7075 handling after machining

danpayneuk · Apr 9, 2021

Hey guys

Another question already!!

For you that are machining Aluminium 7075 T6, how do you handle and store your components after machining?

We have been producing some sprockets, but can't stop them oxidising before sending off to get anodised. I am at a complete loss how to stop it happening so quickly. It seems to happen really quickly, usually within a few days or in some instances much quicker.

I have been running the last lot through the tumbler, degreasing them ( wearing gloves during the handling stage out of the tank), drying and wrapping up. I have just checked on a few after noticing one had signs of oxidisation again and noticed it wasn't the only one!!!

Obviously Im doing something wrong or missing a step somewhere.

Any help would be greatly appreciated.

Thanks

Dan

Dupa3872 · Apr 9, 2021

We rinse them in clean water and blow dry as they come off the machine at every operation, I am surprised you are having trouble after doing the steps that you listed so I am at a loss for offering any further help.

Perhaps your brand of coolant is not the best for 7075 or the concentration is off.

That being said after doing all the steps you listed it's strange to me you would still be running into troubles.

Make Chips Boys !

Ron

danpayneuk · Apr 9, 2021

Hi Ron

Agree. Really don't understand it. Im far from experienced but Im pulling my hair out on this one. Forgot too say they are rinsed after been degreased also.

Will check the coolant concentration. Thought it was ok though.

Thanks

Dupa3872 said:
We rinse them in clean water and blow dry as they come off the machine at every operation, I am surprised you are having trouble after doing the steps that you listed so I am at a loss for offering any further help.

Perhaps your brand of coolant is not the best for 7075 or the concentration is off.

That being said after doing all the steps you listed it's strange to me you would still be running into troubles.

Make Chips Boys !

Ron

Bobw · Apr 9, 2021

7075 is a pain in the ass that way.

What are you "degreasing" them with. I'm going to guess that your corrosion is
caused by a PH problem.

Through mostly error, I've learned that 409 is an awesome degreaser, but it will
actually etch aluminum, its pretty acidic. This shows up as really blotchy nasty
alodine afterwards. However, degrease with Dawn, and the alodine is always nice
and uniform.

What is the next procedure? Could you just keep them oily and then clean 'em right
before you ship them out?

If they don't get a further process, specifically anodize, why not alodine them.
That'll keep them from oxidizing.

danpayneuk · Apr 9, 2021

Hi Bob

I was dipping them in diluted simple green for a 1 1/2 to 2mins in the ultra sonic cleaner. It possibly could be a PH problem.

The final product is getting anodised. Literally the last step Im on. Waiting on the last lot to finish in the tumbler and was getting ready to degrease and get packed up.

Just annoying some of the ones that have been bagged up earlier in the week have started reacted already!

Bobw said:
7075 is a pain in the ass that way.

What are you "degreasing" them with. I'm going to guess that your corrosion is
caused by a PH problem.

Through mostly error, I've learned that 409 is an awesome degreaser, but it will
actually etch aluminum, its pretty acidic. This shows up as really blotchy nasty
alodine afterwards. However, degrease with Dawn, and the alodine is always nice
and uniform.

What is the next procedure? Could you just keep them oily and then clean 'em right
before you ship them out?

If they don't get a further process, specifically anodize, why not alodine them.
That'll keep them from oxidizing.

crossthread · Apr 9, 2021

It's amazing how reactive AL is. Add an oxidizer and you have rocket fuel.

Larry Dickman · Apr 9, 2021

We clean our 7075 with either Dawn or Simple Green. However, if they are going out for anodize, you really don't need to rinse them, just blow them off. There appears to be something in our water here that reacts with 7075 and it will start to develop grayish black splotches after only a few minutes.

Limy Sami · Apr 9, 2021

Something or nothing,

This was nigh 50 years ago ao I can't remember the exact alloy, but it was quality stuff and machined like 7000 series.

Anyway, upon completion the parts were ''blown off'' with compressed air, then dipped in kerosine for a few minutes and left to drain.

It's nagging me that it was to prevent marking & staining from the coolant.

Keyepitts · Apr 9, 2021

Simple Green is a no-no on aluminum. The simple Green company actually makes (made?) a specific formula for use on aluminum aircraft because their standard product was causing aluminum corrosion issues.

jz79 · Apr 9, 2021

is that corrosion happening on machined surfaces or mostly on rolled/extruded unmachined surfaces? or is it more or less evenly distributed?

and the mistake is to degrease them, keep them oily with kerosine like Limy mentioned or WD40, it will protect them for few days till they reach anodizer, don't marinate them for too long, kerosine or WD40 has to be clean

and tumbling leaves the surface natural oxide free, so it will want to react immediately, do not keep the parts degreased and in air - that is a recipe for disaster, do not store them in contact with stainless steel, like on a work bench or a storage rack

there is also an issue of using dull tools on this material, it can cause the zinc to precipitate and cause pitting, but you'd notice the parts getting hot during machining, if they are not steaming hot during machining - this shouldn't be a factor

here are couple 7075 parts I made a week ago and they were on the bench for couple days till I got around to anodizing them, not a spot of corrosion on them anywhere:

p.s. check Ph of your coolant to see if it is in the manufacturer specified range, usually it will turn alkaline and high Ph will cause issues with aluminum

steve-l · Apr 9, 2021

My vote is a PH thing as well. I had a similar issue years ago and discovered that any salt just touching the aluminum for even the briefest period will cause this corrosion. My solution was to wipe down every part with white vinegar. It worked a treat.

