Using non-aluminum material on NSX

[ak]

I was wondering, if you are to build a rollbar or roll cage for the NSX, I would doubt that anyone will use Aluminum. So how do you use steel or anything else in NSX without causing any harm? I think that using steel directly on aluminum is a big no no, correct?

-ak

 

[TigerNSX]

I was wondering, if you are to build a rollbar or roll cage for the NSX, I would doubt that anyone will use Aluminum. So how do you use steel or anything else in NSX without causing any harm? I think that using steel directly on aluminum is a big no no, correct?

-ak

That is an interesting point. I wonder if anyone else has a comment on this.

 

[docjohn]

afaik you need only bolt the cage in.The metalurgy involved will not allow welding.

 

[zomby woof]

docjohn is correct, aluminum and steel don't stick together very well.

aluminum is anodic to steel, which means that at the aluminum/steel joint, the aluminum is what will corrode at the highest rate. however, the galvanic reaction is also a function of surface area, so that a relatively small section of steel (roll cage), joined to a relatively large chunk of aluminum (chassis) reduces the rate of corrosion.

another consideration is that our cars are mostly 5000 and 6000 series aluminum, both of which are highly resistant to corrosion.

a further consideration it that roll cages are generally made from low-alloy steel, which resides relatively (there's that word again) close to aluminum on the galvanic chart. their galvanic properties are similar enough to reduce corrosion rate (there's THAT word again, too) yet again.

so, for the lowest corrosion RATE (you're not going to stop it), use a low-alloy steel (for example, 4130) roll cage, primed & painted (especially at the chassis attach points), making sure your car is at least primed in the attach mount holes. a further precaution would be to apply a non-conductive sealant to the bolts and mating surfaces (wet installation) at installation, to reduce moisture intrusion into the joint.

all that said, you're actually increasing your chances of injury if you run a roll cage in your street car, unless you plan to wear a helmet while driving to the grocery store.

 

[ak]

Thanks Dave...that's some good stuff. Do you think people will look at me funny if I wore helmet to a grocery store?

 

[titaniumdave]

There are many places Honda uses steel against aluminum in the NSX, bumper beams, reinforcing beam that connects the front suspension castings and holds the steering rack, front motor mount beam, seat rails, reinforcing tube in the dash, etc. All of these are just painted and use treated bolts. The galvanic corrosion must not be too large an issue, I would follow Honda's lead and paint and use treated nuts and bolt.

I think a bigger issue is differences in strength and rigidity which can cause some very big problems in an accident if loads are not taken into account, and how the loads are transfered between the materials when in a failure mode. Harness bars use designed in reinforcement points from the seats and seat belts, when you add more points of contact, make sure they are capable of taking the load upon impact.

Unless you are going racing, I don't think you are going to find much advantage in bolting a roll cage in an NSX. Many production cars use a 6-10 point roll cage to increase rigidity of the chassis and there is a big return in cornering ability as chassis flex is controlled. The NSX in it's stock version is one of the most rigid chassis ever made for the street.

 

[AU_NSX]

The reason you will not have any corrosion problems bolting a steel roll cage directly to the aluminium chassis...

You need to have both metals sitting in a salt solution to enable the electrons to flow and thus cause galvanic corrosion. With out the salt solution there will be no current and therefore no corrosion.

The NSX I'm buying has had a steel roll cage installed for 10 years... No problems

 

[zomby woof]

au_nsx: galvanism is electric current produced by chemical action, such as in nickel-cadmium batteries. contact (or close proximity, with a suitable transfer medium) between dissimilar metals will initiate the electron flow (electric current) necessary, and, therefore, chemical reaction, with the surrounding environment to stimulate corrosion.

salt water (or salt vapor) will certainly exacerbate corrosion problems, but in everyday use, plain old oxygen (whether atomic or molecular) will provide adequate food for aluminum to react to become aluminum oxide, or steels to convert to ferrous oxides.

the key to corrosion prevention is to block the electron flow between corrodants (anodes) and corrosives (cathodes), which, as titaniumdave suggests, is fairly adequately achieved at the factory by using paint and coated bolts.

the tendency of all things is to return to their lowest energy states, and if there's enough chemistry goin' on for one aluminum atom to shed an electron and pick up an oxygen atom to get a little rest, then he'll do it. it's the electron flow due to galvanism (dissimilar metals) that accelerates and concentrates the process, but salt water isn't the only initiating factor.

