Galvanic Reaction Between Stainless Steel and Aluminum

http://en.wikipedia.org/wiki/Image:Reduction-potentials2.PNG

The aluminium/steel system would form a little battery, and galvanic corrosion would occur; the aluminium wouldn't last long. Anodising would help, thereby delaying the inevitable.

Use a copper seperator.

Aluminium will be highly anodic to the stainless steel cathode; it is slightly less anodic to the copper. The rule is the anode should be larger than the cathode; this is employed for standard radiators for heating. The radiator panel will be steel, and the water pipe connecting the panel to the water system will be copper, in a standard household environment the connection between the two will not fail through corrosion in a very long time.

But if a copper tank is riveted together using steel rivets (does happen, at least for lecture slides anyway), the rivets will corrode in very short time when an electrolyte is present.

I have about 300 window AC's on labour camp that is no more than 200ft from the shoreline. The AC's are supported with Aluminium brackets, the brackets are secured to the walls of the buildings using stainless steel screws. The buildings are constantly bombarded with salt spray. The air is so salty that when you rub your face at the end of the day you almost sand off your skin with the salt crystals. The AC's have been in place for 5years. They have now been replaced due to the heat exchangers corroding (Aluminum very thin copper CSA big (Elastomer coating too much for cheap window units)). The brackets however were used again with no signs of major corrosion around the screws only initial oxidizing of the aluminium.

The link below is something I found quickly but gives you a basic table of andoic values.

http://www.auf.asn.au/scratchbuilder/corrosion.html

Aluminum is sacrificial to both stainless and copper. Anodizing the aluminum and passivating the stainless will slow down the galvanic action, but elimination of moisture at the joint by a secondary coating such as epoxy paint will minimize the moisture/dry cycle and keep harmful electrolytes away from the intersection. GE did this in the 1930's with its copper-aluminum joint in household refrigerators.

Lets get real.

Aluminum is fastened all the time in real life with 304 SS fasteners in the USA anyway.

There is a galvanic reaction but so weak it is still the best bet.

With a power coating on the aluminum it will be zero. But in installing, for a example, Aluminum guard rail it is normal to drill holes and insert bolts on a building site after the finish has been applied in a factory setting. The area of the hole is then bare aluminum but little deterioration occurs over years of use.

I real life.

I understand that aluminium (hey, we spell like the English in South Africa!) oxidises very rapidly once exposed to the atmosphere, so that by the time you use it we are maybe talking about Al-oxide instead? So maybe there is a difference in the reaction of aluminium with stainless steel as opposed to aluminium oxide with stainless steel?

You're telling others to "get real?"

Galvanic corrosion only occurs when an electrolyte is present (e.g. seawater).

Attach 304 stainless to aluminum, drop the assembly into a tank of seawater and watch what happens. The aluminum will rapidly corrode.

Hi Will this galvanic corrosion also occur in car's radiator and engine system? A speicific example: a rear engine vw van (diesel, lower engine block is iron/steel, upper part of engine block is aluminum). From the engine block, there is a rubber hose, then either iron (black iron pipe, or g.i. pipe), or aluminum, or stainless steel pipe. Then rubber hose again to connect to the radiator which is non-magnetic. The radiator is in front of the van. The engine is at the back. There is no direct contact between the different metals of pipes, radiators and engine block, due to the rubber hoses that link them. However, I believe some electricity runs through the entire body of the van, including the engine and liiquid of the radiator (since the battery is grounded to the van chasis). I want to replace the original iron pipes due to corrosion. I am considering using stainless steel pipe, but would that cause the aluminum engine to corrode faster? Does galvanic reaction occur here, despite the fact that there is no direct contact between the metals, and only perhaps through the liquid coolant flowing through the entire engine and radiator system? Thank you for any info

It depends also on the ratio of the surfaces; you should try to have a large anodic area (aluminum) and a small cathodic area (stainless steel).

In a marine environment there is a greater likelihood to have corrosion:

"in a marine environment, severe localised pitting corrosion to the aluminium treads has been observed where un-insulated stainless steel bolts were used to secure the treads in place. On the same ladder however, bolts with sound insulating washers did not show any pitting on the surrounding aluminium."

Bimetallic (galvanic) corrosion risks from contact with galvanised steel or aluminium

https://www.bssa.org.uk/topics.php?article=89

corrosion prevention & protection