Chemical Conversion Coatings

Electromold Australia performs two chemical conversion coating processes on aluminium and aluminium alloys, the immersion method provides maximum corrosion resistance and a superior surface for improved adhesion of primers, paints, lacquers, glue etc on bare aluminium substrates. The treatment converts the aluminium surface with a superficial layer containing a mixture of chromium and non-chromium compounds, the following specifies the different coating available at Electromold meeting the industry specification MIL-DTL-81706 and/or more commonly known as MIL-DTL-5541.

Chromium Conversion Coating – MIL-DTL-5541 Type I, Class 1A & Class 3

Alodine® 1200s produces a protective coating on aluminium and aluminium alloys which ranges in color from light iridescent golden to tan. The process is operated at room temperature, chromate is an excellent treatment method for paint or adhesives since it greatly enhances the products ability to form a bond with the aluminium. It is frequently used on electrical and electronic equipment, the benefits are coating that provides increased corrosion resistance while remaining electrically conductive when controlling the coating weight.

There are generally two classes available, Class 3 coatings are a lighter film and provide an excellent preparation for paint applications with low electrical resistance properties. Class 1A coatings are a heavier coating and are used for increased corrosion protection.

Chromium Free Conversion Coating – MIL-DTL-5541 Type II, Class 1A & Class 3

SurTec 650 (chromitAL®) is a chromium(VI)-free trivalent passivation for aluminium. The liquid concentrate delivers an excellent corrosion protection, comparable with the corrosion protection of a hexavalent passivation or Type I coatings.

SurTec 650 is suitable for alloyed and casted aluminium and pre-treatment before priming, laquering, powder coating and gluing. Application method is by immersion producing an iridescent, faintly blue to tan colour layer.

It can be used on electrical and electronic equipment, the benefits are coating that provides increased corrosion resistance while remaining electrically conductive.

As per the Type I, there are two classes available, Class 3 coatings are a lighter film and provide an excellent preparation for paint applications with low electrical resistance properties. Class 1A coatings are a heavier coating and are used for increased corrosion protection.

Compliance

The two chemical conversion coating materials (Type I and Type II) are listed on the latest electronic version of the Qualified Products List, QPL-81706.

Both processes have been qualified per MIL-DTL-81706, periodic testing is carried out per the requirements of MIL-DTL-5541F for Class 1A and Class 3 consisting of a 5% neutral salt spray test at 168 hours, paint adhesion, low electrical resistance (checked 6 monthly) and coating weight validation maintaining a repeatable process. 

Properties

  • Increased corrosion resistance when tested for 168 hours at a 5% neutral salt spray, testing carried out per industry specification ASTM B117
  • Class 1A coatings are intended for use to provide maximum corrosion protection
  • Class 3 coatings are intended for use where lower electrical contact resistance is required, as tested passes 168 hours 5% neutral salt spray test IAW ASTM B117
  • Improves paint adhesion for a range of finishes
  • Type I - Hexavalent chromium used
  • Type II – Non-hexavalent trivalent passivation used
  • Works on most aluminium alloys including cast aluminium

(For cast aluminium, suggest speaking with an Electromold technical representative)

  • Inexpensive coating for aluminium alloys when needing increased corrosion protection or adhesion properties
If you require any further information regarding this process or any of Electromold's plating processes, please contact us on +61 3 9464 0922 and one of our technical staff will be able to assist you.