I cleaned my LMT AR with Simple Green, then cleaned it with Hoppes Gun Cleaner and finally Hoppes Oil.  I just read that Simple Green is very bad for AR's, so is my AR screwed now?  I just hosed the thing down with CLP and am going to let it sit for a little while.  Somebody help!

If you smell simple green on the ar, wash it again with hot water. and reoil.

prolonged contact with simple green will harm al. its verry important to rinse well (ie 3 times) if your going to use simple green.

With water?  That won't hurt it?  Can I not just clean it again with oil and cleaner?

Water won't hurt it. Just make sure the simple green is rinsed off completely and you thoroughly dry it. Don't forget a good coat of CLP after.

Alright, I rinsed it in steaming water in the sink, dryed it as best I could with fans, shaking and vaccume, then I doused it with CLP and am scrubbing as we speak.  Will this take care of it or do I need to do more?

Quoted: Alright, I rinsed it in steaming water in the sink, dryed it as best I could with fans, shaking and vaccume, then I doused it with CLP and am scrubbing as we speak.  Will this take care of it or do I need to do more?

that should do it but to be extra certain you should sacrifice a chicken and do 20 hail marys

Actually, you probably over did it, but no harm. It takes long term usage/exposure for simple green to affect the anodizing, as it is very weak. The places that it would attack first are things like blind holes, detent holes, screw holes, buffer tube threads, mag release holes, etc. Locations that trap the simple green in them and then it has months to start eating the anodizing. Make sure you clean out those type holes. A Q-Tip will work fine for this. As long as you've done a good rinse and re-lubed, you are probably OK.

When I finished cleaning and lubing the rifle, purple stuff rubbed off the rifle.  What in the world is this stuff?  I have noticed it before, but never really payed attention.  I have heard LMT's rifles have a purple coating on them?  Did the Simple Green take it off?

Quoted: When I finished cleaning and lubing the rifle, purple stuff rubbed off the rifle.  What in the world is this stuff?  I have noticed it before, but never really payed attention.  I have heard LMT's rifles have a purple coating on them?  Did the Simple Green take it off?

__

How does the anodizing look?

Still looks black to me

Right now the rifle is sitting in my safe coated in CLP.  How do I know if I got all the water out?  Will it start rusting from the inside out?

after a water bath, denatured alcohol works to lift the water from the metal.  If you did all you say and it looked dry, I would have nothing to worry about.

I use simple green to clean parts all the time with no rust  or signs of decay. I just do not use simple green on anything Al.

Water reduces simple green thats the reason for flushing with water.

Quoted: Right now the rifle is sitting in my safe coated in CLP.  How do I know if I got all the water out?  Will it start rusting from the inside out?

Your starting to worry too much.

What is the purple stuff coming off the rifle?

die used in the anodizing process maybe, but i never herd of that happening.

What are my options now?  Is the rifle screwed?

Well I called Gene from LMT and he said it shouldn't be anything to worry about.  I told him the dye was coming off and he said it doesn't affect the anodizing.

yeah man simple green is really bad for aluminum...

if you've rinsed it with water really well and it didn't eat the aluminum already then I would say you should be good to go.

as far as water goes...

I ran water down my barrel the other day and I thought I saw rust... used a brush with JB paste and it looks okay so far.

good luck and don't do that again

If I didn't get all the water out of the rifle, would the CLP displace it and would the lubricating properties of CLP prevent it from soaking into the metal and rusting?

Stop worrying about it.  I've never heard of a rifle being damaged by Simple Green.  This rumor started because someone in the AIRLINE industry noticed that Simple Green was damaging certain aluminum parts.  There is no real evidence that Simple Green damages AR15/M16s.  I've seen it used on MANY M16s in the past and still haven't seen any damage.  

Having said that, there's no real reason TO use it either.  There are lots of cleaners out there that work a whole lot better.

Stop worrying about it.  It's a tool.  The military abuses M16s like you wouldn't believe and they keep going and going.

Quoted: Right now the rifle is sitting in my safe coated in CLP.  How do I know if I got all the water out?  Will it start rusting from the inside out?

