Aluminum metal pretreatment.

[dfarr67]

Metallurgy question, getting into powder coating and have a run of alum rims to do. Power washing most junk off before having sand blast done- but to halt alum from oxidizing and to prepare the surface directly for coating, what have you guys used in a similar situation?

[BCjohnny]

Chromating is the usual passivating pre-treatment for Aluminium

It's not always completely successful at preventing skinning

[hoodeng]

Check with your platter, they usually do the pre-treatments themselves, or will inform you on how they want the job presented.

Cheers.

[dfarr67]

Thanks for the replies, situation is small town alberta so shipping is an issue with many usa products simply not available or uneconomic. Still need to visit napa and a northern metallic location.
Ideal parameters would be a safe solution to apply by spray directly after blasting at room temperature and allowed to dry, some products I have been looking at- but may be more geared towards ferrous:

POR-15 Metal Ready
Ospho
Picklex-20 ($$)
Guardian Chemicals- Flashguard 1/100 dilution($450/5 gal- but they will break down to gallon for me)
Still researching

[David Redszus]

Thanks for the replies, situation is small town alberta so shipping is an issue with many usa products simply not available or uneconomic. Still need to visit napa and a northern metallic location.
Ideal parameters would be a safe solution to apply by spray directly after blasting at room temperature and allowed to dry, some products I have been looking at- but may be more geared towards ferrous:

POR-15 Metal Ready
Ospho
Picklex-20 ($$)
Guardian Chemicals- Flashguard 1/100 dilution($450/5 gal- but they will break down to gallon for me)
Still researching

Correct procedure for protection of aluminum surfaces involves proper cleaning and corrosion protection
prior to powder coating.

First remove all dirt, oils and greases from aluminum surfaces. Remove all paint and bondo.
Blasting can be used to obtain a smooth surface. Sand blasting will produce a matte dull finish with an
excellent surface for coating adhesion. Glass bead will produce a glossy, but not mirror, finish.

Apply Alodine 1201 per details shown below. This can be performed in your own shop.

Keep the surfaces clean prior to powder coating.

Alodine 1201
Detailed Product Description:

Alodine® 1201, a registered trademark of Henkel Surface Technologies, is a chemical
treatment process for aluminum used to provide corrosion protection and as a surface
preparation for paint and adhesives. Sometimes called “aluminum passivation,” it
contains hexavalent chromium and is intended to provide corrosion prevention even
when left unpainted.

Chromate conversion is an excellent treatment method to prep aluminum prior to paint
or adhesives since it greatly enhances the ability of an organic coating to form a bond
with the aluminum substrate. Being a surface conversion treatment rather than a coating,
it will not alter the dimensions of the part.

It is frequently used on electrical and electronic equipment because it provides increased
corrosion resistance while remaining electrically conductive.

The Alodine process produces a microscopic thin film commonly prescribed on aluminum
to provide the following surface characteristics:
High-adhesion surface preparation for paint
Improves corrosion resistance
preserves electrical conductivity of surface
No change in dimensions

Specification & Certifications:
Alodine 1200 methods and properties are defined by Mil-C-5541-F (Now AMS-C-5541)
and AMS-A-2473.

Application Notes:
The best results are achieved on wrought alloys (machined billet aluminum alloys).
Good results can also be achieved on type 356 aluminum castings. Type 380 die
casting alloys do not alodine well, however. It should also be noted that the
chemical film is fragile immediately after processing and a 24-hour waiting time
before handling the parts is preferable.

Applications in which temperatures can reach over 120ºF can break down the corrosion resistance
of the coating. In comparison to anodizing, this chemical film is more fragile and
not generally recommended for high-use area. This is a visible coating that leaves the surface with
a golden coloration. Also available in a clear formulation.

Surface Preparation:
Aluminum surfaces must be cleaned with a suitable etchant such as Alumiprep 33
or Metal Prep 79, followed by a water rinse.

