Are special bolts really needed to prevent corrosion to aluminum?

stevenlee · 3 November 2006

The NSX uses specially plated steel bolts to prevent corrosion to the aluminum on the car. I know that many people use standard zinc plated bolts when when modifying or adding after market parts.
Does anyone know how critical it is to use only Acura special bolts?
Has anyone ever experienced corrosion problems from using zinc plated bolts?
I have heard that Stainless Steel bolts are OK. Does any one know if this is correct?

scorp965 · 3 November 2006

Zinc and aluminum are close together on the galvanic scale, the closer together the two materials are the less chance there is for corrosion. Stainless steel and aluminum are far apart, so stainless steel is not an ideal choice, unless coated with Zinc. You should have no trouble using generic zinc hardware, but I would stay away from non-plated stainless steel.

Hugh · 3 November 2006

Depending on the part being bolted on why not use aluminum fasteners? Zinc would be the next best choice. The Honda "special bolts" are coated in Dacro which is made primarily from zinc and aluminum.

"The Dacrodip solution is a dispersed aqueous solution made from metallic zinc and aluminum flakes, chromic acid and glycol etc. For coating, the duly cleaned components are dipped into it and any excess solution is removed by spinning. Then the components are heated to about 300 deg C in an oven in a closely controlled atmosphere. The hexavalent chromium gets reduced to trivalent chromium i.e. an insoluble amorphous oxide. This acts as a binder for the many overlapping flakes of zinc and aluminum to form a film. At the same time the chromic acid in the solution also reacts with the substrate forming a chemical bond providing a strong adhesion."

ediddynsx · 3 November 2006

Hugh said:
Depending on the part being bolted on why not use aluminum fasteners? Zinc would be the next best choice. The Honda "special bolts" are coated in Dacro which is made primarily from zinc and aluminum.

"The Dacrodip solution is a dispersed aqueous solution made from metallic zinc and aluminum flakes, chromic acid and glycol etc. For coating, the duly cleaned components are dipped into it and any excess solution is removed by spinning. Then the components are heated to about 300 deg C in an oven in a closely controlled atmosphere. The hexavalent chromium gets reduced to trivalent chromium i.e. an insoluble amorphous oxide. This acts as a binder for the many overlapping flakes of zinc and aluminum to form a film. At the same time the chromic acid in the solution also reacts with the substrate forming a chemical bond providing a strong adhesion."

Damn! I guess someone got an A in chemistry :wink: :tongue:

Bob Kenney · 3 November 2006

Do NOT use aluminum bolts in an aluminum tapped hole without liberally coating them with Anti-Seize compound.

Aluminum and Stainless are both prone to "Galling" when assembled with a nut or in a tapped hole of the same alloy as the bolt. If galling occurs it creates what is known as a "roller" between the threads of the bolt and the nut. This roller will increases in diameter as the bolt or nut is rotated, similar to the way snowball increases in size as it is rolled across more snow. This will effectively lock the threads together and prevent disassembly ever.

The only way to separate the 2 parts after this condition occurs is to destroy one if not both parts. Special coatings can prevent this; exercise caution when assembling like materials if they are stainless or aluminum; the use of an anti-seize compound is highly recommended.

mrbythatmuch · 3 November 2006

When would you not want to use anti-seize? Is there an anti-seize specific to the materials used on the NSX?

Specifically I recently had exhaust work done and asked why anti-seize was not used. I was told the coatings on the bolts was all that was needed and anti-seize could promote corrosion.

Bob Kenney · 3 November 2006

mrbythatmuch said:
When would you not want to use anti-seize? Is there an anti-seize specific to the materials used on the NSX?

Specifically I recently had exhaust work done and asked why anti-seize was not used. I was told the coatings on the bolts was all that was needed and anti-seize could promote corrosion.

Anti-Seize promotes corrosion

The anti-seize used needs to be specific to the purpose; there are many different types of anti-seize compounds but they are all used to PREVENT corrosion not to promote it. I have used these compounds in steel mills, oil platforms and many different engine application. I have never encountered a problem with them; I only had the benefit of being able to disassemble parts that normally become frozen together due the harsh environments they operate in. Is it possible that corrosion may have resulted somewhere to someone using theses products? I suppose so but not to me under any of the conditions I have encountered and we specialized in maintenance machining for a variety of industries.