Mike C. · Apr 9, 2021

Any of the typical degreasing products contain sodium hydroxide (lye), which is very corrosive to alumimum. About the equivalent of saltwater to steel. Switch to a simple soap and water cleaning and isopropyl alcohol. Should eliminate the problem.

DavidScott · Apr 9, 2021

danpayneuk said:
I was dipping them in diluted simple green

Well there you go! Stick some scraps in your Simple Green for awhile and you will see why it's a bad idea. First keep the oil out of your coolant, the less oil in your coolant the easier it is to clean your parts. I have a box way mill but only need to rinse my parts in clean water before anodizing.

trevj · Apr 9, 2021

danpayneuk said:
Hi Ron

Agree. Really don't understand it. Im far from experienced but Im pulling my hair out on this one. Forgot too say they are rinsed after been degreased also.

Will check the coolant concentration. Thought it was ok though.

Thanks

Coolant concentration can be perfect, and the PH still all buggered up due to something being alive in your coolant tank. Anaerobic bacteria grow really well under a lily pad of mung in a closed tank. Usually the result of a closed off surface due to oil, and even if you did a rinse out of the tank after a cleaning, you can leave enough alive in there to start a new batch after cleaning a tank out.
Coolant is a tool too. Maintain it so it lasts!

Dunno if the cheapo garden store PH meters would work in coolant, but you should be able to source Litmus Paper somewhere.

Has this been happening with Alloy from just one source, or has it been from various makers? More than one guy around here has reported totally different results from different sourced materials, sometimes even different batches from the same mill.

Did lots of 7075 parts both for aircraft use (which usually were etched and Alodined right away, or at least, reasonably soon) then painted, and for shiny shit, retirement gifts and the such, which were left bare metal, as machined surfaces or polished, and have not had that experience.

YYMV, but we used Simple Green for scrubbing crap of the floors, nothing else.

danpayneuk · Apr 9, 2021

evening all.

Thanks for all the replies. Looks like a few things to check then, and by the sounds of it, ditch the simple green also. I will speak with the anodisers about sending them oily components or if they need them cleaned first.

Def sounds the PH levels are worth looking into.

The components are fully machined so now raw stock faces and tooling is new so no issues there wither.

Cant wait to get this sorted. Been a nightmare!!

Duc · Apr 9, 2021

Machined 7075-T6 a few times using MB-50 coolant that is about a year old, tumbled with water, cleaned with water, and dried. Never had a problem. The parts would sit for about a month before being sent to coating.

DavidScott · Apr 9, 2021

The anodizers will not want your parts to be oily, no need to ask. If you have this much oil in your coolant you need to deal with it.

Here is some interesting info on Simple Green, it's their FAQ page, click on aluminum. PH is 8.5-9.5

jz79 · Apr 9, 2021

if you spray and wipe them with wd40 or kerosine - that will not be considered oily, and they both come off very easily with any decent industrial degreaser prior to anodizing - that is a step every anodizer will perform anyway, regardless how "dry" your parts enter their shop

neat cutting oil, like used in swiss type turning centers, that is another story, that oil is somewhat of PITA to get off of the parts, and sometimes I get parts from them with a pool of oil at the bottom of the bag - that would be considered "excessively oily" and would be a reason for an extra charge by the anodizing shop

danpayneuk · Apr 10, 2021

Duc said:
Machined 7075-T6 a few times using MB-50 coolant that is about a year old, tumbled with water, cleaned with water, and dried. Never had a problem. The parts would sit for about a month before being sent to coating.

Definitely not able to do that here for some reason. Hopefully checking the things others have suggested may allow this to happen.

DavidScott said:
The anodizers will not want your parts to be oily, no need to ask. If you have this much oil in your coolant you need to deal with it.

Here is some interesting info on Simple Green, it's their FAQ page, click on aluminum. PH is 8.5-9.5

I would be surprised if they would want then dripping with oil. Not excess oil in the coolant that is the problem as its family new.

Will have a read about the simple green. Thanks

jz79 said:
if you spray and wipe them with wd40 or kerosine - that will not be considered oily, and they both come off very easily with any decent industrial degreaser prior to anodizing - that is a step every anodizer will perform anyway, regardless how "dry" your parts enter their shop

neat cutting oil, like used in swiss type turning centers, that is another story, that oil is somewhat of PITA to get off of the parts, and sometimes I get parts from them with a pool of oil at the bottom of the bag - that would be considered "excessively oily" and would be a reason for an extra charge by the anodizing shop

Have emailed them and will give them a call Monday to check if they are happy with that. I suppose I was trying to get them as ready as possible before sending out.

DanASM · Apr 10, 2021

I have never had this happen with AL before. I wash my parts off in Kerosene and let air dry. The little bit of Kero still on the parts protects it I guess.

I dont send stuff to be anodized that often. If I did the parts would have a little Kero film on them. Never get complaints from the plater.

Usually platers have a cleaning tank they put your parts in right before they are plated.

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