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topic 55301

Anodizing Aluminium LM24, A1060 -- is it possible?

June 29, 2010

Q. I am trying to anodize die cast Aluminum LM24, A1060 is it possible to get it to look good and if not what other types of finishes will work? It needs to be scratch resistant, and so far paint isn't strong enough.

Brad Adams
product designer - Carlsbad, California, USA

simultaneous July 1, 2010

A. That depends mostly on your definition of looks good. Anodized cast will never look as good as a machined wrought alloy.
Sometimes you would get an excellent casting, but normally it was from the lowest bidder. The same with extrusions.
Have you looked at powder coat and some of the two part paints which have far better scratch resistance than sprayed paints.
Even if you go to a hard, plated finish, if the initial casting is garbage, the plated part will be shiny garbage.

James Watts
- Navarre, Florida

July 1, 2010

A. Sheasby and Pinner show LM24 as: 8% silicon, 3% copper, and 1.3 % iron. They say it is recommended for protective anodizing as "moderate", not good, not very good. They say not recommended for dyeing except darker colors. They say unsuitable for bright anodizing. End of S & P.

Since you anodize aluminum and not the silicon on the surface, it is important that your preparation removes as much silicon as possible before anodizing - you must use a fluoride, maybe not HF but ammonium bifluoride. In my book, for die cast I recommend 50% nitric with one pound per gallon ammonium bifluoride. Try the process in a small way before setting up. And be aware , that the cooling rate and the recipe range of the LM24 affects the amount of silicon on the surface.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como

January 16, 2017

Q. We have HPDC aluminum part weighing 1.2 Kgs and made in LM24.
After anodizing, we observe yellow patches on anodized surface and which are random in nature. We do hard anodizing at our supplier. Need to know the reason of this as aesthetics become poor with these patches.

55301-1aThmb  55301-1bThmb

(Click graphics for higher rez photos)

Tanhaji Ghule
filters - Pune,Maharashtra , India

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