Anodising 2014A and 7075 1

[cfinister]

Can anyone help clear up some confusion I have over the suitability of 2014 T6 and 7075 T6 for anodising.

I have heard that 7075 T6 can become brittle and therefore fatigue performance is reduced when anodised or hard anodised. Conversely when browsing anodisers web sites I have noticed that 7075 is the preferred material for anodising or hard anodising as 2014 and other alloys with high copper content are succeptible to burning. The standard procedure where I work now is to avoid anodising of 7075 where used in high fatigue situations.

Can anyone help resolve my confusion?

 

[AlanD]

The copper content of the 2014A or any aluminium alloy will result in an anodised that will not resist corrosion and may actually encourage corrosion as the copper selectively etched away in the anodising bath.

 

[TVP]

The anodizing process produces a hard, brittle ceramic oxide layer (Al₂O₃) on the surface of an aluminum alloy. Under fatigue loading conditions, cracks initiate in this brittle layer, and then propagate through the base aluminum. This is why the fatigue strength is reduced.

The difference in anodizing performance among the various aluminum alloys has to do with the exact chemical composition, with copper-containing (2XXX series) alloys being noticeably worse, as AlanD explained.

 

[cfinister]

THANKYOU BOTH

I UNDERSTAND THAT 2XXX ALLOYS DO NOT ANODISE AS WELL AS 7075 BUT IS IT TRUE THEN THAT 7075 FATIGUE PERFORMANCE IS REDUCED MORE THAN SAY 2014 AFTER ANODISING, OR WOULD THE REDUCTION BE THE SAME??

 

[TVP]

The reduction in fatigue strength would essentially be the same.