Hard anodizing of high silicon containing aluminum alloys by pulse anodizing

Sometimes pulse anodizing seems difficult to figure out, specially for the aluminum alloys which are difficult to anodize.

So a question about Hard Anodizing an aluminum alloy with 10% silicon aluminum Alloy to 75µm thick layer with a pulse rectifier, suggesting the current density per square feet will get the following answer.

To get 75 µm you can use different kinds of electrolytes; a suggestion would be an electrolyte with 15wt% sulfuric acid at 54 - 60F or one created from sulfuric acid and an organic acid at a lower or same temperature.

With the sulfuric acid electrolyte established you should then proceed to use 40 A/ft² for the high current density period and 10 A/ft² for the low current density period. Then depending on the geometry you should try different pulse periods. My suggestion is to start with 60 seconds in the high current density period and 20 seconds in the low period.

It is important to remember that a pretreatment with fluoride will improve your result.

Also remember that lower silicon content will give you a possibility to use a higher current density in the high current density period.

Use higher temperature than conventional hard anodizing when processing high silicon alloys, you could try using a high current density period of 20 - 100 A/ft², and pulse periods t1=t2=30 seconds.

You should always consider starting your test runs with voltage controlled anodizing, high current density period 20 - 40V and low 15 - 25 V.

If you find this article useful, Anne Deacon Juhl is available for consulting, please send an inquiry to blog@aluconsult.com

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