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Galvanic corrosion in new product

Galvanic corrosion in new product

Galvanic corrosion in new product

(OP)
I've started a small design company, and I have 3 corrosion questions on my first product.  

It is a mechanism about 1/2 the volume of a can of Coke.  The parts are made of the following materials:
1)  260 Brass
2)  410 Stainless, powdered metal, 85% density
3)  several different polymers
4)  Copper (nearly pure), powdered metal, 94% density
5)  Aluminum (Al 91.5%, Cu 2.5-5%, Mg 0.2-0.8%, Si 0.5-1.2%), powdered metal, 90% density.

The working environment is indoors in a non-air-conditioned room surrounded by normal, breathable room air.  At times, the ozone concentration in the room may be higher than normal.  

My questions are:

1.  My understanding is that, in the environment described above, ordinary 410 stainless can develop surface corrosion but that the corrosion will not go beyond the surface layer.  Dark spots can appear on the surface, but progressive oxidation and disruption of the surface finish will not happen.  Is this also true for an 85% density sintered powdered metal version of 410?  

2.  Because the equipment is not designed to be run in wet environments, much less in seawater, I was not worried about the materials relative positions on any of the galvanic series.  Recently, an associate advised me that I should be concerned about galvanic corrosion, especially given the higher than normal ozone concentration.   I just don't know how to evaluate this.  Should I be concerned about galvanic corrosion under these circumstances?  

3.  Aluminum's "self-healing" oxide layer protects the sub-surface from corrosion, although I believe this is more true for pure aluminum metal than most of the alloys.  I have seen mechanical mechanisms made of aluminum or an aluminum alloy that have stopped working because of an excess of corrosion.  The aluminum surfaces can become very rough, and a white hard powder forms.  Would someone tell me how to select an aluminum alloy so that it will not corrode in the environment I've described?

I appreciate any light you can shed on these questions.  Thank you very much!

Dave
  

RE: Galvanic corrosion in new product

(OP)
I'm sorry, I should have mentioned that the fastening used within the product was a combination of:

1)  302 Stainless screws,
2)  Press fits (interference fits),
3)  Cyanoacrylate adhesive on sliding fits

Thank you!
Dave

RE: Galvanic corrosion in new product

Is there some sort of lubricant(s) circulating within this mechanism, or at least coating the various parts?  If so, then galvanic corrosion may not be of much concern.  If not, then it could be.

RE: Galvanic corrosion in new product

(OP)
There are no lubricants in the device.  There's only one moving assembly, and it's interface is 410 SS sliding on brass rod bearings.  Velocities are small, as are forces.  My customer asked for no lubes: the environment tends to be dusty and servicing these devices is problematic.  

Thanks very much,
Dave

RE: Galvanic corrosion in new product

You would need an electrolyte for galvanic corrosion to be an issue.  The higher ozone levels could lead to more surface corrosion on some of the parts such as Al and even the polymers.
You might consider a dry film lubricant.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Galvanic corrosion in new product

(OP)
Do dry film lubes last very long?  I've used molybdenum disulfide based lubes in the shop, but I don't really have a good idea of their longevity.  Are they easily scraped off by sliding action between two parts?

Dave

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