under a certain load and number of friction cycles.

VI. Sealing Quality Inspection

1. Acid Immersion Test

Immerse the sample in an acidic solution. Assess sealing quality by measuring the weight loss before and after immersion or observing surface changes.

2. Dyeing Test

Immerse the sample in a dyeing solution. Observe the adsorption of dye into the oxide film pores to assess the sealing effect. A fully sealed oxide film should not adsorb dyes.

VII. Electrical Performance Testing

1. Breakdown Voltage Test

Measure the breakdown voltage of the oxide film under gradually increasing voltage to evaluate its insulation performance.

2. Insulation Resistance Test

Measure the insulation resistance of the oxide film using a high-resistance meter to evaluate its electrical insulation performance.

VIII. Adhesion Testing

1. Tape Peel Test

Apply standard adhesive tape to the oxide film surface and then quickly peel it off. Observe whether the oxide film detaches to evaluate adhesion.

2. Bending Test

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

IX. Other Special Performance Tests

Depending on the product application, the following tests may also be required:

- UV Aging Test: To assess the weather resistance of the oxide film.

- Thermal Cycling Test: To assess the stability of the oxide film under temperature changes.

- Chemical Reagent Resistance Test: To assess the oxide film's resistance to specific chemicals.

X. Testing Precautions

1. Sampling Representativeness: Samples representative of the entire batch of products should be selected for testing.

2. Environmental Control: Some tests need to be conducted under standard temperature and humidity conditions.

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

4. Standard Compliance: Strictly adhere to relevant national or industry standards during testing.

5. Complete Records: Record testing conditions, methods, and results in detail for traceability and analysis.

Through the above comprehensive quality testing, it can be ensured that anodized products meet various performance requirements, providing reliable assurance for subsequent use. Different products for different applications can select appropriate testing items according to actual needs, optimizing testing costs while ensuring quality.