Immersion Process:
To formulate bath, mix 33 parts Alodine solution with 67 parts of water. Immersion
time is 2 to 5 minutes. Application temperature can range from ambient up to 100ºF.
Rinse part thoroughly with water and allow to dry. Surface is ready for paint.

Brush-On Process:
Alodine solution may be applied by brush or sponge, by using undiluted directly from
container. Assure surface remains fully wet during required contact time of 2 to 5 minutes.
Rinse part with water and surface is ready for paint. 1 quart treats about 100 sq. ft.

[BCjohnny]

dfarr67

A lot of pre-treatments sold simply don't work

Two decades ago I had a manufacturer come to me with, up to that point, an incurable corrosion problem ...... powdercoated Aluminium castings ...... when just using the traditional pre-treat methods

They'd pass 'salt spray' etc, but wouldn't survive without shedding in the real world

Only by looking at the whole process again did I manage to get the items to live out the warranty ..... the answer didn't use any chemicals at all

[dfarr67]

That Alodine and several other chems are nasty stuff. It is available in Canada, $cdn130 shipped for 1 gallon. Does it perform? Anything that would work well for ferrous/non ferrous to cut down on chemical stock?

https://www.aircraftspruce.ca/catalog/c ... ne1201.php

I think the surface texture after blasting would be sufficient to hold powder, it's just the gap between fresh blasting and coating whether steel or alum that has me thinking of a preservative that you don't need to wash off. Idea was to have the blaster to apply light mist immediately after stripping.

[David Redszus]

That Alodine and several other chems are nasty stuff. It is available in Canada, $cdn130 shipped for 1 gallon. Does it perform? Anything that would work well for ferrous/non ferrous to cut down on chemical stock?

https://www.aircraftspruce.ca/catalog/c ... ne1201.php

I think the surface texture after blasting would be sufficient to hold powder, it's just the gap between fresh blasting and coating whether steel or alum that has me thinking of a preservative that you don't need to wash off. Idea was to have the blaster to apply light mist immediately after stripping.

Blasting will remove surface debris but will not remove junks from micro cracks and pits.
Alodine is safe to handle; we use it very frequently. Just don't drink it or wash your face in it.

[dfarr67]

What is the viscosity like for the Alodine?

[David Redszus]

What is the viscosity like for the Alodine?

It has the viscosity of water.

[BCjohnny]

I think the surface texture after blasting would be sufficient to hold powder, it's just the gap between fresh blasting and coating whether steel or alum

Yes, not so much steel but certainly Aluminium, and ultimately governs whether the paint stays stuck ..... or not

[dfarr67]

This was also suggested. Started out promising- but it looks like it requires a rinse- which is an issue for me due to water quality.

http://pantheonchemical.com/prekote-sur ... treatment/

[BCjohnny]

The 'problem' is as a small scale industrial user of chemicals it rapidly begins to make little sense from a cost / compliance point of view ...... and if you think it's tight now just wait a few years

You don't put a figure on your 'run' of Aluminium wheels

If it's a few sets, pick an off the shelf product that best suits your liability and pocket and call it good ...... or check online as there are numerous 'recipes' for passivating solutions you can put together yourself (usual caveats apply)

If it's an ongoing venture then there are other ways it can be done, more initial thought & outlay but better in the long run

I'm well out of it all now, but if you need anything specific you're welcome to PM me

[hoodeng]

When you said, 'getting into powder coating' did you mean you are preparing batches for someone else to coat? or have you bought a powder coating system, ovens etc?

[dfarr67]

I purchased an oven and the basics years and years ago and it's been sitting in a corner, big enough to do a harley frame and maybe a few rims at a time. Locally there is demand and maybe later ceramic coating as well. Hopefully more a hobby that pays for itself. And yes buying the supplies at my scale is expensive. I don't and won't be doing sand blasting myself.Ordered a gallon of Anolind 1201, wand to get something for ferrous as well, flashguard or ospho- choices are very limited these days.