ForMatter/Finishes/coating/Chromate conversion (Alodine / Iridite)
finish_coating_chromate_alodine

Chromate conversion (Alodine / Iridite)

coating · patinated · Alodine, Iridite, chem film, chromate film, MIL-DTL-5541

A thin, electrically conductive, gold-iridescent layer formed when aluminum reacts with a chromate solution. Used as paint-prep, as a corrosion barrier on its own, or as a conductive ground point on aluminum chassis (the bare-aluminum-under-the-EMI-gasket finish). Standard on aerospace hardware. Reads as a soft gold-tint over aluminum.

Chromate conversion coating per MIL-DTL-5541. Aluminum dipped in hexavalent chromate solution (Alodine 1200) or trivalent (RoHS-compliant Alodine 5700, SurTec 650): chromate reacts with the surface to form a 0.5–4 µm chromium-aluminum-oxide layer. Color soft gold to brown depending on dwell time and chemistry. Electrically conductive (sheet resistance < 5 mΩ); paint-key for primer adhesion; corrosion barrier. Hexavalent chromate is being phased out under REACH / RoHS; trivalent is the modern spec but reads slightly less gold. Distinct from anodizing — chromate is a chemical conversion, no electricity, no separate substrate-thickness change beyond the film itself.

character — soft gold-iridescent over aluminum, conductive, paint-prep register.

Finish properties

  • levelpatinated
  • subcategorychromate conversion coating
  • applies tometal

Incompatibilities

  • REACH / RoHS-restricted regions for hexavalent formulations
  • stainless / carbon steel — wrong substrate chemistry

Second life

reversibilitymoderate — most coatings can be stripped chemically (methylene chloride for paint, NaOH for some powder coats) or thermally / mechanically (sandblasting). Some specialty coatings (DLC, ceramic) require commercial-service strip.
blocks substrate recyclingno
renewabilityfield- to shop-renewable — most paint and clear coats can be touched up or re-coated in service; powder coat and PVD coatings require a coating-house re-application.

SSPC / NACE surface-coating standards; manufacturer technical literature for the specific coating chemistry.

Citations