Q. I wish to powder coat a part that is die cast aluminum used for exterior luminaire housings. The surface will reach around 200 degrees C during use. In the past I have seen many similar products with corrosion and paint peeling or blistering. My question is can you explain the basic processes prior to coating and do I need to specify a special powder or are all powder coating materials rated for the same temperature in use? Many thanks. P.G.
A. Aluminum should be cleaned to remove any grease, oil or shop dirt. The surface must be free of all contamination. After it is clean you should pretreat the surface with an aluminum conversion coating. Chromate or a non-chrome treatment will do. These products are usually applied in a multi-stage process with cleaning, rinsing and treatment in a spray tunnel. The treatment prevents the corrosion and coating failure you describe. Be sure to get the coating on heavy enough to provide good protection. The use of a primer will enhance performance on outdoor products. The temperature is not a problem for many powder coatings but there are some high-temperature products that may be helpful. If the product will be exposed to sunlight the chemistry should be a polyester resin to avoid rapid fade of the finish.