Alodine / Chromate Conversion

Gold Hexavalent Chromate Conversion Coating

At Electromold we perform an immersion process creating a Chemical Conversion coating on aluminium. These coatings are designed to provide improved corrosion resistance and a superior surface for better adhesion of primers and paints on bare aluminium. The treatment converts the aluminium surface with a superficial layer containing a mixture of chromium compounds, producing an aluminium oxide and chromic oxide layer.  At Electromold we call this coating Alodine or as it more commonly known "Chromate Conversion".

Currently there are two types of Chemical Conversion coatings available and Electromold is able to perform both types. One is the normal Hexavalent chromium type that is goldish in colour and the other is the New RoHS approved Trivalent chromium type that has a slight faint bluey tinge and on some aluminium a pale tan visible appearance. (RoHS stands for “Restriction of Hazardous Substances”).

All chromate conversion coatings use chromic acid in the form of its soluble salts. During the process, a thin film is produced on the aluminium surface. 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.

The oxide files produced by this process vary in colour from iridescent golden tan, depending on the aluminium alloy being treated, surface conditions, and the class of chromate requested.

There are generally two types classes available, Class 3 coatings are a lighter film and provide an excellent preparation for paint applications while still providing great electrical conductivity. Class 1A coatings are a heavier coating and are used for increased corrosion protection.

Both Class 1A and 3 coatings performed by Electromold conform to the following Military Specifications and pass a 5% neutral salt spray test at 168 Hours. The two most common specifications are MIL-C-5541 Class 1A or 3 and MIL-DTL-5541, Type 1 Class 1A or 3 (Note: These types of conversion coatings ARE NOT RoHS compliant. “Restriction of Hazardous Substances”).

Names that are commonly used on drawings to request this process include Iradite, Alodine, Chromate Conversion coat and Alocrom.

Properties

  • Increased Corrosion Resistance (no sign of corrosion after 168 hours at 5% neutral salt spray test IAW ASTM B117)
  • Class 1A coatings are intended for use to provide corrosion protection
  • Improves paint adhesion for a range of finishes
  • 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
  • Hexavalent chromium used
  • Works on alloyed and cast aluminium
  • Inexpensive

Clear Trivalent Chromate Conversion Coating RoHS compliant. (SurTec 650 CHROMITAL TCP)

Electromold has researched over a period of time and implemented this new RoHS Clear Trivalent Conversion Coating process which meets all specification requirements and complies with all import / export environment regulations. We are proud to offer this environmentally friendly process and show that we are keeping with global trends to help provide better and safer alternatives.

With this global trend many Australian and international manufacturers are designing componentry with this RoHS Conversion coating as a standard, and Electromold now has the ability to support these manufacturers. Electromold is one of the first process facilities in Australia to implement this product and service and continues to be a leader in the field of implementing the latest technologies in surface coatings.

Here is some information on our new Clear Chromate Conversion Coating solution for aluminium which is RoHS approved.

Properties

  • Hexavalent chromium free passivation for aluminium
  • Based on trivalent chromium
  • Excellent bare corrosion protection comparable to hexavalent passivation
  • Also works on alloyed and cast aluminium
  • Improves paint adhesion for a range of finishes
  • Suitable as pretreatment before lacquering, powder coating and gluing
  • Produces an iridescent, faintly blue to tan visible layer
  • SurTec 650 meets and exceeds MIL-DTL-81706 and MIL-DTL-5541 Type 2 for bare corrosion (336hrs in NNS per ASTM B-117, respectively, DIN 50021 SS) and now in some cases out performs normal Chromate Coating
  • Low contact resistance, <0.8 mOhm/cm sq
  • Heat resistance up to 100 deg C with minimal loss in corrosion resistance
  • Inexpensive

If you require any further information regarding this process or any of Electromold’s plating processes, please contact us on (03) 9464 0922 and one of our technical staff will be able to assist you.