SurTec 650

SurTec 650 is a chemical conversion treatment for aluminium alloys. The process consists in immersing the metal in a solution containing chromium III salts and an oxidizing agent (nitrate ions...). The consumption of protons and the reduction of nitrates induce a local increase in pH, leading to the precipitation of trivalent chromium hydroxide on the surface.

Description off the process

The purpose of this chemical conversion is to give the treated part protection against corrosion and to ensure electrical continuity between the surfaces in contact.

  • Appearance : depending on the alloy, colourless to iridescent blue-green tint
  • Layer weight : 2 to 5 mg/dm².
  • Surface condition : micro-cracked layer / little impact on roughness
  • Electric conductivity : < 32,25 mOhm per 1cm² (< 5000 μOhm per square inch)

Relevant substrates

Mainly 5000 and 6000 series alloys and castings. For the other alloys (2000 and 7000 series), the level of performance obtained varies greatly from one alloy to another and from one production method to another.


• Corrosion resistance in a slightly aggressive environment
• Base for adhesion of organic coatings (paints, glues...)
• Can be applied by swab or spray
• Suitable as a pre-treatment before painting, powder coating and gluing, but also as a post-treatment after anodizing.
• Can also be used as a conversion on magnesium

Sectors concerned: Aeronautics, automotive, building, street furniture…

Selection criteria - limitations

• The corrosion resistance of hexavalent chromium-free conversion layers is often lower than that of chromium VI-based chromate layers.
• The application of a paint system is desirable, as in the case of chromating, when optimum corrosion protection is required.
• The performance level on the 2000 and 7000 series is still limited.

Environnemental impact

This process is not impacted by ELV, RoHS or REACH regulations.


  • LN 9368-3 number ID 1108
  • DIN 50935-2, type A
  • MIL-DTL-81706 and MIL-DTL-5541F
  • ISO 8081 : Method of measurement of mass per unit area
  • ISO 9227-NSS : Neutral salt spray test
  • EN 12 373-18 : pitting corrosion rating system