Your rifle is finished with a phosphate finish to prevent corrosion.  Don't stress it.  I've used M16s in the ocean and filled them up with salt water.  They don't rust immediately.  In the case of salt water, you simply wash the rifle with water and re-oil with CLP.  No problems.


A little water won't hurt your rifle.  It's not a pretty wall hanger.  It's a battle rifle.  Battle rifles weren't meant to be babied.

Thanks Colt, I feel much better

Quoted: Quoted: Right now the rifle is sitting in my safe coated in CLP.  How do I know if I got all the water out?  Will it start rusting from the inside out? Your starting to worry too much.

This happened to a buddy of mine. He cleaned his AR with Simple Green, rinsed, and repeated. He CLP’d the rifle and stored it in his safe. The next time we wanted to go shooting he went to lift his AR up and his thumb went straight through the mag well! Then the barrel fell over and separated from the upper receiver!
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Ok, not really, I’m just bullshitting!

Quoted: Quoted: Quoted: Right now the rifle is sitting in my safe coated in CLP.  How do I know if I got all the water out?  Will it start rusting from the inside out? Your starting to worry too much. This happened to a buddy of mine. He cleaned his AR with Simple Green, rinsed, and repeated. He CLP’d the rifle and stored it in his safe. The next time we wanted to go shooting he went to lift his AR up and his thumb went straight through the mag well! Then the barrel fell over and separated from the upper receiver! . . . . . . . . . . . . . . Ok, not really, I’m just bullshitting! hr

Funny  I about had a heart attack.

Quoted: Stop worrying about it.  I've never heard of a rifle being damaged by Simple Green.  This rumor started because someone in the AIRLINE industry noticed that Simple Green was damaging certain aluminum parts.  There is no real evidence that Simple Green damages AR15/M16s.  I've seen it used on MANY M16s in the past and still haven't seen any damage.

This isn't exactly a rumor.  The military has specific directives not to use Simple Green on aluminum. There is a USMC directive (might be USArmy) that prohibits use of Simple Green on M-16s, but I can't find a copy. However, below are a couple links/quotes that explain it a little more than was stated by others. There are 2 concerns with Simple Green. When it gets into cracks/crevices/between threads it causes a galvanic reaction between the steel and the aluminum. This galvanic reaction causes the aluminum to dissolve over time. The 2nd problem is hydrogen embrittlement, which causes the aluminum to become brittle by the absorption of hydrogen, reducing strength and forming micro-cracks.

Per the Response by the Navy Safety Center (End of Page):

We appreciate your information about Simple Green. Lt. David Mims, head of the Occupational and Environmental Health Division here at the Safety Center, researched the Simple Green situation. He found that the Naval Air Warfare Center (NavAir) disapproved of the use of Simple Green for naval aviation in 1993. They have a documented incident of crazing of an F-18 canopy following the unauthorized use of Simple Green. According to an official at NAVAIR, they have tested the product at least three times since 1989. Simple Green fails sandwich corrosion and total immersion-corrosion tests for aluminum. That official also said that NAVAIR recommended that commands remove Simple Green from their spaces. It's just too easy for someone who's told to clean something to grab a bottle of Simple Green off the shelf and use it on an airplane or equipment made of aluminum.

Also, August 1, 2005 Issue Aviation Today states:

The classic bottle of Simple Green cleaner has often been the subject of questions in the aviation industry, due to potential corrosion problems. Simple Green was well aware of these concerns and has developed a new forumula--Extreme Simple Green--that prevents corrosion and cleans as well as the old green solution. The problem wasn't that Simple Green was especially corrosive, but that if all of the soap wasn't completely rinsed off, then some Simple Green caught in crevices between aluminum joints could eventually create a dielectric and lead to corrosion. The old formula didn't meet formal aircraft cleaning specifications. The new Extreme formula eliminates the corrosion problem and also meets Boeing's cleaning spec, D6-17487 Revision P. Extreme Simple Green includes an anti-corrosion agent, prevents hydrogen embrittlement, and is safe to use for general cleaning and in pressure washers, parts washers, and dip tanks. Extreme Simple Green is also biodegradeable and solvent-free.

