tank model undercoats

In ww2 most everything for the Army came out of the factory painted olive drab. When it arrived in theater it was painted as needed. The primer coat and paints used on internal surfaces were close to green and/ or yellow zinc chromates. Duralumin was the most commonly used alloy at that time. It is fairly strong but is susceptible to corrosion. I suspect that you find pictures of corrosion if you use a search engine.

Thanks seasick

The M551 Sheridan saw service in the Vietnam war. I will find some original pics of it in action and see if I can see some evidence of corrosion.

thanks again.

Hi :

  Most corrosion of Duralumin was kind of like " Bubbles " (under surface corrosion  ) The scrapes and scratches would be a dull silvery color .Where you have the wearing away of paint from walking on it ,the color would be a dullish aluminium grey .

While bare aluminum is reasonably "shiny" when first exposed to air, it rapidly weathers to a flat sheen, and the color looses some of the "bare aluminum" look.  I often mix flat aluminum paint about 1:1 with a flat light gray to represent weathered aluminum.

I cant speak too much for firsthand experience with Sheridans. I saw plenty during my 3 NTC rotations in the 80, both OPFOR and OCs, some up close, but I never crewed on one. But I can comment on M113 family vehicles that I served on and was intimately familiar with in that time period. First off, the aluminum alloy armor does not show any corrosion. In most areas, modern mil spec paint is very tough and durable and does not chip, scratch, or wear off easily. There are exceptions to this, primarily on the sides of the hull where the track motion can wear away paint from debris alongside its path. Also on the bottom of the hull from bellying out over berms, stumps, etc. will abrade off much of the paint down there over time.  At least on older long serving vehicles. Now there will be signs of rust around bolt heads, as those are usually made from ferrous metals and not aluminum, but that would be best represented by a pin wash around those. For weathered Aluminum like Don is talking about above, Humbrol's shade of that color is beautifully "grayed" for that sort of stuff. Not bright like Tamiya or Testors.