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What lab analysis will help fix our aluminum substrate problems?

Good morning
Hi again, I want to know which type of lab analysis we would do to our pieces,
we are having problems when we apply powder paint, the pieces look like if they have silicone. And other pieces look like they have a black powder (we think this is graphite, because the pieces are extrusion).
I want to know exactly what compounds have those pieces ( I mean if the powder is graphite and if the Al casting has silicone).
I asked to the supplier and they said they don't use silicone..

Regards from Mexico!

Victor Kuznetsov
Paint Process Eng. - H. Matamoros, Tamaulipas, Mexico
November 20, 2009

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November 30, 2009

Victor

Silicon (the element Si) will be found in some many aluminum alloys. Silicone is a fantastic release agent and should not be present unless you have surface contamination. Key to good coatings application is always cleanliness of the surface. I would check your cleaning process.

Terry

Terry Tomt
- Auburn, Washington, USA

I think this is your 3rd posting on the same subject and I would suggest that you supply some of the images of the powder delaminating on your fitting which may help in obtaining some feasible responses'. Knowing a little more about your problem than your post shows here... aluminium sections welded to a base casting, I would enquire what GAS is used in the process of welding together the extrusions and the Al casting?

Terry Hickling
Birmingham, United Kingdom
November 30, 2009

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1.- Let me try to explain all the process first.
Our main product are lighting poles.
We cast the base and buy the extrusion. The casting alloy is 356 and the extrusion 6061, an important note (the thickness difference is something more than a half inch).
Then we weld them with Al welding wire, the gas is Argon. The we send the pieces to a 5 stage pretreatment (alkaline degreaser-rinse-IRON PHOSPHATE (on aluminum? I working to change into a new process)-rinse-seal.All by immersion tanks (because the material size). Then load it to the paint rails. PREHEAT (I'm investigating why we preheat Al material until 300° F, when you apply the paint is almost cure), paint and cure.
Yes is my fifth post in here; so here are pictures:

 

Victor Kuznetsov
- H. Matamoros, Tamaulipas, Mexico
December 4, 2009