Aluminum alloys that will corrode imperceptibly in industrial or marine environments are 5005, 5050, 5052, 5086 alloys 1100,3003,3004,6061-T4&T6,6063-T5,Alclad2024-T3 corrode somewhat more but work satisfactorily. (1)
Anodic coatings of 0.4 to 0.7 mil and greater are used to protect aluminum 0.7 mil and greater would be best for a gutter interior
Paint coatings of vinyl, urethane, laquers and etc. are available for aluminum, chemical etches usually improve adhesion of these coatings.
Test results simulating your environment should be reviewed, ANSII and DIN tests are available for exposure simulation.
Some gutters may have some super coating on the outside but what about the inside?
Poorly designed or maintained roll forming equipment may damage a coating, check before accepting material.
Vinyl can be made soft and pliable or hard and rigid. Most vinyl gutters are made from UPVC or un plasticized semi rigid Poly Vinyl Chloride (PVC)
Additives for UV (ultra violet) protection are critical for PVC, Ti02 (titanium dioxide) is normally used to protect PVC and sufficient quantities are necessary for protection.
Coatings and capping can be used to protect PVC. Vinyl, ABS, Acrylic and other caps can be thermally fused to the PVC surface. Acrylic may give the best protection as it reflects solar energy and prevents heat build up.
Paint is effective protection but should be evaluated for heat build up and changes to impact resistance.
Testing should be evaluated for weathering, both ANSII and DIN tests are designed to simulate weathering effects on vinyl.
Electro plating, hot dipping, and cold galvanizing are available to coat steel with a corrosion inhibiting zinc layer.
Zinc coatings should be thick enough to offer long term protection.
Tests are designed to simulate long term exposure to marine or polluted environments.
When repairing or assembling gutter choose a binder that does not destroy the zinc coating.
Painting galvanized gutter normally requires surface preparation (mild acid wash, ie. vinegar) to ensure a good bond.