Marine Anodising

So what is marine anodising?  It is the same as standard anodising except that the specified coating thickness is 25 microns with a minimum coating thickness of 20 microns.  For some marine grade anodising the coating requirement will be greater.

For most water based applications a standard marine coating thickness of 25 microns is all that is required.  For application that involve extreme/constant exposure to for example salt water then a hard anodised finish or other coating option may be considered.

Choice of alloy

Certain alloys of Aluminium are more resistant to corrosion than others and are therefore more suited to marine applications, while other alloys would certainly be a poor choice.  The best alloys for corrosion resistance are those found in the 5000 series of alloys, followed by those in the 6000 series.  A poor choice for corrosion resistance are the 2000 series of alloys and this is due to their high copper content.

Choice of coating

If the parts only have limited salt water exposure or only indirect exposure, then standard marine grade anodising will be suitable.  The advantage of this is that you still have available the full range of exciting anodised colours.  Here is an example of a company using standard marine grade anodising for their product range;

For parts that have more continuous exposure to salt water then either hard coating or other coating options need to be considered, however for most applications standard anodising will give excellent results.

Please be aware that no matter what the coating is, salt water is extremely corrosive and it will eventually work its way through a coating causing corrosion damage.  So the coatings must always be correctly looked after;

• Always rinse off any salt water after use
• Clean only with non-abrasive and neutral detergents
• Avoid scratching the coating as this opens a pathway for corrosion
• If corrosion does begin, get it seen to as soon as possible before any major damage is done.  Anodising can easily be re-done.  Below is an example of pitting corrosion showing the devastating effect it can have on an item -

This  particular part is of a bilge pump.  The part on the initial inspection only showed minor surface corrosion and discolouration.  A light bead blast removed all the soft corroded areas highlighting the true extent of the corrosion.  The pitting corrosion is quite extensive and in some spots has travelled almost all the way through the metal.