×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How to avoid corrosion between al and steel

How to avoid corrosion between al and steel

How to avoid corrosion between al and steel

(OP)
Had run across this type of questions a few times. There are a few standard methods at work (aircraft manufacture)and no one seems to question about it. Just follow the spec and do what is always be done, right?
  • For example, steel fastener in aluminum airframe. Cad plate fasteners, anodize aluminum, and wet dip fastener in primer upon installation.
  • Steel rod end into flight control rods. Cad plated rod ends with aluminum flight control rods. Wet dip rod ends threads in primer upon installation.
Are the above methods adequate? Maybe, people still discover corrosion when tearing down the old airframe at the above locations.

Now, down to my own home project and I can decide what to do without an FAA approval, nice. Since I am an engineer, I would like to do it right. See the picture, it is a firearm project.
The upper receiver is anodized aluminum 6061, 7071 or maybe 7075, unknown temper.
The barrel is 8620 steel, heat treated. Parkerized or blued.
The barrel nut is steel, heat treated. Parkerized or buled.
The shim is stainless. Not known if it is passivated.
The end of the threaed section of upper receiver had been lapped/ground to produce a true perpenticular surface reference the thread. So, the anodize on the face is gone. It is bare aluminum with touch up "cold blue". I think it is a kind or touch up alodine.
So, the way it will be assembled, what anti-seize (or compound) should I use to avoid galvanic corrosion between the upper receiver and the barrel nut or between the receiver and the barrel?
Thanks.

RE: How to avoid corrosion between al and steel

What is your electrolyte/corrodent? Are you sure you will have corrosion? Can't you anodize after lapping/grinding? I would expect thermal expansion/contraction and fretting fatigue issues before galvanic corrosion.

RE: How to avoid corrosion between al and steel

(OP)
Thanks for the reply. I am not sure if I will have corrosion, but I have concerns and that is why I am here to ask.
No, I can not anodize again. The upper receiver has been anodized. The only spot missing anodize is the lapped/ground area. I will touch up with "cold blue" some kind of gunsmith solution and I think it is just touch up alodine with black dye.

So, will this "cold blue" be adequate? It touches the barrel (parkerized steel) when they are assembled. If I use anti seize which contains graphite, will this promote corrosion?

I would not worry about any other issue since it is a proven AR15 design and I am not changing anything else.

RE: How to avoid corrosion between al and steel

I would touch up the ground/lapped area of anodic film with Alodine. Then I would quit worrying about it.

RE: How to avoid corrosion between al and steel

I would also worry more about galling or fretting.
For anti-seize I would use a good synthetic grease like Krytox.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: How to avoid corrosion between al and steel

Graphite will promote corrosion

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources