wire arc spraying ZnAl coatings
02-18-2008, 03:55 PM,
#1
wire arc spraying ZnAl coatings
Hello, forum participants!
Hope everything is going well with you and your business!

I have two questions.
Whether will protect steel shipboard hull ZnAl coating (thickness: 0,2-0,25 mm), which is coated with using of wire-arc spraying method on ship bottom and shipboards, in marine atmosphere and sea water, if as a result of mechanical damage the coating area (1 m on 1 m) will be removed.
What will be better to protect in given situation ZnAl coating or AlMg5 coating?

Look forward to your early reply!
Thanks a lot and best regards!
Reply
02-18-2008, 04:40 PM,
#2
RE: wire arc spraying ZnAl coatings
Hi Technovel,

I'm not sure I fully understand your question re the damage to the coating area but in general, marine coatings are pure aluminium. AlMg5 is an expensive solution. The Mg is included to accelerate the corrosion rate of the aluminium do offer better protection early in the life of the structure. However, there have been cases where the acceleration does not stop and the aluminium is corroded away quicker than expected.

Zn/Al will not corrode as quickly as pure zinc but will be quicker than pure aluminium.

I would suggest you have a look at the relevant European standards for guidance on coatings in specific environments. BS EN ISO 14713 would be a good place to look. It will specify sealed zinc or sealed aluminium but general practice would normally be to use sealed aluminium. The thickness is dependent on the required life to first maintenance but 200-250 microns is a fairly thick coating that should give circa 20 years life to first maintenance.

Good luck,
Stuart Milton
Metallisation Ltd
https://www.metallisation.com
Reply
02-19-2008, 02:00 AM,
#3
RE: wire arc spraying ZnAl coatings
Hi Technovel

Sign0016 to the Surface Engineering Forum.

I tend to agree with Stuart, post above. As for the galvanic throwing power (capacity to protect adjacent uncoated areas) ZnAl and AlMg will lie somewhere between zinc (being highest) and aluminium. Suspect ZnAl will be higher than AlMg, but not totally sure. Zinc and aluminium have long and proven track records. ZnAl and AlMg are more recent and while accelerated corrosion testing predicts good behaviour, there is nothing like the real thing Happy0193
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