Electric potential - Aluminum Steel Interface
Electric potential - Aluminum Steel Interface
(OP)
Hello All,
I have the following materials:
Material 1: Steel that is zinc flake coated
Material 2: Aluminum (Blank)
Material 3: Steel that is Z100 coated
I have a connection as such
Material 1 | Material 2 | Material 1 | Material 3
This is not exactly my area of expertise and that is why I'm writing here. I can't really explain the whole situation but the results from the corrosion test are not so good. My concern is that the electric potential between Material 2 and Material 3 is relatively high and that Material 2 gets eaten away. Could somebody maybe comment on this or guide me to some readings?
Thank you in advance
I have the following materials:
Material 1: Steel that is zinc flake coated
Material 2: Aluminum (Blank)
Material 3: Steel that is Z100 coated
I have a connection as such
Material 1 | Material 2 | Material 1 | Material 3
This is not exactly my area of expertise and that is why I'm writing here. I can't really explain the whole situation but the results from the corrosion test are not so good. My concern is that the electric potential between Material 2 and Material 3 is relatively high and that Material 2 gets eaten away. Could somebody maybe comment on this or guide me to some readings?
Thank you in advance





RE: Electric potential - Aluminum Steel Interface
Obviously, you can't.
Some boats are built with a steel hull and aluminum structure.
The trick is that the metals are joined by a band of detonation-bonded aluminum/steel, where there is no crevice in which water can accumulate.
Mike Halloran
Pembroke Pines, FL, USA
RE: Electric potential - Aluminum Steel Interface
Thank you for your answer.
My concern is that the spacing between Material 2 and Material 3 at 0,8 mm is vulnerable to accumulation of water. The Aluminum is untreated and I would think that the Aluminum will act as a anode and the zinc coated steel as a cathode and water being the electrolyte.
Do you think this idea could be valid or could I calculate the electrode potential now with data from a galvanic series that I find online?
RE: Electric potential - Aluminum Steel Interface
MIL STD 889
http://www.everyspec.com/MIL-STD/MIL-STD-0800-0899...
i was thinking it had some comments about materials closer than 0.XX volts being acceptable, but I did not find that just now.
Can you paint the aluminum with epoxy?
RE: Electric potential - Aluminum Steel Interface
Try this link and look at page 24:
http://www.google.co.uk/url?sa=t&rct=j&q=&...
Page 12 - Zinc is has a potential of -0.79v with a Copper reference
Page 12 - Aluminium covers quite a range, depending on the alloy, but let's say about -0.75v, worst case.
Mild steel - about -0.65
http://www2.sandvik.com/sandvik/0140/internet/se01...
As far as I can see, Z100 is just another form of Zinc coating.
Zinc finishes are interesting as there are many ways of coating steel with zinc, from traditional hot-dip processes through to Dacromet, Sheradizing and electroplate.
Each has its own benefits and costs. Making parts out of pre-finished steel brings its own problems owing to the presence of 'raw' edges produced by punchin, shearng, bending or other processes.
So, Al in contact with ZN: -0.79v in contact with -0.75v = difference of 0.04 volts, very low, so neither should affect the other.
However, should a raw steel edge come into contact with Al, via a coating of wet mud, salty wet mud or some other contaminant containing either or both moisture and salt, then the potentila will be = Al - Steel = -0.79 in contact with -0.65 = 0.14 and the Al will corrode in preference to the steel.
Bill