Galvanic compatibility of metal fasteners in carbon composite

[20vt]

Hi all,

newbie here, I stumbled across this site looking for some information on galvanic compatibility so I thought I may as well ask my question directly.

I have an sports automotive application where temperature and weight are key issues

The structure is a mixture of corrosion resistant steel and titanium on to which we currently attach a titanium plate using Zn/Ni coated steel fastners.

We need to switch to a carbon composite to save weight.

We are getting galvanic corrosion of the zn/ni steel fasteners (316), no surprise.
I'm recomending switching to Ti fasteners or other options of switching to fasteners of passive steel, eg A286, AM350 AM355, which are all going to cost.

my questions are:
1. Are there any coatings I can apply to a steel fastner to prevent corrosion with Ti and more importantly CC.
2. Can anyone suggest a more suitable fastener material?

 

[CoryPad]

Zn/Ni coated steel fastners

zn/ni steel fasteners (316)

These two statements are confusing. Can you reply stating exactly what your joint components are (in order)?

The problem with fasteners and coatings is that the coatings need to be thin to prevent thread fill and underhead creep. Thin coatings aren't great barriers.

You are likely to have best performance (at high cost) with fasteners like Ti, A286, or MP35N. If you must use carbon-steel fasteners, perhaps a nonmetallic coating on the fastener will be better (although organic coatings can be damaged fairly easily). Zinc/organics, electrocoating, and PTFE-based coatings are options.

http://www.doerken.com

http://www.themagnigroup.com

http://www.ppg.com/car_indcoat/pretreats18.htm

http://www.whitfordww.com/products.cfm?productnameid=120&id=21

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[20vt]

Cory,
Thanks for the reply.

Sorry for my lack clarity.

The construction is currently
1. Organic top coat
2. 2 inspection panels one Ti 64 panel and one 316L stainless panel
3. Electro-deposited alkaline Zn/Ni plated carbon steel fastener.
4. Ti 64 and 17 4 PH steel structure.

We want to replace 2. 316L with carbon composite, and move to;
1. Organic top coat
2. 2 inspection panels one Ti 64 panel and one carbon composite panel.
3. Electro-deposited alkaline Zn/Ni plated carbon steel fastener.
4. Ti 64 and 17 4 PH steel structure.


As stated these are sports auto near engine, so temp and mass are an issue. Also we race in Europe so Cd and Hex Chrome are out.

Can't change the structure to 100% Ti due to fabrication issues of Ti. Can't change the panels, so we are looking at modifying the fastener material and/or use a coating.

I am recomending a switch in fastener materials to Ti, but there are cost implications also inspection panels are removed so galling is also a consideration.

thanx

 

[TVP]

Titanium fasteners are the default choice when joining to carbon composite structures. Galling can be managed (somewhat) by use of lubricants/coatings. I recommend contacting Steve Buzolits at SPS to discuss their Aerlite Ti fasteners and options for reducing/minimizing galling. Use the following link for more information:

http://www.spstech.com/cgi-bin/aero...t_engineer&function=display&branch=jenkintown