GMW 15287 Fine Thread Corrosion Test for Painted Aluminum Wheels

Developed by General Motors Worldwide (GMW), the “GMW 15287 Fine Thread Corrosion Test for Painted Aluminum Wheels” is a test standard used to evaluate the resistance of painted aluminum wheels and painted aluminum wheel coatings to fine thread corrosion.

Thread corrosion is a specific type of corrosion that develops beneath an organic coating, typically paint. It appears as fine, thread-like corrosion marks that can grow outwards from scratches, exposed edges, or coating defects. Because aluminum rims are exposed to moisture, salts, temperature variations, and road contaminants, controlling this type of corrosion is important for both appearance and long-term coating performance.

Thread corrosion is a subfilm corrosion mechanism. When the protective coating is locally damaged or punctured, moisture and corrosive substances can reach the aluminum substrate. Corrosion can then spread along narrow, thread-like paths beneath the coating. Unlike general surface corrosion, thread-like corrosion can be difficult to detect initially. However, it can gradually lead to:

• Thread-like corrosion patterns under the paint.
• Loss of coating adhesion
• Blistering or peeling of the coating
• Spread of corrosion from damaged areas.
• Deterioration of the rim appearance.
• Gradual deterioration of the protective coating

For painted aluminum rims, these effects can become particularly significant, as the rims are constantly exposed to a harsh outdoor environment.

The primary purpose of the GMW 15287 standard is to provide a controlled laboratory procedure to determine whether a painted aluminum wheel or wheel trim has adequate resistance to thread-like corrosion. This test helps manufacturers and suppliers evaluate the following aspects:

• Durability of the paint system
• Corrosion protection for aluminum.
• Coating performance after local damage.
• Resistance to corrosion propagation under the coating.
• Suitability of a coating system for automotive wheel applications.

The GMW 15287 standard is more specifically related to painted aluminum wheels and painted aluminum wheel covers, rather than being a general corrosion test for every automotive component.

In principle, this test method is based on exposing properly prepared and damaged coated aluminum samples to an aggressive corrosive environment, followed by the creation of conditions favorable for the development of filamentous corrosion.

In general, this method follows these steps:

• Sample preparation: Samples of painted aluminum rims or wheel covers are prepared according to standards. Coating status, sample dimensions, and preparation procedure are important because they can significantly affect corrosion propagation.
• Creating a coating defect: A controlled defect or scratch can be created to expose the aluminum beneath the coating. This provides a starting point for corrosion.
• Accelerated corrosion exposure: Samples are exposed to a CASS environment. This aggressive environment accelerates corrosion processes that can begin and spread beneath the coating. Therefore, this standard differs from ordinary moisture or neutral salt spray tests.
• Moisture exposure: After the initial corrosion exposure, samples are placed in a controlled high-humidity environment. This creates favorable conditions for the development of filamentous corrosion beneath the coating.
• Periodic evaluation: Samples are examined during or after exposure. The evaluator looks for signs of filamentous corrosion and assesses the extent of corrosion spread from the site of onset.

It's not just the presence of corrosion that matters, but also the extent and appearance of corrosion penetration beneath the coating. Typical observations might include:

• Number and density of corrosion filaments
• Length of corrosion marks
• Direction and pattern of spread

• Corrosion spreading from an artificial defect.
• Blistering or peeling of the coating
• General deterioration of the coating.

The applicable General Motors specification or engineering drawing determines the acceptance criteria. Therefore, passing the GMW 15287 standard does not mean that every application uses the same numerical acceptance limit.

GMW 15287 standard is considered important for the following reasons:

• It preserves the rim's appearance: Aluminum rims are highly visible components on vehicles. Thread-like corrosion can create noticeable thread-like marks under the paint, significantly reducing visual quality.
• It evaluates the quality of the coating system: The test provides information about the interaction between the aluminum substrate, pretreatment, primer, paint layers, and finishing system.
• It helps prevent premature coating failure: A coating may appear acceptable under normal conditions, but be susceptible to corrosion spread after a minor defect. This standard provides an accelerated way to investigate this susceptibility.
• Supports supplier and process competence: Automotive wheel manufacturers and coating suppliers can use this test during material and process development to compare different coating systems and verify performance requirements.
• It provides automotive-specific corrosion assessment: This standard is specifically defined for painted aluminum wheels and painted aluminum wheel covers. Therefore, it addresses an application where both coating appearance and corrosion resistance are important.

GMW 15287 standard is closely related to SAE J2635 standard, which defines a filiform corrosion test procedure for painted aluminum wheels and wheel covers. Accredited laboratories often list both methods together for filiform corrosion testing. However, laboratories should not assume that the two standards are automatically interchangeable for a particular customer program. The required method, revision, sample preparation, exposure conditions, and acceptance criteria must be validated against the relevant engineering requirement.

GMW 15287 standard is primarily related to the following standards:

• GMW 15287 Fibrous corrosion of painted aluminum wheels and wheel covers
• GMW 14872 Cyclic corrosion laboratory test
• GMW 14458 CASS corrosion test
• GMW 14729 High humidity test
• ASTM B117 General salt spray/mist exposure
• SAE J2635 Filamentous corrosion of painted aluminum rims

Therefore, the GMW 15287 standard should not be considered merely a salt spray test. Its purpose is to evaluate filamentous corrosion beneath the coating using an accelerated circumferential array designed specifically for painted aluminum wheel applications.

GMW 15287 standard may relate to the following:

• Painted aluminum wheels
• Painted aluminum wheel covers
• Automotive wheel retreading systems
• Aluminum surfaces with organic protective coatings.
• Wheel retreading development and verification.
• Supplier qualification
• Production process verification

Consequently, the GMW 15287 standard uses accelerated environmental exposure to induce corrosion beneath the coating, allowing engineers to assess how effectively a coating system resists such degradation.

This standard is particularly valuable because aluminum rims must combine corrosion protection, coating durability, and high cosmetic quality. A coating that performs well in a standard salt spray test may not provide adequate protection against filamentous corrosion. Therefore, this standard allows for a more targeted assessment of this specific failure mechanism.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its clients, providing the advanced testing services they require, and assisting them in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services in accordance with the GMW 15287 standard.