Metal finishing Q&As since 1989



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How soon after casting aluminum should one paint the parts

We have aluminum parts die cast in China. Can they wait until they reach the United States to be painted, which is at least 4 weeks, but could be up to 6 weeks after they are cast? Naturally, we are talking the four seasons of weather, salty ocean, etc. Of course, these parts could then sit at the paint supplier for a few more days or weeks, depending on when they can fit them into their schedule.

If this is too long of a time period, what would be considered a more appropriate time frame? We need to make sure that our supplier in China gets these aluminum parts painted after they are cast, before too much oxidation occurs and reduces the quality of the paint coating.

Ric Oen
produce designer - Celina, Ohio, USA
February 2, 2011

As you appreciate the dangers of oxidation of the Al surface I think you have already answered the question yourself.

Terry Hickling
Birmingham, United Kingdom
February 2, 2011

I understand that time is important. However, I would like some sort of guideline(s) to make sure that the parts are painted within that time frame so that oxidation doesn't affect the quality and adherence to the paint.

Ric Oen
Engineer - Celina, Ohio, USA
February 4, 2011

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Whether it is 3 days, or 3 months, I would strongly suggest a pretreatment prior to painting aluminum, this would not only prevent the oxidation of the aluminum (which pretty much happens instantly after being exposed to atmosphere)but will also give you an excellent surface for paint adhesion.

Iridite (or chromate) is probably the best choice.

Marc Green
anodizer - Boise, Idaho
First of two simultaneous responses -- February 4, 2011

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Thinking of your problem it is my opinion that you import the items in their raw state... no pretreatment or painted.
Find a powder coating Co who can powder coat these items correctly. They should be able remove any Al oxide film; chromate or phosphate (my choice zirconium phosphate) and have good powder coating equipment and baking facilities.
If you contact me direct, I will supply a contact over there who may(?) advise you from a practical point of view as he had the same adhesion problems.
Terry

Terry Hickling
Birmingham, United Kingdom
Second of two simultaneous responses -- February 4, 2011