I am investigating the feasibility of bringing a powder coating operation in-house to coat aluminum parts. We currently outsource this activity. Does this process need a chromating operation or can it be phosphatized. Can you tell me the pros and cons associated with each? S.M.
Aluminum parts can be cleaned with either a chromate conversion coating process or an enhanced iron phosphating process. However, only a chromating or non-chrome aluminum pretreating process will provide additional corrosion protection under the powder coating. So it becomes a question of how much corrosion protection do you want for your product? Cleaned and powder coated aluminum will probably give you 1,000 hours of salt spray protection, where a chromate or non-chrome aluminum pretreatment will provide up to 5,000 hours of salt spray protection. Understanding your product’s coating performance requirements and customer expectations will go a long way to ensuring that you wisely select the appropriate technology for your product.
As for the Pros and Cons, iron phosphate can be disposed to drain without wastewater treatment in most parts of the United States (Pro) but cannot provide the protection of chromate or non-chrome substitute aluminum pretreatments (Con). It is just the opposite for chromate conversion, it must be cycled through a wastewater treatment system before dumping to remove the chrome (Con) but provides superior corrosion protection (Pro). Of course, if you use the non-chrome aluminum pretreatments or chromate replacement technologies, you get the corrosion performance without the wastewater problems (both Pros).