Protecting Automotive Metal Parts with Additives

Photo: carlos aranda / Unsplash

The production of automotive components places high demands on material resistance to corrosion, wear, and extreme temperatures. Additives such as corrosion inhibitors, friction modifiers, or antioxidant agents play a crucial role in extending the lifespan of components, whether for car bodies, engine parts, or chassis systems. However, the correct application of these substances requires adherence to technological procedures to achieve optimal results without compromising quality or safety. This article provides you with specific steps for selecting and applying additives in the automotive industry.

1. Selecting the Right Type of Additive Based on Material and Operating Conditions

Before the actual application, it is crucial to select additives that correspond to the specific metal material and the conditions to which the part will be exposed. In the automotive industry, we most commonly encounter steel, aluminium, magnesium, or alloys, with each material requiring a different approach. For example, phosphate- or amine-based additives are suitable for steel parts exposed to high humidity or salt solutions, whereas corrosion inhibitors based on silanes or organic acids are more frequently used for aluminium components. It is also important to consider operating temperatures – some additives lose their effectiveness at temperatures above 150 °C, while others are designed for extreme conditions up to 300 °C.

Another factor is compatibility with other materials in the system, such as lubricants, seals, or coatings. Additives must not react with these materials to prevent their degradation or loss of functionality. Before selection, it is advisable to consult the manufacturers' technical data sheets and conduct laboratory compatibility tests. In case of uncertainty, universal additives with a broad spectrum of effectiveness, designed for combined materials and various operating conditions, can be used. However, it always holds true that specialised additives for a specific application provide better protection than universal solutions.

2. Preparation of metal part surfaces before additive application

The quality of the metal part's surface has a fundamental impact on the effectiveness of the applied additive. Before the actual application, it is necessary to remove all impurities such as oils, greases, dust, rust, or residues of previous coatings. The standard procedure includes degreasing using alkaline or solvent-based cleaning agents, followed by rinsing with demineralised water. To remove rust and oxides, mechanical grinding, sandblasting, or chemical pickling, for example with phosphoric or citric acid, is used. It is important that the surface is dry and free of cleaning agent residues after cleaning, which could contaminate the additive.

After cleaning, it is advisable to inspect the surface, for example, using a wettability test (water break test) or visual inspection under UV light if fluorescent cleaning agents were used. The surface should be homogeneous and free of visible defects. In some cases, especially for critical components, it is recommended to apply a conversion coating (such as phosphating or chromating) to improve additive adhesion and enhance corrosion protection. However, this layer must be compatible with the selected additive to avoid undesirable chemical reactions.

Photo: engin akyurt / Unsplash

3. Proper additive application: methods and technological processes

The application of the additive can be carried out in several ways, depending on the type of part, the required layer thickness, and production conditions. The most common methods include dipping, spraying, brush or roller application, and electrophoretic deposition. For serial production in the automotive industry, dipping or spraying is often used, as these methods allow for even coverage of complex geometries. When dipping, it is important to control the bath temperature (usually between 20–60 °C) and immersion time (from a few seconds to several minutes) to achieve the optimal layer thickness without excess or deficiency.

When spraying, the correct pressure setting (usually 2–5 bar) and nozzle distance from the surface (15–30 cm) are crucial to prevent droplet formation or uneven coverage. For some additives, specific drying conditions must be observed, such as forced air circulation or elevated temperature (up to 120 °C). It is always necessary to follow the additive manufacturer’s recommendations, especially regarding drying time between individual layers. In multi-layer systems, it is important to maintain intervals between applications to avoid damaging the previous layer.

4. Quality Control and Maintenance of the Protective Layer After Application

After applying the additive, quality control is essential to verify the effectiveness of the protection and compliance with technical parameters. Visual inspection includes assessing layer uniformity, the absence of bubbles, cracks, or exposed areas. For more precise evaluation, non-destructive methods are used, such as measuring layer thickness using magnetic or eddy current methods, or adhesion tests (e.g., cross-cut test according to applicable standards). For critical components, corrosion tests, such as salt spray or cyclic humidity and temperature tests, are recommended to simulate real operating conditions.

Maintaining the protective layer is just as important as the application itself. During the service life of the part, it is necessary to regularly check the condition of the additive, especially in areas exposed to mechanical wear or chemical influences. If damage occurs, the layer must be repaired or reapplied to prevent local corrosion. For some additives, periodic treatment is possible, for example, using sprays or pastes that restore protective properties. It is also important to monitor changes in operating conditions that may require adjustments to the type or frequency of maintenance.

Photo: Elena Mozhvilo / Unsplash

Optimizing additive dosage for maximum efficiency and cost-effectiveness

The dosage of the additive is a key factor that influences both the protective effect and processing costs. An excessively low concentration will not provide sufficient protection against corrosion, abrasion, or chemical degradation, while an excessive amount can lead to undesirable side effects, such as the formation of a greasy film, reduced adhesion of subsequent layers, or increased costs. In general, it is recommended to follow the manufacturer's technical documentation, which specifies the recommended concentrations for specific applications – for example, 0.5 to 2 % by weight for corrosion inhibitors in coolants or 1 to 5 % for preservative oils.

In practice, however, it is often necessary to adjust the dosage to the specific production conditions. For instance, for parts exposed to high mechanical stress or extreme temperatures, it may be advisable to increase the concentration by 20–30 % above the standard recommendation. Conversely, for static components or parts stored in a controlled environment, the dosage can be reduced. To precisely determine the optimal amount, it is advisable to conduct a series of tests with varying concentrations and evaluate the results using standard test methods, such as the salt spray test or abrasion resistance test.

Compatibility of additives with other materials and processes in the production chain

Metal protection additives often come into contact with other materials, such as lubricants, coatings, adhesives, or sealants. Their mutual compatibility is crucial for ensuring the long-term functionality and stability of the entire system. For example, some corrosion inhibitors may negatively affect the adhesion of subsequent coating layers, while others may react with elastomers in seals, causing their degradation. Therefore, before introducing a new additive into production, it is essential to perform compatibility tests with all relevant materials.

Testing should include both short-term tests (e.g., coating adhesion test after additive application) and long-term exposure in simulated operating conditions. It is also important to consider the temperature and mechanical stress to which the parts will be subjected. In the automotive industry, combined tests are often used, where samples are exposed to cyclic changes in temperature, humidity, and mechanical loading. The results of these tests help identify potential issues and allow for the optimization of additive selection to ensure compatibility with all materials and processes in the production chain.

Environmental and Safety Aspects of Working with Metal Protection Additives

Working with chemical additives requires compliance with strict safety and environmental regulations, particularly in relation to REACH and CLP/GHS regulations. Before handling additives, it is necessary to familiarize yourself with the Safety Data Sheet (SDS), which contains information on the hazardous properties of the substance, protective measures, and procedures in case of an accident. For example, some additives may be classified as irritants, toxic, or hazardous to the environment, which requires the use of personal protective equipment (PPE) and special procedures for handling and storage.

The environmental aspect is equally important, especially when disposing of waste substances or rinse water. Many additives contain substances that can contaminate water sources or soil, so they must be processed in accordance with applicable regulations. In practice, this means using closed systems for additive application, recycling rinse water, or treating it before discharge into the sewer system. Adhering to these measures not only minimizes environmental risks but also protects workers' health and ensures compliance with legislative requirements.

Need a consultation on additive selection?

Every application requires an individual approach – whether it's coating systems, lubricants, or corrosion inhibitors. GCG Group provides complete technical support for supplied raw materials, including safety data sheets and application recommendations, so you can achieve maximum efficiency and reliability. Contact us – or browse our catalog of over 1,300 products.