Corrosion protection for long life

[John F. Russo]

Wow!

My company phone system went down and I come back in a couple of days to converse on the thread, "Metco Control Arms NOW available in Black Powdercoat !!!", that I re-opened on a legitimate issue, and it felt like I fell from the sky into the gun battle at the OK corral. (I rather enjoyed that battle.) Of course, I'm exaggerating. But I didn't feel that the discussion was off target, even though there were a couple of snide remarks. We don't have to be that sensitive do we?

In any case I have had concerns about the corrosion issue in the aluminum front cross bar and the engine cradle.

I made the following statement on 9/27/03 in the thread called, "Alum Front Susp, any known problems??"

"I worked on an R & D contract on stress corrosion of high strength aluminum alloys in the late 60's. I was an assistant to two doctoral degreed project leaders- one in metallurgy (Fulbright Scholar, not related to president Clinton) and one in electrochemistry. The basic principle is that corrosion is accelerated when the part is stressed in the presence of road or sea salt, in the case of my work that was related to airplanes.

As soon as I found out that the MM's control arm was made of an aluminum alloy, I became concerned. I live in a salt environment during the winter and have had the car since early March and have had minimal salt exposure so far." (I don't know why the some of the above words are in red. I don't have the time to figure out how to change them either.)."

Today I just read TripleTransAm's comment in the above "Metco Control arms..."closed" thread, "The reason your comment alarms me is because I highly doubt my 1985 Parisienne's control arms were aluminum, and one side rusted through in 1998 after some 110 000 miles of all-weather driving. Granted, the car was garaged pretty much every winter, which I'm sure did not help the corrosion resistance, but still...
So if steel is supposed to outlast aluminum, what's in store for my Marauder, come a few years from now?"

Now I find my concern justified because the last car that I am going to own in the remaining years of my life...who knows 5, 10 or more years...is my MM! I drive about 18,000 miles /year year-around. My car is not even garaged.

I would like to now open the discussion up again. So let's keep everything below the Logan's supersensitive radar. (Have you patented yet? P.S. That's a joke. Remember I did contribute $50 toward this site. Maybe it's time for another contribution. But those pop-up screens...)

I'm considering some protective coating for the underbody like a Rusty Jones or other especially for the aluminum parts. So let's have some civil feedback.

I still feel the the powder coating on the aluminum control arms will provide me good protection against the salt. Are they available in steel as SergntMac said?

Other comments from the Metco Control arms thread
SergntMac
"John [John F. Russo], you're a bad boy now, shame on you. You must have known better, your education says so. Why have you asked all this scientific stuff in these channels, when you know many of us don't get that?"

My response
I don't have a personality analysis chart on who is sensitive to what. I just asked a reasonable question.

TAF
"There are no black Metco Control arms available anymore. Only 2 cars will have these, Marty's and one other lucky person who ordered black. Everyone else wanted the clear annodized."

My response
I called Aaron today and he told me that I could have the control arms black powdered coat at an additional cost of $42 for all four arms.

[MERCMAN]

John, contact Silver 04, he is an engineer and he and i discussed the benefits of powdercoating on steel and aluminum. I think he will be able to answer your questions. :up:

[Dr Caleb]

A fair question John. I had wondered the same thing, but was far too late to ask it in that thread.

Remembering basic chemistry, it seems to me that low phosphorus stainless steel contians no metals that oxidize in the presence of salt and/or water. I can verify that the stainless steel exhaust that came stock with my Crown Vic is intact and perfect after seeing 12 Alberta winters. The only problem with the exhaust has been the H pipe, which rusted out because it is not made of stainless steel. I had to replace the oilpan this year, because it was nearly rusted through, but the exhaust is perfect.

Aluminum oxidizes on contact with air. I don't know much about the effects that stress will play in this, but to me, it's obvious that things made of aluminum will suffer this fate if allowed to remain in contact with wet, salty water. Therefore clearcoating or powdercoating these aluminum components should be an issue, or at least a consideration, for anyone who will drive their marauder in a wet, salty environment.

