Full Version: intergranular oxidation when you remove anodizing?
Any one ever hear of this? Someone on another suite said that if I were to remove the anodizing from a part it would suffer from this and eventually break. BS or not? TED?
I have to say BS I dont leave it in the solution long enough to do damage it I have been told that anno can structurally make it stronger which I dont believe either it is a color coating not a metal
nonsence!!!! it is true that your bike could rust from the inside out!!!! MYTHE BUSTERS!!!!next episode
Anno is not a coating. It is a hardening of the surface.
In return, removing it does weaken the structure of the aluminium. Additionally it opens the pores to corrosion further weakening the item.
So when you polish an item after removing ano, you should polish with a mix of 1/3 petrolium vaseline mixed with 2/3 polishing compuond. This will seal the pores a bit and also has the benifit of less polishing in the future, just wipe and go. (old harley guy taught me that trick)
quote:Aluminium Anodizers Council
It is an electrochemical process that thickens and toughens the naturally occurring protective oxide. The resulting finish, depending on the process, is the second hardest substance known to man, second only to the diamond. The anodic coating is part of the metal, but has a porous structure which allows secondary infusions, (i.e. organic and inorganic coloring, lubricity aids, etc.)
In return, removing it does weaken the structure of the aluminium. Additionally it opens the pores to corrosion further weakening the item.
So when you polish an item after removing ano, you should polish with a mix of 1/3 petrolium vaseline mixed with 2/3 polishing compuond. This will seal the pores a bit and also has the benifit of less polishing in the future, just wipe and go. (old harley guy taught me that trick)
Intergranular corrosion starts from the inside out, and is very specific as to what types of aluminum can even suffer from it.
Annodizing is a layer of controlled corrosion, or aluminum oxide. Aluuminum oxide is basically ceramic, very hard substance. Suphuric acid and electrictity create the layer. It does not add strength to the metal, but does harden the surface layer. The color is merely dye.
So removing the annodizing exposes the aluminum to corrosion.
If you polish it, and maintiain it, it will not suffer from corrosion.
However a tuff-neck that has sat outside in the rain, and has corrosion in the quill, and has been ridden hard, and flexed, may already have corrosion, and exfoliation corrosion in the quill area. I have seen a few like that, and the annodizing had not been removed.
If you remove the annodizing, and then you leave it un-maintained, and use it in the elements of sun, rain, and dirt, and water, it will not last as long. Thats why they get anodized. Corrosion resistance.
If its being maintained and polished , and is a show piece, then it really doesnt matter.
Corrosion takes place on annodized parts that are scratched, flexed, or damaged as well.
Intergranular corrosion is very specific to copper content within alumunum. Most bike parts aren't made with high copper alloys, in fact I doubt any are made from aluminum like 7075 where intergrannular is common.
Wikipedia....
Aluminium based alloys may be sensitive to intergranular corrosion if there are layers of materials acting as anodes between the aluminium-rich crystals. High strength aluminium alloys, especially when extruded or otherwise subjected to high degree of working, can undergo exfoliation corrosion, where the corrosion products build up between the flat, elongated grains and separate them, resulting in lifting or leafing effect and often propagating from edges of the material through its entire structure. [2] Intergranular corrosion is a concern especially for alloys with high content of copper
I doubt you will ever see true intergranular corrosion on a bicycle part in your lifetime. High copper alloy parts under high loads, can corrode and "Inflate" from the inside, like a pregnant toad, called "Pillowing". Inside the part has become nothing but white powder, and it will crumble easily.
Not to worry.
It will get dull and oxidize if bare aluminum is not maintainted or polished. If you leave it out in the rain and weather, it will fail sooner than if left anodized. But the anodized one will not be far behind it.
[ February 24, 2007, 02:28 PM: Message edited by: Ted Carl ]
Annodizing is a layer of controlled corrosion, or aluminum oxide. Aluuminum oxide is basically ceramic, very hard substance. Suphuric acid and electrictity create the layer. It does not add strength to the metal, but does harden the surface layer. The color is merely dye.
So removing the annodizing exposes the aluminum to corrosion.