Hugh · 3 November 2006

ediddynsx said:
Damn! I guess someone got an A in chemistry :wink: :tongue:

Although I did ok in chemistry, this time IJFGI! :biggrin:

silver2002 · 24 November 2012

Has anyone dipped or re-coated bolts to reuse them?
I looked up: DACROTIZED and Dacrodip on Google and found other hits.
I am looking at removing front brake splash guards - technically I should use
8 new bolts [ 96 dollars total] --I'd like a better solution - anything commercially available to coat them?

Hugh said:
Depending on the part being bolted on why not use aluminum fasteners? Zinc would be the next best choice. The Honda "special bolts" are coated in Dacro which is made primarily from zinc and aluminum.

"The Dacrodip solution is a dispersed aqueous solution made from metallic zinc and aluminum flakes, chromic acid and glycol etc. For coating, the duly cleaned components are dipped into it and any excess solution is removed by spinning. Then the components are heated to about 300 deg C in an oven in a closely controlled atmosphere. The hexavalent chromium gets reduced to trivalent chromium i.e. an insoluble amorphous oxide. This acts as a binder for the many overlapping flakes of zinc and aluminum to form a film. At the same time the chromic acid in the solution also reacts with the substrate forming a chemical bond providing a strong adhesion."

steve k · 25 November 2012

I have just picked up a product called Tef Gel,from a marine supply shop in HNL(POP)it is specificly used to stop dissimilar metal corosion,not cheap $32 for 2 ounces but a little goes a long way and thats about the cost or a reasonable case of beer where i live....steve

silver2002 · 25 November 2012

steve k said:
I have just picked up a product called Tef Gel,from a marine supply shop in HNL(POP)it is specificly used to stop dissimilar metal corosion,not cheap $32 for 2 ounces but a little goes a long way and thats about the cost or a reasonable case of beer where i live....steve

Steve: Thanks-- Tef-Gel gives all sorts of hits - even readily available through Google Shopping and Amazon.

I wonder if any NSX bolts are replaced for torque or wear reasons in addition to the need for a fresh coating to prevent galvanic action.

This is from their home site. http://www.tefgel.com

Copy from tef-gel site-

The function of Tef-Gel in eliminating dissimilar metal corrosion is the elimination of electrolytes from entering the interface of the metallic surfaces. Tef-Gel paste contains 40% PTFE powder and 0% volatile solvents, no silicones or petroleum solvents to evaporate, which would leave voids for electrolytes to be drawn into creating a galvanic cell. When both surfaces are coated and mated with Tef-Gel there are no voids for electrolytes (saltwater) to be drawn in by capillary action over extended periods of time.EXAMPLE:A. Bolt with nut or lock nut. Bolt into tapped aluminum, steel, stainless steel, inconel.
Use mascara brush, bottle brush, or toothbrush to apply a thin coat of Tef-Gel to both the threaded hole and the bolt threads and tighten. (Torque requirements may have to be altered according to application of thread lubricants).B. Bedding surfaces: A closely mating surface (10 mils .010 or closer) can be protected from capillary action by applying a thin coat of Tef-Gel with brush, toothbrush, or plastic scraper and assembling the parts and cleaning excess product with mineral spirits or WD-40.Tef-Gel does not electrically insulate hardware. The PTFE (40%) is ultra fine powder that will extrude out of the contact area and into the voids of the surrounding areas.Tef-Gel applied between electrical contacts and connectors does not increase the resistance of the connections even at hundreds of amps, maintaining the integrity of EMI shielding.2. The function of Tef-Gel in eliminating seizing galling and friction welding of stainless steel, inconel, and other nickel alloys.EXAMPLE:Tef-Gel applied to both mating surfaces of nuts and bolts or threaded holes and bolts leaves a layer of 40% solid PTFE within the thread interface, which works as friction barrier. Tef-Gel, which contains 0% volatile solvents, will no evaporate, cold flow, or dry out, giving protection many years later when hardware must be dissembled.Cage Code: 05SA2
NSN: 8030-01-450-4009
HMIS Rating 100BTef-Gel is a registered trademark of Ultra Safety Systems, Inc.

nigel · 25 November 2012

We've been using Tef-Gel for years in the aviation industry to stop bolts and screws seizing and although it's a mess to use a "little does go along way".
It is just about the best anti-seize / corrosion preventative i've used except in high temp situations. Then you should use "C-5 Gold" anti-seize.

There is another barrier in aviation but some don't like it because it's highly toxic. I'll bet they won't even let it in California.
It's called "Mastinox". It is a moisture barrier by design but works like an anti-sieze. It's bright yellow/green and works fantastic but as stated before.

Cheers
nigel

Are special bolts really needed to prevent corrosion to aluminum?

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