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What happens when I put galvanized steel together with aluminum parts or put aluminum sheets on galvanized steel studs?

The question is frequently asked when two dissimilar metals are placed in contact with each other. The chart below shows the electrode potentials of metals in seawater. If two metals with different potentials are placed in contact and there is a conductive medium, such as sea water or condensation, there can be a reaction, commonly known as a galvanic cell.

The higher the electrical potential difference the greater the possibility of a reaction. In the case of zinc and aluminum, there is only a slight chance of a reaction because of the relatively small change in potential between the two metals and the formation of an insulating film on the surface of the aluminum.

One of the key factors in the reaction between dissimilar metals is the contact surface area. A severe reaction can occur when a large cathode (higher or more positive potential) is in contact with a small anode (lower or negative potential). In this situation, corrosion rates can increase dramatically.

Another key factor in the determination of corrosion of two dissimilar metals in the presence of conductive substances. In many cases, condensed water does not provide enough conductance to start the corrosion process. Whenever possible, the best solution to this type of corrosion is to prove an insulation barrier between the two dissimilar metals.

For more info on hot-dip galvanized steel in contact with dissimilar metals, refer to AGA guide on dissimilar metals.

Electrode Potentials of Metal in Sea Water

MaterialPotentail (volts)
Magnesium-1.55
Zinc-1.10
Aluminium-0.86
Cadmium-0.77
Cast Iron-0.68
Carbon Steel-0.68
Stainless Steel 18% CR 8% Ni (active)-0.61
Lead-0.57
Solder (50Pb/50Sn)-0.52
Tin-0.49
Copper-0.43
Aluminium Bronze-0.41



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Comments

Ziad Eljundi

Dear AGA Team, I hope my email finds you well and that you're staying safe. We have to fix an exterior ceiling grid in severe weather condition "Abu Dhabi - UAE" and it will be under high humidity. will it be a problem to use GI profiles with aluminium profile or their will be a risk of galvanizing? "If it is not recommended, then would it help by protecting the aluminium by powder coating it or by priming and coating the GI or steel with protection coat? And lets say the powder coated aluminium is in contact with GI Steel profile and not risk of galvanizing since the aluminium profile is protected, what is the advised screw / rivet type to be used, since it may transfer the electrons between the two. Thanks and best regards, Ziad Eljundi

Alana Fossa (AGA)

Hi Ziad, Please refer to our guide on Galvanic Corrosion which explains how to mitigate against corrosion between aluminum and hot-dip galvanizing in a n exterior humid environment: https://galvanizeit.org/knowledgebase/article/dissimilar-metals-in-contact-with-hdg

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