Powder coat paint?

[model 10]

In the 80’s I dove on a WWII Japanese bomber in Truk Lagoon which had been underwater for 40 years. The skin was bare anodized aluminum. It was in amazingly good shape. 40 years in salt water. That’s good stuff.

Sunspot Baby[/QUOTE]

I think that the material you saw underwater was an Alclad type aluminum. A pure layer of Al on top of the alloy. This is the most common material for aircraft sheet. You would not have had anodized aircraft skin back in those days. Some of what you see these days is an alodine treatment, it sometimes looks similar.
Every time I look at our genoa track I am amazed at how well good anodizing is. Powder coating would have failed right away. I had our boom powder coated by a non aero space quality shop and it has failed badly in 5 years.
Powder coating has it's place as does anodizing. Not many places have shops to anodize and doing it yourself with some dye and acid does not give you a very good surface. There are half assed powder coating shops all over now..

[a64pilot]

FWIW, I manufacture crop dusters, Thrush Aircraft to be precise. Corrosion protection is more important on a crop duster than any other aircraft except maybe for a float plane kept in salt water. The airframe is 4130 chrome moly tube steel and has been for the last five years or so powder coated as powdercoating gives vastly superior corrosion protection than wet paint on steel parts. Powdercoat can be touched up with wet paint.
Anodizing is a very good corrosion protection for aluminum but is rarely seen on aircraft due to it changing the physical properties of aluminum. Usually aluminum is alodined, we alodine every aluminum part on a Thrush and then paint it.
The material is very important in choosing which method for corrosion protection, you can't anodize or alodine steel of course, steel you cad plate. I've had very good luck with powder coating steel, maybe not so much for aluminum though.

[model 10]

Spreading Sulfur is the worst. Good thing we don't have sulfurous seas.