 

[AU_NSX]

au_nsx: galvanism is electric current produced by chemical action, such as in nickel-cadmium batteries. contact (or close proximity, with a suitable transfer medium) between dissimilar metals will initiate the electron flow (electric current) necessary, and, therefore, chemical reaction, with the surrounding environment to stimulate corrosion.

salt water (or salt vapor) will certainly exacerbate corrosion problems, but in everyday use, plain old oxygen (whether atomic or molecular) will provide adequate food for aluminum to react to become aluminum oxide, or steels to convert to ferrous oxides.


the key to corrosion prevention is to block the electron flow between corrodants (anodes) and corrosives (cathodes), which, as titaniumdave suggests, is fairly adequately achieved at the factory by using paint and coated bolts.

the tendency of all things is to return to their lowest energy states, and if there's enough chemistry goin' on for one aluminum atom to shed an electron and pick up an oxygen atom to get a little rest, then he'll do it. it's the electron flow due to galvanism (dissimilar metals) that accelerates and concentrates the process, but salt water isn't the only initiating factor.

Zomby woof, You are correct and incorrect at the same time! You are actually talking about two very different chemical reactions.

Oxidation or "rusting" is a chemical reaction that involves a metal combining with an Oxygen atom to form an oxide. Oxidation will happen independent of another metal being present. Salt water and fresh water or even pure water actually slow the oxidation reaction down. Oxidation is actually at its most aggressive when a metal is exposed to air.

Now what we are really talking about is a galvanic reaction, or galvanic corrosion between two metals...

Galvanic corrosion cannot take place without the presence of an electrolyte. Without an electrolyte there can be no electron flow!

The potential for galvanic corrosion is a measure of how dissimilar metals will corrode when placed against each other in an assembly. Metals close to one another on the Galvanic chart generally do not have a strong effect on one another, but the farther apart any two metals are separated, the stronger the corroding effect on the one higher in the list. The presence of an electrolyte (eg. "salt" water, is any water containing dissolved ions) is necessary for galvanic corrosion.

GALVANIC CHART

CORRODED END ( ANODIC OR LEAST NOBLE)
MAGNESIUM
MAGNESIUM ALLOYS
ZINC
ALUMINUM 5052, 3004, 3003, 1100, 6053
CADMIUM
ALUMINUM 2117, 2017, 2024
MILD STEEL (1018), WROUGHT IRON
CAST IRON, LOW ALLOY HIGH STRENGTH STEEL
CHROME IRON (ACTIVE)
STAINLESS STEEL, 430 SERIES (ACTIVE)
302, 303, 304, 321, 347, 410,416, STAINLESS STEEL (ACTIVE)
NI - RESIST
316, 317, STAINLESS STEEL (ACTIVE)
CARPENTER 20 CB-3 STAINLESS (ACTIVE)
ALUMINUM BRONZE (CA 687)
HASTELLOY C (ACTIVE) INCONEL 625 (ACTIVE) TITANIUM (ACTIVE)
LEAD - TIN SOLDERS
LEAD
TIN
INCONEL 600 (ACTIVE)
NICKEL (ACTIVE)
60 NI-15 CR (ACTIVE)
80 NI-20 CR (ACTIVE)
HASTELLOY B (ACTIVE)
BRASSES
COPPER (CA102)
MANGANESE BRONZE (CA 675), TIN BRONZE (CA903, 905)
SILICON BRONZE
NICKEL SILVER
COPPER - NICKEL ALLOY 90-10
COPPER - NICKEL ALLOY 80-20
430 STAINLESS STEEL
NICKEL, ALUMINUM, BRONZE (CA 630, 632)
MONEL 400, K500
SILVER SOLDER
NICKEL (PASSIVE)
60 NI- 15 CR (PASSIVE)
INCONEL 600 (PASSIVE)
80 NI- 20 CR (PASSIVE)
CHROME IRON (PASSIVE)
302, 303, 304, 321, 347, STAINLESS STEEL (PASSIVE)
316, 317, STAINLESS STEEL (PASSIVE)
CARPENTER 20 CB-3 STAINLESS (PASSIVE), INCOLOY 825
NICKEL - MOLYBDEUM - CHROMIUM - IRON ALLOY (PASSIVE)
SILVER
TITANIUM (PASS.) HASTELLOY C & C276 (PASSIVE), INCONEL 625(PASS.)
GRAPHITE
ZIRCONIUM
GOLD
PLATINUM
PROTECTED END (CATHODIC OR MOST NOBLE)

