How to Test Hard Anodizing

I undestand material is LM-6 not M-6.Pl.clarify

Yes it is LM-6

Hi,

LM 6 or AlSi12 (12 weight% silicon in the Al) is medium strength high ductility alloy.

It is corrosion resistant for most applications, so what is the purpose of your anodising:

anti-corrosion?

electrical insulation?

color?

reflectivity?

friction and wear?

built-in lubrication?

else?

Indicate also the process you want to use - there are more varieties than expected.

Rhabe

From what I understand of "Hard Anodising" is this : Wear resistance, enhancement to anti-corrosion, colour (added advantage, perhaps).

Your best bet would be Knoop Hardness Test to ensure effeciveness of your "Hard Anodising" process.

Nachi

Purpose of hardanodizing is colour only

Then you probably don't want to actually "HARD" anodize which is generally considered in the industry to mean what the DoD classifies as a class III anodize. It uses sulfuric acid and the resulting anodize layer before dye and sealing is a dull dark gray. Usually the only color options with class III are black, OD Green, and possibly a dark brown. If this is strictly for cosmetics, then you probably want either a class I or a class II anodize. These are much thinner layers, using different, weaker acids and there are far more color choices available.

What is it you are trying to test? colorfastness/fading? Hardness? Thickness of the oxide layer? Remember that anodize is not a coating but is in fact a chemical conversion treatment of the aluminum itself. There are going to be issues with geometry if close toleraces are involved. The aluminum oxide that forms has a larger crystalline lattice than the underlying aluminum, so it actually makes the part "grow" when it is anodized which is why some people think it is a coating. generally speaking if the anodize is .001" thick, about .0005" of it will be above the original surface and .0005" will be below the original surface.

Hi,

I agree totally: hard is not well suited for beautiful colors!

Here is an example of one of our hard anodised air-bearings (self-acting).

Very shallow spiral grooves on axial and radial surfaces (on inner - stator -part).

Coating to 10µm above turned surface (total coating thickness 20µm) and dark to dull grey appearance depending on alloy and cutting conditions.

We used unusual electrolytic composition to avoid the dangers of 20% sulfuric acid and had to accept as a consequence the dangers of high voltage (200V DC).

Hard anodised surfaces have low porosity so not well suited for printing and coloring.

RHABE

Similarly we have an Aluminum round container a cast component (Sand casting) in LM-6. One side close. The application of the container to maintain temperature about 2 degrees Celsius to 37 degree Celsius, outer surface is cover (i.e. out side OD) with insulation. Inner surface is visible.

Presently we faced problem as in aesthetic form. Patches after anodizing are sometime visible.

A criterion is to avoid any sort of oxidization in the container due to the condensing of water drops at low temperature.

So the question is process which we use at present is correct? Or we have to adopt another process which will be more reliable?

Hi,

patches after anodising are most likely insufficient cleaning or contamination after cleaning (degreasing, etching, de-smudging, rinsing),

sometimes material inhomogeneities, sometimes locally deformed surfaces, sometimes from sealing.

RHABE

You can start by studying the US DoD Mil Specs for the processes involved.

MIL-A-8625F

Mil-A-63576A

or

MIL-DTL-5541F

You can look up these and other Mil Specs at DAPS ASSIST

I agree with Rorshack. If you need to know as a contractual obligation (to meet design/test criteria) determine to what spec you should be testing.

Many test available - who are you trying to satisfy? What will assure their satisfaction?

cr3