:twocents:

[ahess77]

Having designed aluminum, zinc, magnesium, and plastic automotive parts, here's my opinion of what I’ve seen through analysis of high-life parts (that is 7+ years in the field and 80k+ miles).

Aluminum (I’m discussing common aluminum alloys used in automotive) does react with the environment and with interfacing parts (galvanic reactions with some fasteners can cause very high back-out torque, on smaller fasteners usually to the point of failure.) However, 10 years in the field or 1000 hours salt spray testing later, I have not seen that aluminum parts have structural decay. Yes, the textbooks say you’ll get microfractures caused by corrosion reactions that can expand across grain boundaries and propagate into catastrophic failures. I have seen this in the lab on all types of metals. But usually because of poor part design that had high stresses where they should not have been.

Aluminum does “rust” when exposed to normal exterior conditions with salt and water and other agents found in every day driving. You will usually see a white corrosion form on the part. However, the breakdown of the part, compared to steel, it is so slow that I have not seen part component degradation in the high mile teardowns due to the white “rust”. The white corrosion is usually objectionable to customers so typically a 240 hr phosphate or dichromate coating is used to prevent the white flaky stuff from forming during the warranty period. Aluminum parts are also typically over designed by engineers who are used to making steel parts and therefore overcompensate to prevent failures when designing for aluminum.

What I would be concerned about when looking at aluminum suspension parts is anywhere there is an interface to a part that has some give or slip, i.e. a hole for a rubber bushing because: 1. Aluminum is so soft that if a bushing is slipping in a hole it can wear away the aluminum. I have seen plastic parts completely smooth down features on aluminum brackets over 7 to 10 years of usage. and 2. The white corrosion that can form may push the bushing out-of-place.

An e-coat or powder coat on aluminum will last a LONG time, if nothing is rubbing or chipping it away. Paint will last as long on aluminum as it does on steel. In my opinion an aluminum part bolted down on both ends doesn’t really need protection from the elements since the steel fasteners will likely degrade faster than the aluminum. The only reason to coat it would be for appearance issues, not structural.

Now, having said all that, here’s my engineering opinion. If you want to be concerned about keeping your Marauder for a long time without parking it in a climate controlled garage, you’ll want to buy a new set of doors. The hem flange on the bottom of the doors will start rusting in about 5 years and in about 10 years the bottom of the doors will be gone. The second thing you should do is to put underbody coating on every single faster head you can see, or replace them with stainless. Fastener corrosion coatings will make it 3 to 5 years, then they’ll be rusting. Again, just my opinion on higher priority corrosion issues our Marauders.

[martyo]

Geez, talk about beating a dead horse.

If this is the last car you are ever going to buy before you go to the big race track in the sky, just buy the damn things! They are under 400 bucks for the set. Surely as a successful businessman you can swing that without missing a mortgageg payment.

If in 5 years they are beat from the road salt (which I highly doubt they will be) and you are still driving (warped rotors and all), you can replace them. And, I will bet by then you will have socked away another 400 clams to buy another set. Heck, I bet if you put a small part of your Social Security check into a cookie jar each week, you might even have change after (if) you ever buy replacements.

[RF Overlord]

I'm considering some protective coating for the underbody like a Rusty Jones or other especially for the aluminum parts. So let's have some civil feedback.

John:

I'm not a big fan of "Rusty Jones"-type undercoating. It's not so much that the undercoating isn't good, it IS good IF, and that's a huge IF, it's installed correctly. The problem with the Rusty Jones (et. al.) franchises is that they were set up just like Jiffy-Lube: get 'em in, get 'em out. Also, the training of their installers was woefully inadequate. The end result was that they did terrible work, and by the time customers had problems, the franchises were out of business, so collecting on the "lifetime warranty" was a joke.

If you're concerned about the longevity of the underpinnings of your MM through the winter months, I suggest going through a "touch free" car wash periodically and getting the "undercarriage spray" or whatever they call it. Nevermind the fact that the car wash does a crappy job removing dirt from the finish, or that it leaves spots on all the windows; at least it will get the salt off the underside...we have similar issues down here on the Cape, and my MM has been through 2 winters now, with nothing abnormal happening to any of the underpieces.

