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Selective coatings

Selective coatings

Selective finishing of metal surfaces

The area of selective coating covers all processes during which, for technical or functional reasons, workpieces are only partially coated. While this allows for the targeted protection of component areas which are subject to heavy loads, the remaining surface remains available for other treatments (e.g. grounding).

How the area to be coated is isolated, whether by targeted coating applications or by masking certain areas of the component, is ultimately determined by the process. With LASOX-COAT® and SELGA-COAT®, Aalberts surface treatment currently offers two selective coating methods.

SELGA-COAT<sup>®</sup> process

SELGA-COAT® is a selective plating process for metal surfaces. Areas that do not require plating are covered inside a tool with a built-in sealing system. After that, an electrolyte is pumped into the tool housing. It flows around the area to be coated to galvanize it. When aluminum alloys are finished with hard anodizing processes, the workpiece is used as the anode.

SELGA-COAT® coatings on aluminum materials are partial anodic coatings. Compared to conventionally applied coatings, they come with markedly improved characteristics, such as:

  • excellent covering capacity
  • increased corrosion resistance
  • improved coating hardness
  • faster build-up of layers
  • uniform structures
  • improved leveling capabilities
  • low degree of roughening
  • enhanced purity

Once a surface has been partially coated with SELGA-COAT®, mechanical rework can be omitted in most cases.

Depending on the application, the layers can be produced via Cr6-containing* or Cr6-free electrolytes.

*Request for authorization submitted via Hapoc GmbH & Co. KG.

Selective coating

When used as industrial coating, SELGA-COAT® is primarily applied in the automotive and mechanical engineering sectors. On the one hand, this is due to the fact that components are produced in large quantities, and on the other hand, the requirements placed on the coatings are extremely demanding. This selective hard anodizing process has proven highly effective for vehicle components. Within the scope of large-scale orders, Aalberts surface treatment has successfully coated braking systems, gearbox components, (diesel and gasoline) motor pistons, pump housings (servo-steering), wheel hubs and bearings, valves (e.g. injection pumps), valve pistons (automatic transmission) and spacer plates (automatic transmission).

When it comes to the partial deposition of metal, we use the component surface as the cathode in the circuit opposite to the tool housing. The actual hard chrome deposition (SELGA-COAT® CHROME) occurs in an enclosed system - without open chromic acid solution containers. The system works without waste water, whereas the used chemicals are almost fully returned to the cycle. SELGA-COAT® CHROME is a selective, eco-friendly process exempt from REACH, the EU Chemicals Regulation, according to which the use of hexavalent chromium has been banned in most cases since September 2017.

Compared to common hard anodizing processes, the current density of SELGA-COAT® CHROME is far higher, which results in the following favorable characteristics: extremely fast deposition, high degrees of hardness, increased corrosion resistance, low degrees of roughness and very narrow coating tolerances.

Elongated components, such as axes, spindles, shafts or pipes, are ideal for hard anodizing using SELGA-COAT® CHROME.

When it comes to the selective deposition of gold, the component surface is used as the cathode. The SELGA-COAT® GOLD layers created in this way are characterized by high ductility, resistance to tarnishing and good solderability. Their low, specific electrical resistance offers further advantages.

SELGA-COAT® GOLD coatings are very much sought after when it comes to contact components. Using our process, the contact areas in your electrical devices can be reliably connected by a gold layer. Our targeted partial coatings minimize the consumption of gold, and thus your costs.


Base Materials


  • Wrought aluminum alloys
  • Cast aluminum alloys


  • Aluminum die casting alloys
  • Unalloyed steel


  • Hardened steel
  • Almost all metals and metal alloys

LASOX-COAT® is a selective coating process involving the laser-induced formation of aluminum oxide. When exposed to laser radiation, the alloy particles on the surface of the component to be processed melt and vaporize. Oxygen plasma and part of the molten aluminum react to form aluminum oxide (corundum, Al2O3), which now covers the treated surface. Underneath the corundum layer there is a remelt zone whose thickness is approximately 10 times greater.

Since the laser beam is guided across the workpiece surface section by section, the coating duration is proportionate to the area to be coated. Using this selective coating process, we can also create letterings, individual lines or complex shapes and patterns.

The great advantage of selective coating methods, as opposed to electroplating processes, is the fact that they do not require any process chemicals, such as acid electrolytes. That is why it is not difficult at all to have LASOX-COAT® plants authorized. LASOX-COAT® plants are enclosed and rated as Class 4 lasers according to EN 60825-1. Therefore, they can be easily incorporated into existing production lines.

The LASOX-COAT® process increases the wear resistance of component surfaces to a significant extent. It produces extremely hard and durable aluminum oxide, because it does not create any micro-pores in the oxide layer.

In order to increase a component's resistance to wear, it is not always necessary to coat its entire surface. Even surfaces coated in a “tartan pattern” are already more resistant to wear.

In general, almost all aluminum alloys may be coated with LASOX-COAT®. In individual cases, however, it is advisable to first clarify the desired surface characteristics in order to determine the type of alloy suitable for the LASOX-COAT® process.

The LASOX-COAT® process is preferably used for the selective coating of those areas of a workpiece surface which are continuously subjected to wear, such as a housing rim repeatedly hit by a cover that is opened and closed or the impeller of a pump which is subject to partial wear. Further common applications include laser markings and labeling on aluminum components for traceability and documentation purposes. The process is also used for the surface treatment of pneumatic valves, proportional valves, brake pistons, hydraulic shutters and pneumatic shutters.

  • Why are selective coating processes eco-friendly?

    Performed in a closed circulation system, the SELGA-COAT® process introduces fewer contaminants into the coating process than classic immersion processes. Selective coating processes minimize the loss and ultimately the consumption of electrolytes. This protects the environment.

    LASOX-COAT® is a selective coating process involving the laser-induced formation of aluminum oxide. This process is eco-friendly because it is done without the use of process chemicals (such as acid electrolytes).

  • What does the name SELGA-COAT® stand for?

    SELGA stands for SELective GAlvanizing. The SELGA-COAT® process is ideal for the selective galvanization of geometrically sophisticated components produced in high volumes.

  • What is so special about the SELGA-COAT® process?

    During the SELGA-COAT® process, only the functional surface of the component is passed and coated by the electrolyte using electric current. The components do not have to be masked nor do they require any mechanical rework.

  • Is it possible for customers to perform partial coating processes at their premises?

    Yes, Aalberts surface treatment specializes in designing LASOX-COAT® and SELGA-COAT® plants for incorporation into existing production lines.

Product enquiry

If you would like to tell us something about the product presented here, you are welcome to do so. Your enquiry, your comment, your wishes will be forwarded directly to your personal contact person.

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  • Powder coating

    Powder coating

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