Failure analysis of coating / coating

Date：2022-03-09 13:25:00Views：835

Overview of coating / coating materials

Coating / plating can not only decorate the appearance of parts and repair the surface defects of parts, but also give special properties to the surface of parts, including improving surface hardness, wear resistance, corrosion resistance, conductivity and high-temperature oxidation resistance. The products involved include household appliances, automobiles, doors and windows, metal fasteners and electronic products. Due to the new requirements of technology and the high requirements of products, and customers' different understanding of high-demand products and processes, failures such as delamination, cracking, corrosion and discoloration of coating / coating materials occur frequently, which often leads to responsibility disputes between suppliers and users, resulting in serious economic losses. Through a series of analysis and verification means of failure analysis, the root cause and mechanism of failure can be found, which is of great significance in improving product quality, process improvement and responsibility arbitration.

Coating / coating material service group

Coating / coating material manufacturers: identify their product quality problems, go deep into the design, production, process, storage, transportation and other stages of possible causes of product failure, and deeply study the root causes and mechanism of failure, so as to provide basis for improving product yield and optimizing production process.

Dealers or agents: control the quality of incoming materials and provide favorable evidence for quality responsibility.

Machine users: follow up the product reliability in time to improve the core competitiveness of products.

Coating / coating failure analysis steps

① Background check:

Failure background (failure overview, defect rate, service conditions (stress status and environmental description, etc.), design life and actual life (applicable to fracture failure), process flow (detailed description of production process flow), product material specification (mechanical properties, composition, hardness specification and other parameters)

② Propose analysis scheme:

I. appearance inspection: microstructure observation (metallographic structure, inclusion analysis, carbide non-uniformity, coarse-grained layer, decarburized layer and other defect analysis);

II. Non destructive analysis: C-sam ultrasonic scanning, X-ray coating thickness analysis, etc;

III. destructive analysis: slice analysis, SEM / EDS composition analysis, red ink test and other technical analysis.

③ Preliminary conclusion: the preliminary failure conclusion is obtained by integrating various analysis methods such as physics and chemistry;

④ Verification: design simulation test to reproduce the failure phenomenon and verify the preliminary conclusion;

⑤ Report: make a comprehensive failure analysis report according to the test results, find out the failure causes and put forward corresponding improvement suggestions.

Main failure modes (but not limited to)

Delamination, cracking, corrosion, blistering, coating / coating falling off, discoloration failure, IC delamination failure, multilayer ink falling off failure, coating sample interface point corrosion failure, coating surface blistering failure;

(1) Possible causes of paint coating falling off

1. The surface of the coated workpiece is too smooth, the surface is not treated or not treated thoroughly before painting, and there is residual water, oil stain, oxide scale, etc. on the surface;

2. Incorrect primer selection causes paint falling off. For example, the paint film is too hard, which makes it difficult for the top coat to bond or the gloss of the primer is too large;

3. The paint film is too thick or the paint film layers are not dry, and water vapor is encountered;

4. The baking time is too high or too long (improper construction temperature);

5. Improper paint spraying, coating and other construction operations.

(2) Possible causes of coating falling off

1. There are oil stains or foreign matters on the surface of the substrate, which cannot be completely removed after pre electroplating treatment, resulting in the failure to produce electroplated coating;

2. The substrate has slight and easy to fall off heavy skin. After electroplating, under the action of external force, the coated heavy skin falls off and exposes the substrate;

3. After electroplating, the coating and substrate fall off under the action of large external force (collision, etc.);

4. Since there are many particles on the surface after electroplating, when the particles are removed by external force, the appearance of substrate or primer coating will be exposed;

5. The auxiliary anode is too close to the product surface and the current is too large, resulting in scorching.

Common means

Composition analysis:

See polymer material failure analysis

Thermal analysis:

See polymer material failure analysis

Fracture analysis:

Stereomicroscope (OM)

Scanning electron microscopy (SEM)

Physical properties:

Tensile strength, bending strength, etc

Simulation test (if necessary)

The test shall be carried out under the same working conditions or under simulated working conditions.