[Dr Caleb]

Marty, get your hackles down bud! We aren't talking anything specific here!

Many parts (control arms, drive shaft, wheels) are alloy aluminum on the Marauder. Many parts are painted steel or like the exhaust, stainless steel.

I've never owned a car with so much aluminum in it, and I for one was wondering what cause and effect winter weather would have on those parts.

ahess77 has given us a really good explanation as to what to expect over the lifetime of the car.

I had my car rust proofed when I bought it, including the doors and all underside exposed frame bolts. Not like I winter drive it, but it's nice to know that i could if I wanted to.

[martyo]

Marty, get your hackles down bud! We aren't talking anything specific here!

Hey with Mac out on detention, someone has to go off on inexplicable tirades. It might as well be me.

[Silver_04]

I wrote a friggin paper. If anyone wants to read it, click HERE (http://www.home.earthlink.net/~ctt9/images/Marauder_dyno/ALorSteel.doc). It's a word file.

Chris

[423REED]

Wow!

My company phone system went down and I come back in a couple of days to converse on the thread, "Metco Control Arms NOW available in Black Powdercoat !!!", that I re-opened on a legitimate issue, and it felt like I fell from the sky into the gun battle at the OK corral. (I rather enjoyed that battle.) Of course, I'm exaggerating. But I didn't feel that the discussion was off target, even though there were a couple of snide remarks. We don't have to be that sensitive do we?

In any case I have had concerns about the corrosion issue in the aluminum front cross bar and the engine cradle.

I made the following statement on 9/27/03 in the thread called, "Alum Front Susp, any known problems??"

"I worked on an R & D contract on stress corrosion of high strength aluminum alloys in the late 60's. I was an assistant to two doctoral degreed project leaders- one in metallurgy (Fulbright Scholar, not related to president Clinton) and one in electrochemistry. The basic principle is that corrosion is accelerated when the part is stressed in the presence of road or sea salt, in the case of my work that was related to airplanes.

As soon as I found out that the MM's control arm was made of an aluminum alloy, I became concerned. I live in a salt environment during the winter and have had the car since early March and have had minimal salt exposure so far." (I don't know why the some of the above words are in red. I don't have the time to figure out how to change them either.)."

Today I just read TripleTransAm's comment in the above "Metco Control arms..."closed" thread, "The reason your comment alarms me is because I highly doubt my 1985 Parisienne's control arms were aluminum, and one side rusted through in 1998 after some 110 000 miles of all-weather driving. Granted, the car was garaged pretty much every winter, which I'm sure did not help the corrosion resistance, but still...
So if steel is supposed to outlast aluminum, what's in store for my Marauder, come a few years from now?"

Now I find my concern justified because the last car that I am going to own in the remaining years of my life...who knows 5, 10 or more years...is my MM! I drive about 18,000 miles /year year-around. My car is not even garaged.

I would like to now open the discussion up again. So let's keep everything below the Logan's supersensitive radar. (Have you patented yet? P.S. That's a joke. Remember I did contribute $50 toward this site. Maybe it's time for another contribution. But those pop-up screens...)

I'm considering some protective coating for the underbody like a Rusty Jones or other especially for the aluminum parts. So let's have some civil feedback.

I still feel the the powder coating on the aluminum control arms will provide me good protection against the salt. Are they available in steel as SergntMac said?

Other comments from the Metco Control arms thread
SergntMac
"John [John F. Russo], you're a bad boy now, shame on you. You must have known better, your education says so. Why have you asked all this scientific stuff in these channels, when you know many of us don't get that?"

My response
I don't have a personality analysis chart on who is sensitive to what. I just asked a reasonable question.

TAF
"There are no black Metco Control arms available anymore. Only 2 cars will have these, Marty's and one other lucky person who ordered black. Everyone else wanted the clear annodized."

My response
I called Aaron today and he told me that I could have the control arms black powdered coat at an additional cost of $42 for all four arms.
There are three elements which, when occurring simutaneously, can cause stress corrosion cracking, namely:

* The presence of tensile stresses which may be the result of bending or welding in a work shop, induced stresses, and high operational stresses.