As you can see Aluminium and Steel are next to each other on the chart so there is very little galvanic potential between the two anyway, even if an electrolyte is present.

 

[zomby woof]

as far as being simultaneously correct and incorrect, well, that's what engineering is all about. :biggrin:

as far as your last post, you both confirm what i wrote and dispute what you wrote in your previous post.

i think we're saying the same things, that the best way to preclude corrosion (because you'll never stop it) is to protect the metals under discussion from contact with each other as well with air, so that corrosion is kept to a minimum.

however, there are several types of steels, and Ti and Al, that actually use corrosion as corrosion protection, and which should NOT be painted, which is a whole other topic.

 

[AU_NSX]

as far as being simultaneously correct and incorrect, well, that's what engineering is all about. :biggrin:

as far as your last post, you both confirm what i wrote and dispute what you wrote in your previous post.

i think we're saying the same things, that the best way to preclude corrosion (because you'll never stop it) is to protect the metals under discussion from contact with each other as well with air, so that corrosion is kept to a minimum.

however, there are several types of steels, and Ti and Al, that actually use corrosion as corrosion protection, and which should NOT be painted, which is a whole other topic.

Dave your not quite understanding me... What I am saying is:

1. You don't have to worry about any galvanic corrosion when you bolt a steel roll cage directly onto an aluminium chassis because there will be no electrolyte to facilitate the galvanic corrosion.

Air is not an electrolyte. An electrolyte is a liquid that has free electrons, which are available to flow to facilitate an electric current. A liquid that has these free electrons in it is called a "salt" solution. Fresh water can be an electrolyte if it is not pure, as it will have dissolved minerals in it.

2. To ensure that a metal does not oxidise or "rust" you must not let air come into contact with it, and the paint does an adequate job of that.

So I'm sorry Dave if my posts are not that clear. Even after 7 years at university doing a double bachelor degree in chemistry and then engineering, I still seem to have trouble imparting my knowledge onto others... Good thing I'm not a lecturer eh?! :smile:

 

[LJSB]

Gold NSX I am confused.
If I am reading this right you state that if you that bolt bare mild steel up to bare aluminum, like the series that the NSX, Jaguar, Audi A8 are made of and, there will be no galvanic reaction between the two metals?

The seminars that I have attended by different manufacturers have stated very clearly in their training that mere stray bits of steel in a used file, hammer, sandpaper etc., left behind on a aluminum panel and will cause a galvanic reaction. They have stated concerns over the smallest bit of steel dust landing on the bare aluminum panels. When repairing the mostly Aluminum A8, Audi wants the repair shop to have separate, isolated, dedicated repair bays to help prevent panel contamination and a galavnic reaction.
They are wrong? It won't happen?

The metal cleaners, mastic, caulk, plastic washers, primers and coatings and separate tools ie. hammers, dollies, discs, backing pads, sandpaper,wipes etc., for aluminum only are not mandatory for repairing aluminum cars that exist outside of perfect lab conditions?

Inquiring minds want to know.

 

[AU_NSX]

Gold NSX I am confused.
If I am reading this right you state that if you that bolt bare mild steel up to bare aluminum, like the series that the NSX, Jaguar, Audi A8 are made of and, there will be no galvanic reaction between the two metals?.

Yes, if you that bolt bare mild steel up to bare aluminum, there will be no galvanic reaction between the two metals.

