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Alodine treatment to Mil-C-5541 Class 3 on cast aluminium parts, AlSi10Mg T6

January 21, 2010

I am in the need of information about Aludine 1200S chromating treatment, on chill cast aluminium, like AlSi7Mg T6 and AlSi10Mg T6, to achieve the requirements in MIL-C-5541 [affil. link or DLA] Class 3 standard as follows:
Electrical resistance not to exceed 5 milliohm/sq.inch before salt spray exposure (168 hours in 5% salt fog and 35 degrees C), and not to exceed 10 milliohm/sq.inch measured after the salt spray exposure. The resistance is measured with a pressure of 200 psi to the surface.

I think about concentration of fluid, temperature of fluid and holding time

Thanks in advance

Best regards,

Dag Leon Ilestad
Buyer - Arendal, Norway

January 22, 2010

I have never worked with your alloy, so can not speak from experience with it.
I would definitely Contact the european branch of the folks that make Alodine that you propose to use for help on the preprocess procedures as well as the Alodine step.

I see a couple of potential problems. The high silicon content is probably going to require a fluoboric acid etch step. This acid will fairly uniformly attack the silicon and the aluminum and will aggressively attack the MG, so time temp and concentrations are probably going to be critical. Also the cleaning step probably should be a non etch type or you will remove a lot of aluminum relative to the Si and Mg, so it will not take the Alodine step very well.

It is probably doable, but it will require closely following the process steps that you find that work. As the tanks age, parameters will probably shift slightly.

Lots of work for this alloy versus a mostly Al alloy.

James Watts
- Navarre, Florida

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