If you polish it, and maintiain it, it will not suffer from corrosion.
However a tuff-neck that has sat outside in the rain, and has corrosion in the quill, and has been ridden hard, and flexed, may already have corrosion, and exfoliation corrosion in the quill area. I have seen a few like that, and the annodizing had not been removed.
If you remove the annodizing, and then you leave it un-maintained, and use it in the elements of sun, rain, and dirt, and water, it will not last as long. Thats why they get anodized. Corrosion resistance.
If its being maintained and polished , and is a show piece, then it really doesnt matter.
Corrosion takes place on annodized parts that are scratched, flexed, or damaged as well.
Intergranular corrosion is very specific to copper content within alumunum. Most bike parts aren't made with high copper alloys, in fact I doubt any are made from aluminum like 7075 where intergrannular is common.
Wikipedia....
Aluminium based alloys may be sensitive to intergranular corrosion if there are layers of materials acting as anodes between the aluminium-rich crystals. High strength aluminium alloys, especially when extruded or otherwise subjected to high degree of working, can undergo exfoliation corrosion, where the corrosion products build up between the flat, elongated grains and separate them, resulting in lifting or leafing effect and often propagating from edges of the material through its entire structure. [2] Intergranular corrosion is a concern especially for alloys with high content of copper
I doubt you will ever see true intergranular corrosion on a bicycle part in your lifetime. High copper alloy parts under high loads, can corrode and "Inflate" from the inside, like a pregnant toad, called "Pillowing". Inside the part has become nothing but white powder, and it will crumble easily.
Not to worry.
It will get dull and oxidize if bare aluminum is not maintainted or polished. If you leave it out in the rain and weather, it will fail sooner than if left anodized. But the anodized one will not be far behind it.
[ February 24, 2007, 02:28 PM: Message edited by: Ted Carl ]
He means that you will most often see intergranular and its advanced form, exfoliation, on high load bearing aluminium alloy parts.
And I will debate that people will see it in their lifetime. I have gone to sea aboard the carrier and come back 6mo later only to do a very indepth inspection and find exfo and intergranular in non-loaded zones of Ch-46, F-14, EA-6B, and F/A-18s that were looked at shortly before leaving for deployment. Yes the salt water environment of the ocean does provide a higher content of the electrolyte part of the sorrosion equasion, but many of the folks on this board live within miles or even less of the ocean. therefor it is very reasonable to believe they would see intergranular on an aluminium part in their time.
[ February 24, 2007, 02:43 PM: Message edited by: DMG ]
And I will debate that people will see it in their lifetime. I have gone to sea aboard the carrier and come back 6mo later only to do a very indepth inspection and find exfo and intergranular in non-loaded zones of Ch-46, F-14, EA-6B, and F/A-18s that were looked at shortly before leaving for deployment. Yes the salt water environment of the ocean does provide a higher content of the electrolyte part of the sorrosion equasion, but many of the folks on this board live within miles or even less of the ocean. therefor it is very reasonable to believe they would see intergranular on an aluminium part in their time.
[ February 24, 2007, 02:43 PM: Message edited by: DMG ]
The only area of a bicycle that I have ever even seen exfoliation on, is on a Tuf-Neck stem. But the picture of exfoliation is exactly what you can find in that highly stressed area of a Tuf-neck. But that still is not intergranular.
The area where the quill is pressed into the aluminum is subject to high loads when people were jumpers and hard riders. However, that is still exfoliation. If you sand the areas, you will find layer after layer of thin flakes that will come off.
Like the grain of meat, or fish, or muscle, cold rolled 6061 T-6 aluminum (such as used on a Tuf-neck) has a similar grain to it. Those layers can separate, and will exfoliate (flake) in those areas.
Intergranular, as stated in the article, is specific to high copper, such as 7075-T6 as shown in the aircraft parts above. These parts are highly stressed, flown in highly corrosive environments such as salt water, ozone, and static electricity, and severe temp changes causing condensation. Usually in SWAMP areas of the aircraft. (Severe Wind And Moisture Prone)
I would maintain that simply removing the anodizing from bicycle parts made from mostly 6061 materials, especially since they are now show bikes, will not cause intergranular corrosion in this lifetime.
