Aluminium and steel bonding method.

[Foo Fighter]

From, https://phys.org/news/2018-04-heavyweight-solution-lighter-weight-combat-vehicles.html

 

[Hanse]

I wonder what kind of corrosion issues they'd have with that.

 

[Orionblamblam]

Galvanic corrosion happens when aluminum and steel are badly bonded... they're close to each other, but something like water (serving as an electrolyte) can get in between. If the aluminum and steel are *truly* welded to each other, then there *shouldn't* be a corrosion issue. Might need some sort of coating on the outside where the joint between the two meets the outside world.

 

[AeroFranz]

Would the difference in coefficient of thermal expansion of the two materials be a problem?

 

[Orionblamblam]

Would the difference in coefficient of thermal expansion of the two materials be a problem?

Quite possibly. So you'd want to make sure that your armored vehicle or jet fighter that uses this stuff stays at room temperature. None of that frigid altitudes or burning deserts stuff.

 

[Michel Van]

Another issue Aluminium has, is contact with metallic mercury or dustings of mercury salts.
the moment that happen with help of oxygen in air, the Aluminium corrode in hours.
its is called "rusting aluminium"

you understand now why mercury thermometers are forbidden on commercial airliners.

source:
https://www.popsci.com/scitech/article/2004-09/amazing-rusting-aluminum

http://www.madsci.org/posts/archives/mar98/889541118.Ch.r.html

 

[Hobbes]

Would the difference in coefficient of thermal expansion of the two materials be a problem?

you may be able to choose Al and steel alloys with similar coefficients.

 

[Hanse]

Galvanic corrosion happens when aluminum and steel are badly bonded... they're close to each other, but something like water (serving as an electrolyte) can get in between. If the aluminum and steel are *truly* welded to each other, then there *shouldn't* be a corrosion issue. Might need some sort of coating on the outside where the joint between the two meets the outside world.

For naval aircraft dissimilar (conducting) materials coming in contact is a huge no-no. Things like glass plies in composite, sealant, paint, and liquid shim (or all of the above) keep them from direct contact.

 

[Mark S.]

Anytime you bond dissimilar metals together you get galvanic action. Zinc or sometimes aluminum is used routinely as a donor material to provide electrons to inhibit corrosion in small buried steel pipe systems. The larger trans-con pipe lines use cathodic protections systems where direct current is used to charge the pipe. In this case it may be that iron aluminide which is created in the bond prevents the flow of electrons between the two metals. An energy barrier if you will.