AAMA Specifications for Steel

Q. We manufacture steel and aluminum outdoor products. Do the AAMA powder coat specifications for extruded aluminum—AAMA 2603, AAMA 2604 and AAMA 2605—correlate to the application of steel materials? If so, are there any metrics for how similar powder coats will react differently on steel? A.J.

A. The AAMA (American Aluminum Manufacturers Association) specifications cover many different initial and long-term performance requirements, as well as pretreatment requirements for aluminum and test methods for the finished product. One key element is outdoor weathering measured by gloss and color retention. Those items could apply to a finish applied over steel. Dry adhesion, hardness, initial gloss, impact, nitric acid, window cleaner and a few other tests that relate to the endurance of the coating on the outside surface also would be similar with steel.

However, some of the performance criteria would not fit with a steel substrate, and the pretreatment would be different for steel. Corrosion requirements, for example, are 3,000 hrs of salt spray for AAMA 2604 and 4,000 hrs for AAMA 2605, and the numbers are similar for humidity. That will be hard to achieve on steel without a primer and may still fail, depending on the quality of the surface treatment. Film thickness with steel should be heavier in general. A good aluminum conversion coating will create an excellent bond with the powder coating, and as long as the film is complete, the penetration of moisture will be limited and corrosion protection will be quite good. Steel is more vulnerable to moisture penetration and corrosion, and a thicker film is typically needed to get the same level of protection from failure.

In general, you could adapt the AAMA specifications to fit steel. However, if you want to develop a specification for steel, you should visit the Powder Coating Institute website (powdercoating.org) and click on the small red button at the top right labeled “project SOS”. It will allow you to select the environment your product will be subjected to in the field and the substrate, and then define a performance level and the needed process to achieve it.