Also, the AR15/M16 aren't phosphate finished. The steel parts are, but the aluminum upper and lowers are aluminum, finished by anodizing. Lye and other type alkalines are used to dissolve and remove anodizing, and Simple Green is a mild alkaline. Even Simple Green's Website says (Under Aluminum Heading):

The aqueous-base and alkalinity of Simple Green or Crystal Simple Green can accelerate the corrosion process. Therefore, contact times of All-Purpose Simple Green and Crystal Simple Green with unprotected or unpainted aluminum surfaces should be kept as brief as the job will allow - never for more than 10 minutes. Large cleaning jobs should be conducted in smaller-area stages to achieve lower contact time. Rinsing after cleaning should always be extremely thorough - paying special attention to flush out cracks and crevices to remove all Simple Green/Crystal Simple Green residues.

You don't have to be overly paranoid about it, just make sure it is rinsed thoroughly.

Quoted: Quoted: Quoted: Quoted: Right now the rifle is sitting in my safe coated in CLP.  How do I know if I got all the water out?  Will it start rusting from the inside out? Your starting to worry too much. This happened to a buddy of mine. He cleaned his AR with Simple Green, rinsed, and repeated. He CLP’d the rifle and stored it in his safe. The next time we wanted to go shooting he went to lift his AR up and his thumb went straight through the mag well! Then the barrel fell over and separated from the upper receiver! . . . . . . . . . . . . . . Ok, not really, I’m just bullshitting! Funny  I about had a heart attack.

OK, I will volunteer to test the Simple Green Theory.
I work on aircraft, and we have plenty of aluminum laying around.

Help me come up with a test, I'll post pics etc etc.

Quoted: OK, I will volunteer to test the Simple Green Theory. I work on aircraft, and we have plenty of aluminum laying around. Help me come up with a test, I'll post pics etc etc.

Take some 2024T-3 spray it with Simple Green and speedtape the two together. Let it sit and check it once a week for signs of corrosion. Or, take a jar of Simple Green and drop an aluminum part into it.

I use Simple Green to clean steel parts on a regular basis.  Parts have been left in SG (totally submerged) for a very many days with no problems.  Partially submerged parts can be stained at the surface of SG, however.  I do make sure to get all the water off though and re-lube ASAP.  I haven't used SG for aluminum parts "just in case", but I doubt there would be any problems from a brief exposure.

Interesting things from the SG web fact:

Aluminum - Is it safe to use Simple Green on aluminum? Simple Green products have been successfully and safely used on aircraft, automotive, industrial and consumer aluminum items for over 20 years. However, caution and common sense must be used: Aluminum is a soft metal that easily corrodes with unprotected exposure to water. The aqueous-base and alkalinity of Simple Green or Crystal Simple Green can accelerate the corrosion process. Therefore, contact times of All-Purpose Simple Green and Crystal Simple Green with unprotected or unpainted aluminum surfaces should be kept as brief as the job will allow - never for more than 10 minutes. Large cleaning jobs should be conducted in smaller-area stages to achieve lower contact time. Rinsing after cleaning should always be extremely thorough - paying special attention to flush out cracks and crevices to remove all Simple Green/Crystal Simple Green residues. Unfinished, uncoated or unpainted aluminum cleaned with Simple Green products should receive some sort of protectant after cleaning to prevent oxidation.

Since AR's are hardcoat anodized, they are  not unfinished.  I see no warning as to removing anodize.

Electrolysis - as it relates to use of Simple Green or other water-based cleaners Electrolysis is the transfer of metal ions from one type of metal to another. Electrolysis needs a medium through which these ions can travel, and water is a good medium for this. Therefore, when cleaning metal parts or equipment, particularly in parts washing scenarios, it is best not to allow multiple metals to soak in the solution for any extended period of time. Evidence of electrolysis can be black or dull streaking on metal parts/equipment after prolonged soaking with other kinds of metals

Could this be the actual problem?

