Looking for Common RoHS Compliant Base Coating for Cast A360.0 1

[MadMango]

Currently we polyester powder coat our cast products that are made of A360.0. These are typically housings for electronics, with an outdoor rated service life of 7-10 years (96hr salt spray). We are investigating some form of "base coat" that will cover the entire part for corrosion purposes and allow us to powder coat only the exterior surfaces for customer requirements. I am only familiar with anodizing (AMS 2471 and 2472), and chromating (AMS-C-5541). I have found a RoHS compliant specification for a chemical film, MIL-DTL-5541, Type 2 (hex free chromate).

My question is if this is the most commonly sourced RoHS compliant coating for corrosion resistance, or is there something else available out there that I haven't come across yet? Any information and discussion is greatly appreciated.

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[CoryPad]

For aluminium alloys, you are looking at the three most common surface treatments for corrosion resistance: anodizing, inorganic pretreatment, and organic coatings. For pretreatments, modern ones are hexavalent chromium free or even free of all chromium. One particular product is Henkel's Alodine 5200.

 

[drawoh]

MadMango,

I have been calling up CHEMICAL FILM ROHS COMPLIANT.

The chemical films are equivalent to MIL-5541, but they do not contain hexavalent chromium.

--
JHG

 

[MadMango]

Thank you. Any feedback if the hex free coatings will survive 96hr salt spray? Every site I have reviewed says it is dependent on the alloy, but none give A360.0 as an example.

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[TVP]

A360.0 is an alloy for high pressure die casting, which means that corrosion performance will be dictated by how well the surface is cleaned to remove the lubricant/release agent used during the casting process. If you can find data on A380, this alloy will be similar. Well prepared surfaces with Alodine 5200 should be able to meet the 96 hour requirement.

 

[KENAT]

MM, not sure about the salt spray but for parts that need to be ROHS compliant & electrically conductive after chem film we've been using this call out for several years.

"FINISH: CHEMICAL CONVERSION COATING PER MIL-DTL-5541F TYPE II CLASS 3 (CLEAR)."

It's been a while since I read the std but as I recall this note calls out the ROHS compliant [type II] 'thin' (low resistance) [class 3) 'flavor'.

I'm guessing you'll want class 1A if you choose to reference this std.

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