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Magnesium Elektron Patented alloys such as Elektron 43 have inherently good general corrosion resistance (typically <30mpy). However surface protection is required for improved performance and also to mitigate against galvanic corrosion.
A typical corrosion protection scheme for magnesium alloys:
- Chemical conversion coating
- Plasma Electrolytic Oxidation (PEO)
- Powder coating
- Sealer (only PEO)
- Galvanic protection:
- Aluminium alloy washers
- Aluminium alloy anodised shims
- Polymer coated washer
- Plastic washer
Due to current and anticipated environmental legislation that restricts the use of hexavalent chromium chemicals, all treatments and solutions proposed are REACH compliant (Registration, Evaluation, Authorisation and restriction of Chemicals).
Theses readily available options have been deemed most appropriate:
- Chrome free pre-treatments
- PEO coatings
In all cases it is crucial that adequate cleaning is carried out to ensure that the top coat has sufficient adhesion and performance. Cleaning should include the following steps:
- Alkaline degreasing
- Rinsing (best practice is DI water)
- Acid etching
- Rinsing (again, best practice is DI water rinse)
From our evaluations, the best performance of the recommended conversion coating have been obtained when sufficient cleaning, using the steps detailed above has been carried out.
Cleaning helps with the corrosion protection and adhesion performance of the surface protection system. i.e. helps to avoid delamination and poor performance of the top coat.
Powder coatings proved to be suitable are hybrid epoxy/polyester. Magnesium Elektron has identified a number that comply with the following:
- FAR 25.853 (a and d)
- ABD0031-(Sections 7.3/7.4)
Due to Magnesium and its alloy position in the electrochemical series careful of consideration is required when dissimilar metals are used in intimate contact. While surface treatments and coated fasteners are important but it is equally important to consider how design and layout of the components might reduce the exposure to galvanic attack.