As for rinsing and getting it off your AR, looks like you should be OK:

Rinseability Simple Green rinses residue-free and is an exceptional cleaner for paint prep and cleaning. If you are involved in the pharmaceutical or electronics industry and have concerns regarding even microscopic levels of residue, call 800-228-0709 to receive information on Crystal Simple Green and its excellent rinseability features. Crystal Simple Green does not contain the added fragrance or color found in Simple Green All-Purpose Cleaner.

Interesting pH Chart.

I could find nothing on the supposed negative effects on anodize.  In fact, I ran a search for anodize and got no hits.  Can someone please explain to me the scientific reasons SG is supposed to be bad for anodize??

Thanks to everybody for chiming in, I am learning a lot.

This is probably safe for AR's:

industrial.simplegreen.com/ind_prod_ext_mor.php

Found this as well:

Aircraft Cleaning with Simple Green or Crystal Simple Green Many private and commercial aircraft owners and operators have cleaned their craft with All-Purpose Simple Green or Crystal Simple Green® for many years. However, these products do not have Mil-Prf (military testing) authority. The testing involves very long (168 hours in one test) soaking of various metals in the solution and then a corrosion inspection. If an aircraft owner only wants to use mil-prf approved products; he will not want to use Simple Green. Please see the additional information under "Aluminum".

Aluminum - Is it safe to use Simple Green on aluminum? Simple Green products have been successfully and safely used on aircraft, automotive, industrial and consumer aluminum items for over 20 years. However, caution and common sense must be used: Aluminum is a soft metal that easily corrodes with unprotected exposure to water. The aqueous-base and alkalinity of Simple Green or Crystal Simple Green can accelerate the corrosion process. Therefore, contact times of All-Purpose Simple Green and Crystal Simple Green with unprotected or unpainted aluminum surfaces should be kept as brief as the job will allow - never for more than 10 minutes. Large cleaning jobs should be conducted in smaller-area stages to achieve lower contact time. Rinsing after cleaning should always be extremely thorough - paying special attention to flush out cracks and crevices to remove all Simple Green/Crystal Simple Green residues. Unfinished, uncoated or unpainted aluminum cleaned with Simple Green products should receive some sort of protectant after cleaning to prevent oxidation.

So reading this, I personally would stay away from using Simple Green for cleaning ARs. You just don’t know where this stuff could be sitting in areas on your weapon that might be exposed from the anodizing being worn away.

The Aircraft version might be an alternative to cleaning ARs, but I’ll stick to the solvents I’ve used for years.

Simple Green

I still haven't figured out why the upper and lower would bleed purple dye.  Does anybody have any insight into this?  I left the CLP on over night and when I wiped it down this morning the purple came off.  Did the CLP lift it off the receivers?

Quoted: I still haven't figured out why the upper and lower would bleed purple dye.  Does anybody have any insight into this?  I left the CLP on over night and when I wiped it down this morning the purple came off.  Did the CLP lift it off the receivers?

Probably just bleeding off of the dyes used in the black anodizing process.

Quoted: I still haven't figured out why the upper and lower would bleed purple dye.  Does anybody have any insight into this?  I left the CLP on over night and when I wiped it down this morning the purple came off.  Did the CLP lift it off the receivers?

That is a bit odd, My Bushy never bled

How do you color aluminum?

There are four ways to color aluminum: 1. Dye: The freshly anodized part is immersed in a liquid solution that contains dissolved dye.  The porous anodic coating absorbs the dye.  The intensity of color is related to the thickness of the anodic film, the dye concentration, immersion time and temperature, among other things.
2. Electrolytic Coloring (a.k.a. "two-step") - After anodizing, the metal is immersed in a bath containing an inorganic metal salt.  Current is applied which deposits the metal salt in the base of the pores.  The resulting color is dependent on the metal used and the processing conditions (the range of colors can be expanded by overdyeing the organic dyes).  Commonly used metals include tin, cobalt, nickel, and copper.  
3. Integral Coloring - This so-called one-step process combines anodizing and coloring to simultaneously form and color the oxide cell wall in bronze and black shades while more abrasion resistant than conventional anodizing.  
4. Interference Coloring - An additional coloring procedure, recently introduced, involves modification of the pore structure produced in sulfuric acid.  Pore enlargement occurs at the base of the pore.  Metal deposition at this location produces light-fast colors ranging from blue, green and yellow to red.  The colors are caused by optical-interference effects, rather than by light scattering as with the basic electrolytic coloring process.  

