Rami

Topic: Aluminum versus Titanium contacts for type 3 anodizing

I am working on a project where we require a type three hardcoat anodized finish on a 7075-t6 part. I am the end user and not the platter. We have been receiving parts that are extremely burnt over the past couple of month. We have been working with the platters to try and resolve the problem. We have tried all sorts of things from changing the ramping time and current. However our parts come back extremely burnt. I have wall thickness in places that measure as thin as .040” that completely dissolved after the anodizing process. The platters at one point where convinced that the parts where not 7075, yet we sent them out to a chem lab and they confirmed indeed we received the right chemical composition for 7075.

The next step that the platter wants to try is to replace the titanium contacts with aluminum contacts to enhance the electrical connectivity.

Do you have any thoughts???

DustinGebhardt

Re: Aluminum versus Titanium contacts for type 3 anodizing

I've always used aluminum contacts for my Type III work.

And regarding your wall thickness, remember that anodizing converts the existing metallic aluminum into aluminum oxide. So, it will continue to consume the metal Al as it forms the oxide. If you have a very thin part, it is possible that the entire piece will be converted to the oxide. And this process is never 100% efficient, in that some of the aluminum will be dissolved into the anodizing bath.You may want to consider this and redesign your part so that you yield a finished piece with the dimensions you require.

-Dustin Gebhardt, CEF

Advanced Manufacturing/Finishing Engineer

Moen

Sanford, NC

Rami

Re: Aluminum versus Titanium contacts for type 3 anodizing

Hi Dustin,

We have a machine to set of drawings just like MIL-A-8625F suggests. The anodized film is 2thou thick, and we machine 1thou under so we get the correct tolerances after. Yet in the places that burn their is no aluminum left period.

From what I have read their is a minimum radius to hold on the corners of 1/16, yet their is no minimum callout in the MIL spec on wall thickness. What was the thiness wall thickness you have anodized using type 3 with a 2 thou thickness?

Do you also use a mechanical fastner when using aluminum contacts to assure the contact point does not become anodized?

DustinGebhardt

Re: Aluminum versus Titanium contacts for type 3 anodizing

I don't recall off the top of my head what our thinnest wall dimensions were. I think most of our stuff was 1/8" or thicker.

Regarding the contacts for the racks, both titanium and aluminum have their pros and cons. With aluminum you must strip and clean the contacts after each and every cycle. This is usually fairly simple, most often consisting of the normal etch and desmut steps of the normal aluminum pretreatment. And the contacts must be fairly strong to avoid any movement of the part during the process. I always recommended the use of at least 2 opposing contact points, preferably 3 or more contact points. If the part can wiggle on the rack, it is not secure enough.

-Dustin Gebhardt, CEF

Advanced Manufacturing/Finishing Engineer

Moen

Sanford, NC