However, if it is in an area where it can get wet or some other substance can complete the circuit then you will get a galvanic reaction

The seminars that I have attended by different manufacturers have stated very clearly in their training that mere stray bits of steel in a used file, hammer, sandpaper etc., left behind on a aluminum panel and will cause a galvanic reaction. They have stated concerns over the smallest bit of steel dust landing on the bare aluminum panels. When repairing the mostly Aluminum A8, Audi wants the repair shop to have separate, isolated, dedicated repair bays to help prevent panel contamination and a galavnic reaction.
They are wrong? It won't happen?

I know nothing about panel repair so what I say now is just an educated guess... If you have steel filings or steel dust in contact with aluminium and then you paint it... It is likely that the paint will act as an electrolyte and you will indeed get a galavnic reaction.

The metal cleaners, mastic, caulk, plastic washers, primers and coatings and separate tools ie. hammers, dollies, discs, backing pads, sandpaper,wipes etc., for aluminum only are not mandatory for repairing aluminum cars that exist outside of perfect lab conditions?

Once again I am not sure about working with Aluminium. I heard that in the development of the NSX that Honda had to use different methods to form and prepare the panels than they used for steel. I suppose because Aluminium has a different modulus of elasticity and more ductile than steel. This may be the reason for the special tools as well.

Inquiring minds want to know.

I am sorry I can not be more help to your specific application. You are constantly providing detailed and expert help to NSXPrime members and are a real asset to the Prime community.

I wish I had more knowledge on cars and car repair, but I am not in the industry. I am a civil engineer and we use this process of galvanic corrosion to protect the steel in bridges, the reinforcing in concrete and extensively in the oil and gas platforms and refineries. In the LNG processing plant I worked on recently we used some very exotic pipe work where different bare metals were fused together (not in an alloy, it was more like plating an inch thick!) in the same pipe such that they formed a pipe within a pipe...

So I don't seem to be able to help too many people here on Prime except to maybe regurgitate the things I have learned from other Prime members like you and nsxtasy, DanO and docjohn etc just to name just a couple. But when I can help I will write what I do know about.

 

[LJSB]

In the LNG processing plant I worked on recently we used some very exotic pipe work where different bare metals were fused together (not in an alloy, it was more like plating an inch thick!) in the same pipe such that they formed a pipe within a pipe...

I envy and respect you for getting to work on projects of that nature. Guys like me get to work on engineer's dreams and without their guiding knowledge we be screwing up or rather, wouldn't know which way to even TURN the screw.
Thanks for the explanations.

 

[AU_NSX]

Thanks for the compliment, and the alternate view... Here I was thinking that I wished I worked on cars or planes or anything else sometimes... :smile:

 

[zomby woof]

ok, well, you have what i've said, so you can take it or not. did you read my personal profile? aircraft structural engineer (bachelor degree), FAA-licensed Airframe & Powerplant Mechanic...i have been an adjunct professor of aircraft maintenance and corrosion control at a local college; twice a year i lecture and tour USAF Weapons School students through our plant to show them what we're doing about corrosion and aircraft maintenance and life extension. at work i train other engineers and production workers in detecting and working corrosion problems. for two years i worked at Avalon Airfield near Geelong, on RAAF P-3 Orions. i have worked on literally every type of airplane in the air today, from J-3 Cubs to SR-71 Blackbirds. every day at work i encounter corrosion. since january, 1975.

pbassjo is exactly correct: Air Force/Navy corrosion control manuals warn not to use steel brushes (especially stainless) to clean aluminum materials, not to use the same abrasive pads on steel and then aluminum, to not even grind steel in close proximity to aluminum materials.

it appears you're missing something from chemistry, and that is that chemical reactions take place one electron, one atom, one molecule at a time. to say that plain old air isn't an electrolyte and therefore doesn't promote corrosion is to discount that air contains about 28% oxygen, and mixed in there is water vapor, and any number of ions and free electrons floating around just dying to make some chemistry. sounds electrolytic.