The following procedure is for anodizing aluminum parts.  Anodizing will protect the aluminum parts by making the surface much harder than natural aluminum.  Aluminum oxide is grown out of the surface during anodizing and then becomes aluminum hydrate that is extremely hard.  The porous nature of the anodized layer allows the product to be dyed any color that is required.  The method I describe is Type II anodizing (room temperature) and gives an anodized layer of .0002" to .001" (half which is grown into the surface and half out of the surface). Parts anodized will become slightly larger by about .0005"  Type III (hard coat) anodizing is done at much colder temperatures and at higher current densities and can reach thick nesses of .002".  Type III anodized surfaces can typically only be dyed black or dark green due to the denser pore size. I do not cover hard coat procedure due to it not being in the "home brew" category due to the colder acid temp and high current density that would be required to perform it.  The anodizing guide will show you how to perform the more popular Type II anodizing (Room Temp) using the home brew hanging wire method with materials found at typical hardware and auto parts stores, (bare bones method).  Almost everything you need can be found locally except anodizing dyes and sealer which I sell small quantities on this site.  

Will do!

Quoted: Quoted: OK, I will volunteer to test the Simple Green Theory. I work on aircraft, and we have plenty of aluminum laying around. Help me come up with a test, I'll post pics etc etc. Take some 2024T-3 spray it with Simple Green and speedtape the two together. Let it sit and check it once a week for signs of corrosion. Or, take a jar of Simple Green and drop an aluminum part into it.

I'm on the edge of my seath.gif

So far the rifle functions and looks fine, I don't think anything happened to it.  Saved by CLP.

Some of the guys on GLOCK Talk have mentioned scraping the rifle and buying a whole new upper and lower.  This isn't necessary is it?

Quoted: Some of the guys on GLOCK Talk have mentioned scraping the rifle and buying a whole new upper and lower.  This isn't necessary is it?

Yet another reason why I don't spend much time over there.

Your rifle is fine.  Go shoot it.  As long it still looks black, the anodize is still there.  I never actually heard of anyone losing anodize from SG.  Lots of rumor, but no proof.

Quoted: Some of the guys on GLOCK Talk have mentioned scraping the rifle and buying a whole new upper and lower.  This isn't necessary is it?

Unfortunately, they're right, it is.
The good news, is that I will get rid of it for you, no charge. I'll even pay for the shipping to me.
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Your rifle is fine!!! I use SG all the time on my AR!!!

Rinse with water, shake dry, spray with massive ammounts of WD-40 to displace, and evaporate water.  Problems mostlikly occure with LONG TERM exposure to simple green.  Depot level armorys use partscleanrs that are proably alot more harsh on the alum/andodization than simple clean could ever be.  I would worry more about 12ga OOBuck not stoping zombie's than i would over simple green on my rifle.  Also i have used simple green to clean many a  aluminum boats with no ill effect.  there's my 2 cents

First, you have to realize that the quotes from the Simple Green FAQ aren't full explanations of the process, and some of the effects are downplayed in their response.

As far as ARs and M16s are concerned, the surface of the aluminum has been anodized using a electrochemical process. The thickness of this coating is .001-.002" thick (1-2 Mils). The coating consists of hollow cells, microscopic in size. Immediately after anodizing, the part is placed into a dye, which is absorbed into the anodizing cells. It is then sealed (hydrated), which is the process of plugging the top of the cells so that the dye remains in place. The anodized coating is not applied, but actually grown from the surface of the aluminum and consists of aluminum oxide. Aluminum Oxide is much harder than raw aluminum, which is why it is used as the grit on sandpaper and the media in sandblasting.