* High operational temperatures which are typically in excess of 140°F(60°C).

* Aqueous chloride environments.

Failure by cracking results from the selective directional attack that is caused by simultaneous interaction of the sustained tensile stress with the chemical or electro-chemical effects of the service environment of the exposed aluminum surface. Heat treated metals are generally more susceptible to this type of corrosion unless a specific precipitation treatment is carried out (EX: -T7 type tempers). One would assume that the aluminum parts are anodized for surface protection. If not, we'll find out over time.

But, I don't think you need to worry about this issue. You would have to have a combined engineering and metallurgical discusion with the chassis engineer(s) who designed the frame. There is a history of the successful automotive use of heat treated aluminum alloys in chassis parts, including the Audi A8, which is all aluminum!
____________________________
2004 MARAUDER - DTR
1994 TAURUS SHO - DK GREEN

[Warpath]

...Aluminum (I’m discussing common aluminum alloys used in automotive) does react with the environment and with interfacing parts (galvanic reactions with some fasteners can cause very high back-out torque, on smaller fasteners usually to the point of failure.) However, 10 years in the field or 1000 hours salt spray testing later, I have not seen that aluminum parts have structural decay. Yes, the textbooks say you’ll get microfractures caused by corrosion reactions that can expand across grain boundaries and propagate into catastrophic failures. I have seen this in the lab on all types of metals. But usually because of poor part design that had high stresses where they should not have been....


...Failure by cracking results from the selective directional attack that is caused by simultaneous interaction of the sustained tensile stress with the chemical or electro-chemical effects of the service environment of the exposed aluminum surface. Heat treated metals are generally more susceptible to this type of corrosion unless a specific precipitation treatment is carried out (EX: -T7 type tempers). One would assume that the aluminum parts are anodized for surface protection. If not, we'll find out over time.....

I spoke to our resident aluminum expert here at work (automotive OEM). He stated that with the aluminum grades typically used in automotive applications, stress corrosion cracking is not an issue. Automotive typically uses A356 T6, 6061 T6, or 6082 T6 from my experience. Stress corrosion cracking becomes a concern once a particular element in the Al alloy gets above a certain level. I don't remember the element, maybe copper, and he didn't tell me the level. The above aluminum grades do not contain level of this element high enough to promote stress corrosion cracking. Someone mentioned aeronautical/space applications where stress corrosion cracking is a concern. Aeronautical/space applications must use alloys with this element exceeding the limit.


...What I would be concerned about when looking at aluminum suspension parts is anywhere there is an interface to a part that has some give or slip, i.e. a hole for a rubber bushing because: 1. Aluminum is so soft that if a bushing is slipping in a hole it can wear away the aluminum. I have seen plastic parts completely smooth down features on aluminum brackets over 7 to 10 years of usage. and 2. The white corrosion that can form may push the bushing out-of-place...

As you should know, if the part is properly designed and tested, this slipping is not an issue. However, with the suspension components, in the very unlikely even something does slip, it would create a rattle or knock before coming apart and alert the driver something is wrong. Also, dissimilar metals usually have some protective barrier between them such as the finish/plating/coating. So, galvanic corrosion is not an issue during the useful life of the vehicle.


...The only reason to coat it would be for appearance issues, not structural....

I agree completely.


....The second thing you should do is to put underbody coating on every single faster head you can see, or replace them with stainless....

I suggest not switching to stainless steel fasteners unless you have the test facilities and knowledge to know what torque spec to use. Loose fasteners can break and create real havoc. I think it is much more likely you would create a new problem by replacing them with stainless than actually fixing a problem that isn't much of a concern in the first place. I suggest just painting them while on the vehicle if it is a concern.


...If this is the last car you are ever going to buy before you go to the big race track in the sky, just buy the damn things! They are under 400 bucks for the set...

What we are trying to say is don't bother wasting $400 bucks. These concerns are unwarranted. Instead, put the money towards a blower. If $400 is no big deal to you, send $400 my way. I'll find a use for it. :)

[MENINBLK]

I wish you guys were around when FORD RECALLED the Contour because of the Front Springs breaking.