As the parts are not being used ,except for show now, there is virtually no risk of anything like that.
As a prime example, DX pedals in silver were completely unprotected from the factory, as were most alloy pedal bodies. Raw aluminum. Yeah, they are oxidized now 30 years later. But, I have yet to see one that is blown apart from the inside out from intergranular corrosion. They are simply white and dull on the outside of them.
A brake caliper? Crank arm? A rim? Pro-necks?...not likely
A PK Ripper frame....maybe. Due to the welds, and stresses.
Just not gonna happen in this lifetime "On a bicycle part", unless the part is found in a junkyard. And then the corrosion is going to be every kind of corrosion but intergranular with the 6061T6 bike parts.
Stripping anno will not cause a failure on our collectors bikes. Unless you set it on the roof for about 10 years.
In fact, in most cases of aging bike parts, chrome plating on aluminum is worse than raw aluminum.
The damage that we see on bicycle parts is more typical to surface corrosion, plain and simple.
But clear anodizing does leave a very hard, scratch resistant, and corrosion resistant coating on parts, which is why it's done. But when done clear, or un-dyed, it remains a dull aluminum color at best.
If you are concerned about destroying parts by removing the ano and polishing them. Don't be.
Intergranular corrosion is very real, and a very big problem on 7075-T6 aircraft parts. But if anyone leads you to believe that this 2 year old polish job hanging in the living room is going to suddenly blow apart from the inside, and fail any time soon because the scratched and faded anodizing was removed from it....
.....then I'd say, "we'll see".....maybe in about 100 more years, or maybe less if it is tossed outside and neglected.....
The area where the quill is pressed into the aluminum is subject to high loads when people were jumpers and hard riders. However, that is still exfoliation. If you sand the areas, you will find layer after layer of thin flakes that will come off.
Like the grain of meat, or fish, or muscle, cold rolled 6061 T-6 aluminum (such as used on a Tuf-neck) has a similar grain to it. Those layers can separate, and will exfoliate (flake) in those areas.
Intergranular, as stated in the article, is specific to high copper, such as 7075-T6 as shown in the aircraft parts above. These parts are highly stressed, flown in highly corrosive environments such as salt water, ozone, and static electricity, and severe temp changes causing condensation. Usually in SWAMP areas of the aircraft. (Severe Wind And Moisture Prone)
I would maintain that simply removing the anodizing from bicycle parts made from mostly 6061 materials, especially since they are now show bikes, will not cause intergranular corrosion in this lifetime.
As the parts are not being used ,except for show now, there is virtually no risk of anything like that.
As a prime example, DX pedals in silver were completely unprotected from the factory, as were most alloy pedal bodies. Raw aluminum. Yeah, they are oxidized now 30 years later. But, I have yet to see one that is blown apart from the inside out from intergranular corrosion. They are simply white and dull on the outside of them.
A brake caliper? Crank arm? A rim? Pro-necks?...not likely
A PK Ripper frame....maybe. Due to the welds, and stresses.
Just not gonna happen in this lifetime "On a bicycle part", unless the part is found in a junkyard. And then the corrosion is going to be every kind of corrosion but intergranular with the 6061T6 bike parts.
Stripping anno will not cause a failure on our collectors bikes. Unless you set it on the roof for about 10 years.
In fact, in most cases of aging bike parts, chrome plating on aluminum is worse than raw aluminum.
The damage that we see on bicycle parts is more typical to surface corrosion, plain and simple.
But clear anodizing does leave a very hard, scratch resistant, and corrosion resistant coating on parts, which is why it's done. But when done clear, or un-dyed, it remains a dull aluminum color at best.
If you are concerned about destroying parts by removing the ano and polishing them. Don't be.
Intergranular corrosion is very real, and a very big problem on 7075-T6 aircraft parts. But if anyone leads you to believe that this 2 year old polish job hanging in the living room is going to suddenly blow apart from the inside, and fail any time soon because the scratched and faded anodizing was removed from it....
.....then I'd say, "we'll see".....maybe in about 100 more years, or maybe less if it is tossed outside and neglected.....
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