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Powder Coating Process reduces Ultimate Tensile Stregth

We are working one of the projects in India where we use Aluminum clamps of Alloy 6082
and found that Aluminum after undergoing the Powder coating process has a reduced Ultimate
Tensile strength by 20%.

Could somebody explain why the strength of Aluminum reduces when it udergoes powder coatign process.

Syed Ahmed
Buyer - New Delhi, India
October 6, 2009

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Sounds as though your curing temperature for the powder coating is high enough to over-age the aluminium. What temperature do you heat it to for the powder coating? Is your aluminium heat-treated to temper T4, T6, or T651?

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
October 7, 2009

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First of two simultaneous responses --

The powder coating is baked on, meaning that the parent metal is subject to a heating and cooling cycle. I would expect that the cooling cycle is slow, which would allow for larger grain structure in the metal. Larger grain means lower initial tensile strength (but also more ductility).

Kevin Hawkinson
- Seattle, Washington, USA
October 8, 2009

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Second of two simultaneous responses -- October 8, 2009

Mr. Syed, Aluminium alloy 6082 is a medium strength alloy with excellent corrosion resistance. It has the highest strength of the 6000 series alloys. Alloy 6082 is known as a structural alloy and is gaining popularity in the U.S.

There are two potential reasons I could imagine. One is that you are improperly measuring the tensity strength. Let's assume your correct in your measurement.

The second is that 6082 is a heat treatable alloy. This means that in areas that might get welded or exposed to heat, the elasticity and tensile strength will be less or reduced. Powder coating is cured at various temperatures by the various companies. There generally (3) curing schedule for high temp powder.

They are:
395 degrees for 15 minutes
375 degrees for 20 minutes
350 degrees for 25 minutes

Generally, the powder manufacturer will provide a product specification sheet that will help you with the cure schedule.

I would try all 3 of these cure schedules and test after each one to see if the heat is the culprit.

Bob Utech
Benson, Minnesota