to say that paint prevents air from contacting the metal it's covering is again oversimplifying the chemistry. the point of paint is to displace moisture, and then to seal out as much more moisture as possible. the trick is to make the paint polymers form a tight enough "net" to keep out more moisture (again, air), and to preclude the trapped moisture from autocatalyzing the substrate. but moisture and air are trapped in any paint applied in anything but a strictly controlled (e.g., a vacuum) environment.

by definition, dissimilar metals in contact will produce a galvanic reaction. that's how batteries work, as i said earlier. by experience, IDENTICAL unprotected metals in spotwelded panels corrode more quickly than single, unprotected panels, because air (and, therefore, moisture) is trapped between the panels. and if i was smart enough to know how to load pics on this infernal contraption, i've got some good ones to show. also, differing aluminum alloys in contact will cause galvanic corrosion.

i have spent half of the past week inside a wing fuel tank, where the predominant vapors are hydrocarbon-based, repairing...corrosion.

there is no way to prevent corrosion. we can only try to minimize it, or delay deleterious effects. in the airplane business, we use lots of steel fasteners to join aluminum parts, and the fasteners are cadmium-plated to further help prevent corrosion. we install these fasteners wet with sealant to help even more. on top of that, we apply sealant to the nuts/collars. then we prime & paint. standard procedure for joining steel to aluminum is cad plate the steel, epoxy prime both, and apply non-conductive, moisture displacing sealant to the mating surfaces and wet join. but when the airplanes come in for overhaul, the first thing we do is strip off the paint and look FIRST at those steel fasteners for...corrosion. galvanic corrosion. under the paint.

but unless you're on the moon, joining bare steel and bare aluminum will set up galvanic cell corrosion.

this is my last volley till i can figure out how to post pics.

 

[tomc92bb000059]

I also have a question. Why is it that aluminum fasteners, when bolted to steel motorcycle frames, always seem to "corrode" inside and on the threads, leaving behind a white chalky residue? And that within 4 years, as evidenced by my 2000 ZX12? And not just at the top of the bolt where it is exposed to the elements, but all the way down to inside the tip of the bolt...Isn't that what we are concerned about here? I may not be using the terminology properly, as I am just a regular CE who hasn't even passed the PE yet..

Some type of reaction does take place, otherwise that white material would not be there.....

 

[docjohn]

Some very useful and helpful info.I think our two chemists/engineers are on the same page,but one is talking in more hypothetical terms or as controlled absolutes,however for all practical purposes our cars need to be designed with water as an everpresent component and is expected in the metalurgy of a car or plane.Good stuff though guys!

 

[AU_NSX]

I also have a question. Why is it that aluminum fasteners, when bolted to steel motorcycle frames, always seem to "corrode" inside and on the threads, leaving behind a white chalky residue? And that within 4 years, as evidenced by my 2000 ZX12? And not just at the top of the bolt where it is exposed to the elements, but all the way down to inside the tip of the bolt...Isn't that what we are concerned about here? I may not be using the terminology properly, as I am just a regular CE who hasn't even passed the PE yet..

Some type of reaction does take place, otherwise that white material would not be there.....

The white chalky residue is Aluminium oxide. It is caused by OXIDATION and has nothing to do with the fact that it is attached to a steel frame.

The chemical equation for the corroding of aluminium in air is:

4Al(solid) + 3O2(gas) = 2Al2O3(solid)

This is OXIDATION there is no galvanic reaction happening here at all.

So you can see that oxidation is indeed a chemical reaction, as is a galvanic reaction. However, from the above equation you can see that the steel (Fe) plays no part in the oxidation of aluminium, and will oxidise whether it is attached to a steel frame or not. Quite simply the aluminium is bare and exposed to the atmosphere and therefore it is oxidising. The white chalky residue is what Aluminium looks like when it "rusts"

 

[AU_NSX]

Some very useful and helpful info.I think our two chemists/engineers are on the same page,but one is talking in more hypothetical terms or as controlled absolutes,however for all practical purposes our cars need to be designed with water as an everpresent component and is expected in the metalurgy of a car or plane.Good stuff though guys!

Exactly Doc!

I don't have any problems with my (steel) roll cage being bolted to the Aluminium chassis for over 10 years now, and I was trying to explain in theory why I am not having any galvanic corrosion or oxidation corrosion issues.