Talk about STRESS FAILURES due to CORROSION...
I had both front springs break, mid coil, because the salt had settled into a crack
in the spring, and it ate right through the coil. :mad2:

Thank GOD there was a recall.

[John F. Russo]

As usual there are good responses to my question.

Because they are so varied, I have to review them over the weekend so that I can attempt to make preliminary conclusions, if possible, before I offer you my plan of action.

Thank you all for the corrosion data, metallurgical insights and practical considerations.

[BillyGman]

hmm, it's a time consuming task to try and sift through all of this thread, but then again, who am I to accuse people of olengthy posts since i do have my share of them. But the bottom line as far as I can see is that aluminum is softer yes, but to my knowledge steel corosion is much more common. So it apears to be a tade-off as far as the materials go(aluminum vs. steel). But aside from the type of metals used, the design comparisant itself between the Metco and other control arms I believe is another story, but since I haven't purchased any of these control arms myself, I'll leave that part of my opinion out. Draw your own conclusions.

[jakdad]

So what all this says is that Marauders are like any other car. Leav'em out there long enough and they will rot to the ground. That's why they make new cars that will rot to the ground. That's life.........................

:hide: :hide: :hide:

[Warpath]

I wish you guys were around when FORD RECALLED the Contour because of the Front Springs breaking.

Talk about STRESS FAILURES due to CORROSION...
I had both front springs break, mid coil, because the salt had settled into a crack
in the spring, and it ate right through the coil. :mad2:

Thank GOD there was a recall.

Springs are not made of aluminum. They're steel. Steel needs to be coated if you don't want it to rust through. The coatings on springs needs to be really good if you want the springs to last. Steel is also susceptable to stress corrosion cracking if it is hard enough. That's why we don't use any fasteners with a property class of 12.9. They are too hard. The property class is the number formed on the head of the bolt. It will be something like 8.8, 9.8, 10.9, etc. I don't know what the numbers mean. But, the higher, the harder the steel.

[Captain Steve]

From: http://www.autoaluminum.org/index.htm

Nature has provided aluminum with a highly protective “skin” in the form of a clear barrier oxide on its surface that forms quickly and is tough enough to hinder the deeper intrusion of oxygen and other gases and liquids to the subsurface aluminum atoms. This oxide is tightly chemically bound to the underlying surface, and if damaged, reforms immediately in most environments. On a freshly abraded surface, the barrier oxide film is only 1 nm (10 angstroms) thick, but is highly effective in protecting the aluminum from corrosion. The oxide film develops slowly in normal atmospheres to greater thicknesses, and when corrosive environments are present, the oxide may both thicken and darken. However, it generally retains its protective character.

Thus, in normal environmental exposure, aluminum does not corrode (rust) away as does steel.


Aluminum surfaces do oxidize when exposed to air, but this differs from the oxidation of steel in two important ways: Aluminum oxide is effectively transparent and invisible to the unaided eye. Aluminum oxide clings tightly to the surface of aluminum and forms a protective film that blocks progressive deterioration.



It does not flake off, thereby exposing fresh surfaces to further oxidation. When damaged, it quickly reforms again, providing continuing protection. With this natural corrosion resistance, the aluminum bodies of many commercial motor vehicles, rail cars and aircraft are unpainted; aluminum has proven durability in such applications.

[merc406]

For us guy's in the rust belt it is best to do all you can to protect the alum. parts. Either paint them or undercoat them, if you drive it in the winter elements.

It's funny no one remembers all the GM cars of the 70's and eighties and other makes I'm sure, with the bumper's missing. And then their were the Ford pick-ups with the alum. frt. reinf. apron strut's. I can go on, but is safe to say that aluim. hasn't changed it's properties and still does the same thing.

[Warpath]

For us guy's in the rust belt it is best to do all you can to protect the alum. parts. Either paint them or undercoat them, if you drive it in the winter elements.

