Metal finishing Q&As since 1989

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A-380 Finishing Options for L.E.D. Emergency Lighting

2003

Hello to all,

My name is Greg Pederson and I am the Director of Engineering for a company that manufactures L.E.D. based emergency warning lights (like the kind found on police vehicles). All of our products are of an Aluminum (6063) extrusion based chassis design, and are always clear or black anodized. We have found this to be a happy marriage and to date; we have suffered no finish failures. We are currently developing a new 360-degree warning light and I am electing to use A-380 die cast alloy (due to the complex geometry). We are exploring the various finishes available and as I have had no experience with finishing A-380 I would be grateful for any assistance. This is an outdoor product operating on such vehicles as snow plows (salt!) trash trucks, and police motorcycles. Main concerns are

1) Corrosion from salt.
2) UV fading over time.
3) Pealing or delaminating.

Has anyone found a cost effective way to anodize this material? (Our part production is projected in the neighborhood of 10-15K units/yr). How well does e-coating or powder coat paint hold up?

Thank you for your considerations in regards to my plight :)

Greg Pederson
- Saint Cloud, Minnesota, USA

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Sulfuric acid anodizing can be used successfully on die cast alloys like 380/A380. Chromic acid baths cannot. As always, surface preparation is important. Die lubricants must be removed from the as-cast surface. Subsequent sealing of the anodized layer provides enhanced corrosion protection.

Electrocoating and powder coating are both suitable for enhancing corrosion protection, especially over an anodized layer. Phosphates and other pre-treatments can also be used. Electrocoating almost always involves epoxy based resins, which have poor UV resistance. Powder coating is more common for exterior applications, with the added benefits of color choice, fade resistance, etc. Check out the websites of automotive paint vendors for more information.

Toby Padfield
- Troy, Michigan
2003

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The previous answer is best. Powder Coating is the way to go for maximum corrosion protection.

380 is very difficult to anodize because you anodize ALUMINUM. The silicon on the surface does not "anodize", it just turns ugly gray color. Thin walls in 380 casting have more silicon on the surface than thick walls. There are several "dips" recommended in our industry for removing "most" of the silicon from the surface, none are 100% effective. Your anodized 380 castings will never look as good as you are used to seeing on the wrought 6061.

Let us know if you still want more detail information on the surface preparation of 380 die castings.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2003