SAE J2635 Filiform Corrosion Test Procedure for Painted Aluminum Wheels and Painted Aluminum Wheel Coatings

The “SAE J2635 Filiform Corrosion Test Procedure for Painted Aluminum Wheels and Painted Aluminum Wheel Coatings” standard, developed by the American Society of Automotive Engineers (SAE), describes a laboratory test procedure for evaluating film-like corrosion formation on painted aluminum wheels and wheel coatings. While this test was specifically developed for testing painted aluminum wheels and wheel coatings, it is applicable to other components as well. The application owner should evaluate whether this test produces a film-like corrosion pattern similar to that used in the relevant application to ensure accurate data for the application.

The aim is to establish a uniform testing method for evaluating the corrosion resistance of components for the wheel and rim coating industry. It also aims to reduce the variability of testing procedures, thereby lowering the costs of establishing and maintaining unique testing facilities, test methods, measurement methods, laboratory accreditations, and operator training. The procedure does not establish performance standards for components. Performance standards are determined by test users or customers.

Filiform corrosion occurs when a coated substrate is exposed to a hot and humid environment. This filiform test procedure utilizes the SAE J2634 standard drawing method to ensure continuous exposure of the sample substrate to corrosion products. The test piece is inoculated with corrosion products using the ASTM B368 standard, then immersed in deionized water to remove excess corrosion products, and subsequently placed in a temperature and humidity-controlled test chamber to initiate filiform corrosion formation. After testing, the length of the film thickness, film density, and film thickness area can be evaluated to assess the corrosion resistance of the component.

In the automotive industry, where aesthetics and durability are paramount, the integrity of vehicle components such as wheels is critical. Painted aluminum wheels and coatings are particularly susceptible to a insidious type of corrosion known as filiform corrosion. Filiform corrosion is a thread-like deterioration that can degrade the surface, compromising both appearance and structural integrity. To address this problem, the SAE J2635 standard was developed to simulate and evaluate filiform corrosion in these components. This standard is a vital tool for quality assurance in wheel manufacturing and is applicable not only to aluminum wheels but also to other painted metal surfaces prone to similar corrosion mechanisms.

Often described as worm-like or thread-like, filiform corrosion is a type of atmospheric corrosion that occurs beneath thin organic coatings such as paint or varnish. It typically begins at defects in the coating, such as scratches or cracks, and spreads beneath the film in the form of fine filaments of corrosion products, lifting the film in a characteristic coiled pattern. This type of corrosion is particularly problematic for painted aluminum rims because,

• Aluminum's natural oxide layer provides some protection, but cracks allow chloride ions (from road salt or environmental exposure) to cause anodic dissolution.
• The high surface area of ​​the rims exposes them to changing humidity, temperature fluctuations, and contaminants during vehicle operation.
• Aesthetic damage caused by filigree can lead to customer dissatisfaction, warranty claims, and costly recalls.

Field observations have shown filiformity to be a common type of failure in rims. Therefore, a repeatable laboratory test was needed to predict real-world performance.

The primary objective of the SAE J2635 standard is to establish a uniform and reproducible laboratory method for triggering and measuring filiform corrosion in painted aluminum rims and rim coatings. This test method standardizes the process,

• It allows manufacturers to objectively compare coating systems and pretreatment methods.
• It supports quality control during production.
• It helps with supplier qualifications and compliance with legal regulations.
• It minimizes false positive or negative results by reducing variability in test results between laboratories.

The principles of this method, specifically designed for wheels, can be extended to other coated aluminum components such as body panels or cladding.

The SAE J2635 standard includes a controlled method for simulating environmental stressors. The basic steps of this method are as follows:

• Sample preparation: Representative painted aluminum rims or trim pieces are selected. Controlled defects (scratches), typically 1-2 mm wide, are created using a standard tool to simulate manufacturing defects or wear. Samples are cleaned and dried to remove contaminants.
• Initial exposure (activation phase): Samples are immersed in a 0,1% hydrochloric acid solution for 24 hours or exposed to a chloride-rich environment such as a salt mist chamber. This step activates corrosion zones by allowing chloride ions to penetrate the coating.
• Moisture exposure (spreading phase): Samples are transferred to a controlled humidity chamber at 95-100% relative humidity and 40 degrees Celsius. Exposure is maintained for 1.000 hours or until visible filiform traces form (typically 500-1.000 hours). Direct condensation should be avoided; high humidity promotes filament growth without excessive water accumulation.
• Evaluation and measurement: Samples are collected and filiform features are measured using microscopy or imaging software. Basic measurements include:
• Trace length: The maximum distance between individual filaments (e.g., a maximum of 5 mm is acceptable).
• Scratch frequency: The number of scratches per unit length of scratch.
• Coverage area: Percentage of the affected surface.

Rating scales (e.g., 0-10 severity) or quantitative formulas are used for pass/fail criteria.

In short, the SAE J2635 standard stands out as a cornerstone of corrosion testing in the automotive industry, providing a robust framework for combating filiform corrosion and ensuring painted aluminum wheels meet stringent standards.

For many years, our organization, with its competent and experienced staff, has been understanding the needs of its customers, providing the advanced testing services they require, and assisting in the establishment, implementation, and improvement of management systems. Within this framework, we also provide testing services to businesses in accordance with the "SAE J2635 Filiform corrosion test procedure for painted aluminum wheels and painted aluminum wheel coatings" standard.