welding

[dan2288]

I really dont know anything about welding. I was wondering if you can weld ss and aluminum together? Or does it have to be the same metal?

 

[Dsmj89]

No you can not weld stainless steel with aluminum. You could get away though with welding mild steel and stainless steel, but aluminum can only be welded to aluminum.

 

[dan2288]

okk, thanks a lot

 

[bpestilence]

This question has been answered, but I will explain why you cannot weld steel and aluminum together.

There are three types of crystal structures that occur in metals. Many more that occur in non-metals, but only three for metals. These structures are body centered cubic, face centered cubic, and hexagonal close-packed.

The difference between the three is how the atoms of metal form together. On a macroscopic level, a FCC or BCC metal will form cubic structures, and HCP will form long prismatic hexagonal structures.

FCC and BCC can be welded together because the crystals can form into one another. In fact, steel itself can form either structure. "Martensite" is a FCC form of steel that is highly magnetic, and is achieved by rapid quenching from a high temperature. "Austenite" and "Ferrite" are less dense BCC structures that form at lower temperatures and are less magnetic. (Grain in steel is actually composed of layers of both structures)

Many metals, such a Cobalt, Chromium, Zinc, Nickel, Molybdinum, etc., are also cubic and therefore can be welded to steel and also make great alloying agents.

Some metals, however, such as Copper, Aluminum, Titanium, Lead, etc., are HCP, and will neither dissolve into steel nor weld to it. However, these metals will weld to each other and alloy each other well. (Although, for semantics, dissimilar metals being joined together is called brazing, not welding)

In the Navy, we often have to join steel to Copper alloys, however, and this may seem to be impossible. However, you can do that by first welding the steel to a form of brass (which is high in Zinc and has a very BCC structure), and then welding the Copper alloy to the intermediary metal.

 

[SpeedAddict62]

It doesn't change the answer, but:

1. Martensite is BCT - body centered tetragonal, basically an elongated BCC structure.
2. Austenite is FCC.
3. Aluminum, Copper and Lead are FCC.
4. Cobalt and Zinc are HCP.