Aluminum Oxide provides a protective surface to the aluminum, making it corrosion resistant. Most people have seen the white powder and pin holes on raw aluminum that has been left exposed to the weather. This white powder, pin holes, is due to corrosion of the water and chemicals in the atmosphere. Anodizing is not affected by these factors. Anodizing is impervious to water, and many chemicals, but it is dissolved by alkalines. It is also hard, rated between 8-9.5 (diamond is rated as 10). This hardness adds significantly to wear-resistance of the aluminum.

That being said, Simple Green is a combination of chemicals. The alkalinity of the Simple Green slowly dissolves the anodizing, exposing the bare metal, where the water begins to corrode the raw aluminum. In the anodizing industry, chemicals containing lye, sodium hydroxide and other similar alkalines are used to strip anodizing from aluminum prior to refinishing. Simple Green is no where as strong as lye or sodium hydroxide, but it is still an alkaline and dissolves the anodizing, just much slower.
 
Its easy to test. Take your lower and drop it in a bucket of simple green. Let it sit for a couple weeks and see what you have when you pull it out. If the simple green turns black, then you know it has dissolved the anodizing, because the anodizing holds the color inside and the only way to release it is to damage the anodize cells. Once the entire cell is destroyed, you are left with raw, un-protected aluminum, which will now be susceptible to moisture and atmospheric corrosion.

The other thing that happens is hydrogen embrittlement. If you've picked up a thin piece of un-anodized aluminum that has been exposed to the atmosphere for long periods of time, and bent it, many times it will snap rather than bend. This is caused by the aluminum absorbing hydrogen from the atmosphere. Hydrogen embrittlement causes small fractures in the microscopic structure of the metal and reduces the aluminum's ability to tolerate stress.

To put this into context with AR15/M16s, using simple green will not turn your aluminum parts into white powder while sitting in your gun cabinet. What it will do is seep into the cracks and crevices, seep into screw and detent holes and weaken them over time. You may see your front pivot pin detent crack, or the wall of the lower under the selector crack though. It will take years to occur, it all depends on how frequently simple green is used and how much has seeped into these small areas.

For most of us with new uppers/lowers, this isn't going to be an issue, but for those with 20-30 year old registered receivers that cost $15,000, it is something they should stay away from to preserve their investment and keep the receiver around for generations to come.

Quoted: Some of the guys on GLOCK Talk have mentioned scraping the rifle and buying a whole new upper and lower.  This isn't necessary is it?

Not only liars, but full of s**t too! Yes, a scratch in the anodizing may expose the raw aluminum underneath but unless it is a deep scratch the base of the anodized cell is probably still there. But like any other piece of metal, if you rub it down with CLP, oil or any protectant, it will protect it from corrosion. If it required replacement, there wouldn't be 20 year old M16s being used in the military.

As many have said..don't sweat it. Using WD40 to displace the water is a fine idea if you are concerned about the cracks/crevices/detent holes. Don't worry about scratches, just run a rag with CLP over it and all will be fine.

According to this anodizing site:

You can strip off the existing anodized layer from any anodized part by placing the part in a caustic solution for an hour or so.  Just mix a few tablespoons of lye and water in a plastic container.  Wear eye protection and rubber gloves for this procedure!!  Place the part in the solution and monitor its progress.  The Lye will dissolve the old anodized layer, about .001" thick.  It takes a while for it to start breaking through the layer.  It's a little slow at first.  The first ten minutes or so not much action will be seen.  Bubbles and smut will rise up as an indicator of its progress.

That is with full power Lye, trying to take the anodize off.

According to the SG pH Chart that I posted earlier, Lye is ~10,000 times more alkaline than SG.  So I can see how it might affect annodize, but it will do it VERY slowly.  The weeks long bath senario that neilfj used is probably very correct as to how long it would take to do any real damage to AR anodize.  I think as long as you flushed it very well, there should be no problems.

Will CLP displace water as well as WD40?  The rifle was flushed with warm water then hosed down with CLP to the point I have a puddle in my gun cabinet.

your fine.

to the guy going to do the simple green soak test. weight the samples before and after soaking in simple green.

you referring to me?

Quoted: your fine. to the guy going to do the simple green soak test. weight the samples before and after soaking in simple green.

Yes, I had to type fast had a nature call.

