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Galvanic corrosion of Al alloy
2

Galvanic corrosion of Al alloy

Galvanic corrosion of Al alloy

(OP)
I want to couple 5xxx series and 6xxx serie Al alloys so want to know if there might be a possibility of galvanic corrosion when immersed under seewater/corrosive medium since they are both Al and i assume that they might be close to each other in the series (Galvanic Series.

RE: Galvanic corrosion of Al alloy

5XXX and 6XXX alloys are close to each other galvanically.  For full immersion, you won't need to worry about galvanic corrosion -  6XXX series alloys have mass loss and pitting that are twice or three times that of 5XXX, so their general corrosion behavior is the limiting factor.

Regards,

Cory

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RE: Galvanic corrosion of Al alloy

(OP)
Thanks so much CoryPad, although they are close to each other, i think there should be a maximum recommended pontential difference above which galvanic corrosion could be the limiting factor and i am looking for that info as well.

RE: Galvanic corrosion of Al alloy

keep in mind that with galvanic corrosion there is more to consider than just the potential difference.  The relative area of the anodic vs cathodic alloy is also important and can have a strong effect on the rate of corrosion. Small anode w/ big cathode = worse than the reverse stituation.

RE: Galvanic corrosion of Al alloy

First, the good news: As seen in the table in strider6's link, Al 5052 is so close galvanically to Al 6061-T6 that, depending on its temper (thermomechanical history), it can be higher or lower in galvanic potential.

Now, the bad news: In many 5000-series alloys, particularly those above 2.5% Mg, poor temperature control during initial processing or any exposure to high temperatures (e.g., storage in summer sunlight), segregation of Mg to the grain boundaries occurs. This Mg (or Mg2Al3 given enough time) is anodic to the α-Al solid solution matrix.  So, intense localized galvanic corrosion can occurs.  Commonly called 'cauliflower' as it resembles white florets.

A good idea to anodize or else conversion coat + paint.

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