Dave obviously knows his stuff and it would be great to meet him and discuss the work he does, as it sounds very interesting to me. I know the chemistry and theory behind the stuff I am working on, but he gets to put it into practice on some of the most advanced machinery we have on the planet!... interesting stuff!

Sometimes in this medium of communication you can be misunderstood though and taken the wrong way. :smile:

 

[John McCain Racing]

Thanks Dave...that's some good stuff. Do you think people will look at me funny if I wore helmet to a grocery store?

I've always wanted to do that just to see peoples reaction! Let me know how it goes. Wear the helmet inside Giant too. You might end up in the nut house!

 

[docjohn]

I'm amazed at how many companies now offer cosmetic only bolt-in "cages" for the street compact market.The idea I guess is to bring the race style to the street scene,but are they even street legal,and are they flimsy enough that they would'nt split your skull open if you were in an accident?

 

[John McCain Racing]

I'm amazed at how many companies now offer cosmetic only bolt-in "cages" for the street compact market.The idea I guess is to bring the race style to the street scene,but are they even street legal,and are they so flimsy that the would'nt split your skull open if you were in an accident?

The roll bar that Comptech offers for the NSX kinda falls in line with that. It really doesn't help with a "roll over" and isn't SCCA legal either. I think a grand is a bit much for pretty much nothing besides the fact you can say you have a roll bar!

 

[tomc92bb000059]

The white chalky residue is Aluminium oxide. It is caused by OXIDATION and has nothing to do with the fact that it is attached to a steel frame.

The chemical equation for the corroding of aluminium in air is:

4Al(solid) + 3O2(gas) = 2Al2O3(solid)

This is OXIDATION there is no galvanic reaction happening here at all.

So you can see that oxidation is indeed a chemical reaction, as is a galvanic reaction. However, from the above equation you can see that the steel (Fe) plays no part in the oxidation of aluminium, and will oxidise whether it is attached to a steel frame or not. Quite simply the aluminium is bare and exposed to the atmosphere and therefore it is oxidising. The white chalky residue is what Aluminium looks like when it "rusts"

Cool. So is there a way to prevent it, is it destructive, and are there any parts on the NSX that we need to be concerned with?

 

[zomby woof]

our cars will corrode in the same places as steel cars: in the trunk, lower parts of body panels, battery tray, around the windscreen...essentially any place moisture can accumulate, including areas where there are rubber seals (rooftop, window trim, et c). however, since honda uses the more corrosion-resistant aluminum alloys, and anodizes the metal before paint, corrosion will probably take longer to show up than in steel cars. when it does appear (as it already is on my car, but that's because previous owners weren't very appreciative of the car), it will show up as discolored/blemished paint areas on body panels, blistered/peeling paint around fasteners, or, in more advanced stages, white powder (aluminum oxide). sometimes the blistering/peeling paint around fasteners is difficult to distinguish from results of normal maintenace, but if the fasteners are rusty, it's a good idea to replace them, preferably with good honda factory-coated fasteners.

where i have found corrosion so far, and it's really not much, is around the fastener holes that attach the taillight lens boxes, in the trunk well where the (alleged, because i've never actually seen one :tongue: ) tool kit resides, and the battery/spare tire tray.

i also have three blemished spots on my driver's side B-pillar cover panel, indicating there is probably corrosion behind there. i can't wax out the blemishes, which tells me it's coming from the back side.

wash any spilled battery acid from your battery tray with clean water, and it should survive just fine. don't clean bare aluminum with alkaline solutions, unless you're prepping for paint, and DON'T paint over corrosion. aluminum protects itself by forming an aluminum oxide layer, but in a continually damp area, or if the corroded material is painted over, the corrosion becomes autocatalytic and won't stop growing.

our suspension bits look real pretty when they're polished, but that's a quick way to induce corrosion, because you're removing the self-protective aluminum oxide layer. that dull finish may not be attractive at a car show, but its function is what's important...remember, "pretty is as pretty does."

http://www.engineersedge.com/corrosion.shtml