What I would like to see is if there is any measurable loss of material from soaking AL in SG for a week or so.

OK, I will put a "Test-bed" together saturday morning at work (nothing better to do )

-edited for spelling!

Quoted: First, you have to realize that the quotes from the Simple Green FAQ aren't full explanations of the process, and some of the effects are downplayed in their response. As far as ARs and M16s are concerned, the surface of the aluminum has been anodized using a electrochemical process. The thickness of this coating is .001-.002" thick (1-2 Mils). The coating consists of hollow cells, microscopic in size. Immediately after anodizing, the part is placed into a dye, which is absorbed into the anodizing cells. It is then sealed (hydrated), which is the process of plugging the top of the cells so that the dye remains in place. The anodized coating is not applied, but actually grown from the surface of the aluminum and consists of aluminum oxide. Aluminum Oxide is much harder than raw aluminum, which is why it is used as the grit on sandpaper and the media in sandblasting. Aluminum Oxide provides a protective surface to the aluminum, making it corrosion resistant. Most people have seen the white powder and pin holes on raw aluminum that has been left exposed to the weather. This white powder, pin holes, is due to corrosion of the water and chemicals in the atmosphere. Anodizing is not affected by these factors. Anodizing is impervious to water, and many chemicals, but it is dissolved by alkalines. It is also hard, rated between 8-9.5 (diamond is rated as 10). This hardness adds significantly to wear-resistance of the aluminum. That being said, Simple Green is a combination of chemicals. The alkalinity of the Simple Green slowly dissolves the anodizing, exposing the bare metal, where the water begins to corrode the raw aluminum. In the anodizing industry, chemicals containing lye, sodium hydroxide and other similar alkalines are used to strip anodizing from aluminum prior to refinishing. Simple Green is no where as strong as lye or sodium hydroxide, but it is still an alkaline and dissolves the anodizing, just much slower.   Its easy to test. Take your lower and drop it in a bucket of simple green. Let it sit for a couple weeks and see what you have when you pull it out. If the simple green turns black, then you know it has dissolved the anodizing, because the anodizing holds the color inside and the only way to release it is to damage the anodize cells. Once the entire cell is destroyed, you are left with raw, un-protected aluminum, which will now be susceptible to moisture and atmospheric corrosion. The other thing that happens is hydrogen embrittlement. If you've picked up a thin piece of un-anodized aluminum that has been exposed to the atmosphere for long periods of time, and bent it, many times it will snap rather than bend. This is caused by the aluminum absorbing hydrogen from the atmosphere. Hydrogen embrittlement causes small fractures in the microscopic structure of the metal and reduces the aluminum's ability to tolerate stress. To put this into context with AR15/M16s, using simple green will not turn your aluminum parts into white powder while sitting in your gun cabinet. What it will do is seep into the cracks and crevices, seep into screw and detent holes and weaken them over time. You may see your front pivot pin detent crack, or the wall of the lower under the selector crack though. It will take years to occur, it all depends on how frequently simple green is used and how much has seeped into these small areas. For most of us with new uppers/lowers, this isn't going to be an issue, but for those with 20-30 year old registered receivers that cost $15,000, it is something they should stay away from to preserve their investment and keep the receiver around for generations to come.

There was a post here a while back where a guys soaked his lower in a bucket of SG for a few minutes and the SG started to bubble. When he pulled his lower out most of the anodizing was gone and the aluminum was pitted. You should now be using SG on aluminum parts. If you must get it clean then use Gun Scrubber.

if you must use SG on Al use this version.

Simple Green-Extreme Clean
MEETS BOEING SPEC D6-17487P
Extreme Simple Green® Aircraft & Precision Cleaner is a breakthrough water-based formula that cleans engines, aircraft, vehicles, metals, plastics, high-tech alloys, and parts. This non-corrosive, low-foaming cleaner/ degreaser does not contain reagents that oxidize finishes, cause rust or degrade elastic materials such as rubber or vinyl-but protects the life of hoses, seals, gaskets, paint finishes and other hard surfaces plus rinses residue-free for ease of use and protection of structures and finishes.