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Chromate Conversion Coating Services

Clear Chromatizing is an alternative to Yellow Chromatization which is chrome free, it provides a clear iridescent film of low contact resistance. The corrosion performance of our aluminium chromate conversion coating is consistent with that of traditional hexavalent processes and is largely a function of the specific alloy that the aluminium chromate conversion coating is applied to. Aluminium chromate conversion coating improve the corrosion resistance of wrought, heat treatable and cast aluminium alloys while providing an excellent base for subsequent painting or power coating services. We provide as per Mil & ASTM standards.

 

In the process a thin oxide layer is formed to provide corrosion resistance to the bare aluminium. Instead of using bare Aluminium this process is recommended to prevent oxidisation. It can also be used instead of primer to provide strong adhesion for further coating like powder coating or paints. The coating thickness is very thin usually counted in nano microns. At our place we can provide the dye testing to feel the difference bare aluminium and clear chromatized component.

 

Hexavalent Chromate Conversion Coating is a type of conversion coating used to passivate aluminium. It provides high corrosion resistance and paint adhesion properties to aluminium surface, it is well known that the visual desirability may be improved by forming a chromate coating by contacting the surface with an aqueous conversion coating solution containing chromium ions and other additives.

 

Aluminium Bright Finishing is chemically treated to give extra brightness to the aluminium components. Usually Anodizing is a dull/matt finish, and in order to give the shiny finish we do the additional chemical treatment.

 

Non Hexavalent Chromatization specification covers the requirements relating to rinsed and non-rinsed non-hexavalent chromium conversion coatings on aluminium and aluminium alloys intended to retard corrosion; as a base for organic films including paints, plastics, and adhesives; and as.a protective coating having a low electrical contact impedance. Coatings are categorized into four classes according to corrosion protection and finish. The type of conversion coating depends on the composition of the solution and may also be affected by pH, temperature, duration of the treatment, and the nature and surface condition. Films are normally applied by dipping. Coatings shall adhere to specified electrical resistance, adhesion, and corrosion resistance requirements.

 

Chromatization, Aluminium and aluminium alloys are treated by a corrosion resistant conversion coating that is called "chromate coating" or "chromating". General method is to clean the aluminium surface and then apply an acidic chromium composition on that clean surface. Chromium conversion coatings are highly corrosion resistant and provide excellent retention of subsequent coatings. Different type of subsequent coatings can be applied to the chromate conversion coating to produce an acceptable surface.

 

Along with providing high corrosion resistance and paint adhesion properties to aluminium surface, it is well known that the visual desirability may be improved by forming a chromate coating by contacting the surface with an aqueous conversion coating solution containing chromium ions and other additives.

 

Quality of surface pre-treatment prior to powder coating is the most important factor that effects to stability of paintings. Properly pre-treated aluminium surfaces become highly protected against corrosion even if the surface is exposed to external impacts ( damage, high temperature, humidity…etc. ). Chromating is generally used as under paint protection. Coating weight on the surface varies between 0.2 -2.0 gr/m² when coating solution is applied to surface by immersion or spraying. Coating weight is variable according to concentration, application time, temperature and pH of the coating solution. Out of proper operation parameters coating weight quality of the  coating will reduce. Thicker coating does not mean high quality coating.
 

Most commonly, chromating is provided by yellow chromating (Cr+6), green chromating (Cr+3), transparent chromating  (Cr+3).
 

Coating quality will be effected positively when surface treated with deionized water after chromating. Refinishing of the rinsing baths also improve the quality of the coating. Chromated and rinsed aluminium workpieces should be dried in driers or ovens but it is important not to set drying temperatures above 70°C. After all these treatment workpieces are painted then cured 10 – 15 minutes at 200°C for subsequent application of powder coating.

 

Process line of chromate conversion coating can be set up as follows;

 

Simple Process;

  1. Acidic Degreasing,
  2. Water Rinsing,
  3. Water Rinsing,
  4. Chromating,
  5. Water Rinsing,
  6. Drying.

 

Advanced Process;

  1. Degreasing,
  2. Water Rinsing,
  3. Caustic Treatment,
  4. Water Rinsing,
  5. Nitric Acid Treatment,
  6. Water Rinsing,
  7. Chromating,
  8. Water Rinsing,
  9. Drying.

 

Aluminum Chromate Conversion Coating per MIL-C-5541 (MIL-DTL-5541) and ASTM B449-93.

The chromate process provides a clear iridescent to  slightly golden iridescent film of low contact resistance. The corrosion performance of our aluminium chromate conversion coating is consistent with that of traditional hexavalent processes and is largely a function of the specific alloy that the aluminum chromate conversion coating is applied to.

Aluminum chromate conversion coating improve the corrosion resistance of wrought, heat treatable and cast aluminum alloys while providing an excellent base for subsequent painting or power coating services.

 

Aluminum Conversion Chromatization - Specifications

The two most common aluminum chromate conversion coatings certified are MIL-C-5541 and

ASTM B449. A summary of chromating services per the ASTM and MIL specs is as follows:

Aluminum Chromate Conversion Coating to MIL-C-5541 (MIL-DTL-5541)

Type I-Compositions containing hexavalent chrominum

Type II-Compositions containing no hexavalent chromium

Class 1A-For maximum protection against corrosion, painted or unpainted

Class 3-For protection against corrosion where low electrical resistance is required

Aluminum Conversion Chromatization to ASTM B449-93

 

Hexavalent Chromatization is a type of conversion coating used to passivate aluminum. It is primarily used for a corrosion preventive and paint bonding for liquid paint and powder coating . The process is named after the chromate found in the chromic acid used in the bath, more commonly known as hexavalent chromium.

 

Hexavalent chromium plating is the traditional method of chromium plating(most commonly known as chrome plating) and can be used for decorative and functional finishes. Hexavalent chromium plating is achieved by submerging substrates into a bath of chromium trioxide (CrO3) and sulfuric acid (SO4). This type of chromium plating provides corrosion and wear resistance, as well as aesthetic appeal.

 

Hexavalent chromium plating has its disadvantages, however. This type of plating produces several byproducts which are considered hazardous waste, including lead chromates and barium sulfate. Hexavalent chromium itself is a hazardous substance and carcinogen and is heavily regulated by the EPA. In recent years, automotive OEMs such as Chrysler have made efforts to replace hexavalent chromium finishes with more eco-friendly finishes.