Filiform Corrosion of Coating on Aluminum Structure

Material
3004 aluminum alloy in the H291 temper.

Environment
Exterior of vehicle driven on the prairies.

Background
Since Testlabs International had analyzed coating failures of the one-coat system used in the past, the company implemented a two-coat paint system for the aluminum sheets.

Service Life
Ranged from five to eight months.

Findings
The two-coat paint system, which specifies a total dry film thickness of 1.1- 1.3 mils, has reduced the number of corrosion sites as compared to the one-coat paint system.

With the one-coat paint system, there were 100+ corrosion sites / ft2

With the two-coat paint system, there are five to 17 corrosion sites/ ft2