Aluminum vs Steel with ZnNi superficial treatment

Question

Aluminum vs Steel with ZnNi superficial treatment

Zz200 (Automotive)

(OP)

2 Jul 21 15:41

Hello everybody,

I'm new here. Hope to have exciting and useful conversations with you!

This is my first question:
Do you guys think it is safe to screw a M10 male made of Steel with superificial treatment of ZnNi into a screwboss made of aluminum?
The material of the screwboss (aluminum) cannot be changed. I could change the M10 male screw
I didn't chose that material but now I'm in charge of this project and I'm not sure about this compatibility...

Any advise or experience regarding this combination of materials?

Thank you in advance
Kind regards

CS

MintJulep (Mechanical) · Answer 1 · 2021-07-02 16:55:25

I think I would research an aluminum-flake coating (eg. Dacromet, Geomet) for the screw.

TugboatEng (Marine/Ocean) · Answer 2 · 2021-07-19 05:39:12

In general, steel and stainless steel screws with or without coatings are acceptable to be used in aluminum structures due to the relatively large size of the aluminum structure relative to the more noble fasteners. Outside of some very extreme conditions you shouldn't have any issue.

Zz200 (Automotive) · Answer 3 · 2021-07-19 06:24:13

Thank you all for the answers
Actually I'm talking about pipefittings... so a ZnNi Steel male fitting screwed into female cast aluminum...Im afraid it could cause intergranular corrosion and cause a leakage...

I found this document that explains corrosion:
https://www.faa.gov/regulations_policies/advisory_...

SOP is near so the team is not convinced there is enough time to do tests...

TugboatEng (Marine/Ocean) · Answer 4 · 2021-07-19 07:02:23

Is the corrosion potential from the interior or exterior? No fluid carried should be corrosive in an automotive application. External exposure can be problematic due to road salts but a gasketed connection can mitigate those issues.

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Aluminum vs Steel with ZnNi superficial treatment