PASSIVATING ALUMINUM WITH SurTec 650
Chemical Passivation for Aviation, Defense and Industry
Corrosion Protection
Electrically Conductive
Good Adhesion Base
WE PROTECT THE PROTECTORS
Or at least the materials used in the vehicles. We passivate your aluminum components in accordance with applicable aviation and military standards. Passivation creates a thin, dense conversion coating that provides reliable corrosion protection—while maintaining dimensional accuracy almost entirely. Since the surface’s electrical conductivity is permanently preserved, passivation is particularly suitable for electrical contact surfaces and ground connections. The SurTec coatings act as adhesion promoters for subsequent paint coatings, while the corrosion protection effectively prevents any potential corrosion from spreading underneath.
Because we can.
Since SurTec coatings are virtually invisible, 100% process control is essential. A poorly applied coating usually only becomes apparent as a long-term consequence during use. Trust is good—but perfect workmanship is absolutely essential! We apply the same quality standards as in our anodizing departments!
The Passivation Process:
Passivating Aluminum with SurTec 650
The passivation of aluminum and aluminum alloys with SurTec 650 is a modern chemical conversion process for producing a very thin protective layer that is firmly bonded to the base material. The process replaces chromium VI with trivalent chromium. As a result, SurTec 650 combines high technical performance with today’s environmental and occupational safety requirements. The chemical reaction with the aluminum surface creates a very thin conversion coating. The surface thus retains its dimensional stability to a large extent and maintains its metallic character.
Properties of SurTec 650-passivated aluminum:
Corrosion protection
One of the most important functions of SurTec 650 passivation is the protection of aluminum components against corrosion. The conversion coating reduces direct contact between the aluminum surface and corrosive media, thereby increasing the component’s resistance to environmental influences. SurTec 650 can therefore be used both as a standalone corrosion protection and as a component of a multi-layer corrosion protection system. The thin coating thickness is a significant advantage, particularly for complex, dimensionally stable, or thin-walled components.
Adhesion Promotion Before Painting and Coating
Another important application is the pretreatment of aluminum prior to subsequent painting, powder coating, or other organic coating systems. The chemically generated conversion coating creates a defined surface with significantly enhanced adhesion. This significantly improves the bond with subsequent coatings while simultaneously reducing the risk of corrosion under the paint (filiform corrosion).
Electrically Conductive Surfaces
A particular advantage over many other protective coatings is the ability to use SurTec 650 to produce aluminum surfaces that are both corrosion-protected and permanently electrically conductive. An untreated aluminum surface very quickly forms a natural oxide layer when exposed to air. This layer has comparatively poor electrical conductivity and can lead to fluctuating contact resistances.
Conventional anodic oxide layers are unsuitable for contact points due to their electrical insulation. SurTec 650, on the other hand, provides corrosion protection while maintaining low electrical contact resistance. The manufacturer specifies a contact resistance of < 5,000 µΩ per square inch for this process.
Significance for Aviation and Military Technology
Chemical conversion coatings on aluminum have been of great importance in aircraft construction and military applications for decades. These applications place high demands on corrosion resistance, paint adhesion, process reliability, and—for certain components—electrical contact performance. A key military specification is MIL-DTL-5541—“Chemical Conversion Coatings on Aluminum and Aluminum Alloys.” The specification remains active; the current validation of Revision F took place in 2024. Among other things, MIL-DTL-5541 distinguishes between:
Type I: Processes using hexavalent chromium (Cr(VI))
Type II: Processes without hexavalent chromium
SurTec 650 belongs to Type II due to its Cr(VI)-free chemistry.
In addition, the standard distinguishes between two important performance classes:
Class 1A – maximum corrosion protection
This class is intended for high corrosion protection and can be used both for unpainted surfaces and as a pretreatment for aluminum components that will subsequently be painted.
Class 3 – Corrosion protection with low electrical resistance
This class is intended specifically for electrical and electronic applications where, in addition to corrosion protection, the lowest possible electrical contact resistance is required.
SurTec 650 is approved in accordance with MIL-DTL-81706B for Class 1A and Class 3. This makes the process particularly suitable for applications where the requirements of MIL-DTL-5541 for corresponding chemical conversion coatings are mandated. Another important specification from the aerospace sector is SAE AMS 2473 – “Chemical Film Treatment for Aluminum Alloys – General Purpose Coating.” The standard describes requirements for chemical conversion coatings on aluminum alloys. The current edition is AMS 2473K, published in May 2025.
Details on Passivation
- Corrosion Protection
- Electrically Conductive
- Good Adhesion Base
Conversion coatings can be formed on virtually all common wrought aluminum alloys.
Unlike anodizing, passivation does not result in any measurable coating growth beyond the base surface (see sketch above). Since the passivation layer is only a fraction of a micrometer thick, the as-machined dimension remains virtually unchanged after treatment—unlike with anodizing, no additional allowance is required in the design.
Typical coating thicknesses for SurTec 650 range from 80 to 100 nm, i.e., <1 µm.
Unlike anodizing, where layer hardness is the key parameter, the electrical contact resistance is the decisive parameter in passivation, since the layer—unlike the insulating anodized layer—is intended to remain conductive. Depending on the process and standard (e.g., MIL-DTL-81706B), values well below 35 mOhm·cm² are achieved.
Free initial consultation
Then get in touch with us and benefit from a consultation at eye level, without waiting in line. You will receive individual advice and a dedicated contact person. Thanks to our many years of experience, we are also happy to support you in the planning phase. Because we always have a plan.
Our Processes
Blasting technology
Apple really got it started – now everyone wants a piece of it...
Laser marking
The guaranteed upgrade to first class for your premium product