It's funny no one remembers all the GM cars of the 70's and eighties and other makes I'm sure, with the bumper's missing. And then their were the Ford pick-ups with the alum. frt. reinf. apron strut's. I can go on, but is safe to say that aluim. hasn't changed it's properties and still does the same thing.

I disagree. The aluminum parts on vehicles are tested for all known conditions. There is no need to undercoat them regardless of where you live in North America. If you don't like aluminum, you better buy a car now. With CAFE requirements ever increasing, vehicle weight must be reduced. Aluminum is an easy option and you will see more and more of it. Although, on the other hand, it is more expensive and with cost pressures, you may actually see it being replaced with steel.

As for those GM cars and Ford trucks, without knowing the cause of the problem, you can't blame corrosion. Ford had a problem with bumpers falling of F-series in the 90s because of hydrogen embrittlement of the bumper bolts. It had nothing to do with corrosion.

[merc406]

As for those GM cars and Ford trucks, without knowing the cause of the problem, you can't blame corrosion. Ford had a problem with bumpers falling of F-series in the 90s because of hydrogen embrittlement of the bumper bolts. It had nothing to do with corrosion.




You can only put the blinders on for so long -path, having worked on 'em through till the 90's, the problem WAS CORROSION at the point of attachment even with the corrosion pads installed.

[SergntMac]

You can only put the blinders on for so long -path, having worked on 'em through till the 90's, the problem WAS CORROSION at the point of attachment even with the corrosion pads installed.
Well, I'm back after a week's suspension from the site, and I am pleased that y'all pursued the truth. My previous post was a thumbnail sketch of the collective thoughts I read here, and it looks like y'all flushed out the detail you needed, and at a level beyone my personal experience.

What I said back then is reflected here, and many times over. Metals of almost any content will be affected by external forces, it's simply a matter of time, and accelerating conditions.

As I was writing that post, I was remembering my 1977 Dodge Diplomat, in 1980. One day while adjusting the antenna on the right front fender, it all fell through and I had a hole the size of my fist in the top of the fender. Ditto the left fron the next week while washing the car, it's just caved in.

Paint and undercoating helped it all last longer, but's all I was left with, paint and undercoating, the fenders between tem were gone. Hence, I believe all metals have their life span, it's just a matter of time, and various external threats.

Now...What about automotive rubber? Door seals, bushings, body mounts? Poly-something, or genuine rubber?

[jakdad]

Well, I'm back after a week's suspension from the site, and I am pleased that y'all pursued the truth. My previous post was a thumbnail sketch of the collective thoughts I read here, and it looks like y'all flushed out the detail you needed, and at a level beyone my personal experience.

What I said back then is reflected here, and many times over. Metals of almost any content will be affected by external forces, it's simply a matter of time, and accelerating conditions.

As I was writing that post, I was remembering my 1977 Dodge Diplomat, in 1980. One day while adjusting the antenna on the right front fender, it all fell through and I had a hole the size of my fist in the top of the fender. Ditto the left fron the next week while washing the car, it's just caved in.

Paint and undercoating helped it all last longer, but's all I was left with, paint and undercoating, the fenders between tem were gone. Hence, I believe all metals have their life span, it's just a matter of time, and various external threats.

Now...What about automotive rubber? Door seals, bushings, body mounts? Poly-something, or genuine rubber?
I have always believed that undercoating applied without weep holes will actually create rust conditions. I have seen it happen many times over the years. Oops, I may be dating myself having seen that many cars rust out.
:D

[jgc61sr2002]

Sarge - Welcome back. :welcome:

[Warpath]

You can only put the blinders on for so long -path, having worked on 'em through till the 90's, the problem WAS CORROSION at the point of attachment even with the corrosion pads installed.

No blinders - I work on this kind of stuff day in and day out now. So, I have first hand experience too. We don't cover the aluminum grades we use because it is simply not necessary. There are special circumstances where contacting metals are too far apart on the galvanic scale that you need to coat one or the other (such as Al and steel). I am not familar with the failures you mentioned. It could have been GM or Ford did not put a barrier between the Al and steel bumpers which would have led to galvanic corrosion. If that is true, it is not fair to state all aluminum will corrode and fall apart. It only needs to be used properly.