Contact US

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!

*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

Cast aluminium surface

Cast aluminium surface

Cast aluminium surface


Noticed some of cast aluminium part that was machined into the size had kept in warehouse and found colour change.
Attached images show before and after change.
Is it being oxidised?
If so, as this part is used as heat sink where the LED boards will be mounted on, I am wondering if the oxidised surface would affect on thermal and electrical conductivity ?
Any comments/advice will be much appreciated.


RE: Cast aluminium surface

Yes - this is oxidation.
Yes, this will affect both thermal and electrical conductivity.

Good news is - it can easily be removed. Depending on how "clean" you want it to be, a manual or power driven wire brush will remove most of it (and smear a bit of it open on/in the surface), or chemical cleaning (NaOH will remove the oxides, but too concentrated and it will remove base metal as well).

RE: Cast aluminium surface

If you apply a paste or compound to assist heat transfer, and you don't rely on this for an electrical connection then you may not need to do anything.
I would suggest that you look at using a flap wheel made with a flexible abrasive like ScotchBrite just to clean them some.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Cast aluminium surface

Thanks for the advise Kingnero and EdStainless.

Is there any way to prevent them to be oxidized? After machining them, we keep them in the box indoor.


RE: Cast aluminium surface

Wipe some oil on them. Without knowing your specific heat transfer compound, I would recommend a silicone based oils as it will likely be compatible with the compound so you won't need to remove it before assembly. DOT 5 brake fluid (not 5.1) is a really inexpensive source of silicone oil...

RE: Cast aluminium surface

There are dips intended for use with Al, sort of oils buy really a corrosion inhibitor in a liquid carrier.
Contact one the people that supplies RP oil or VPI products.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Cast aluminium surface

First, we are not looking at a cast aluminum surface. It is a machined surface on a cast part. The corrosion displays the pattern of the machining marks. It appears to me that the high points of the marks are corroding because they touched something that is causing the corrosion. There are even what might be fingerprints showing. The solution is to control the contamination source or protect the surface with a suitable oil or coating. Dirty rags might be one cause.

RE: Cast aluminium surface

Comp, good point, we might even go back a step and ask what coolant they using in machining and are they keeping it clean and refreshed properly?
How are the parts cleaned after machining?
All of this matters.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

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! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close