Can You Weld Aluminum to Steel

Can You Weld Aluminum to Steel?

Aluminum and steel have very different properties, but they can be welded together. Have you ever noticed how when you mix together aluminum and steel, the two metals react? The two metals will fuse together, forming aluminum steel. And, in order to weld aluminum to steel, you’ll need to use two different welding processes.

Can Steel be Welded to Aluminum?

 Though conventional welding techniques like SMAW, GMAW, and GTAW cannot weld steel to aluminum, there are some alternatives that might provide acceptable results.

In this article, I’ll be discussing the processes that can weld two dissimilar materials together, what needs to be taken into account, and what alternatives are available.

Why You Can’t Weld Steel to Aluminum

One of the main reasons that you can’t weld steel to aluminum with the welder in your garage is that the difference in melting temperatures between the two metals is too great. In the end, I used a steel filler. The aluminum was melting away before the steel even formed a puddle, so I added a lot of steel filler to get the two materials to meet up.

The aluminum will typically melt long before the steel reaches its melting point. Even if you can get the two metals to pool together, they won’t fuse. If you try to weld steel and aluminum together, you’ll just end up with a bunch of steel that’s only lightly held together by messy, garbage aluminum.

This required no force to break apart. Even though it looked like the material was stuck together, the metals just didn’t fuse. The differential thermal expansion between aluminum and steel creates considerable stresses that cause welds to crack as the metal cools. Some other reasons why welding steel to aluminum is not effective are their different thermal conductivities, lattice transformations, and the formation of subsidiary precipitates.

Point is, that you can’t weld it using TIG, MIG, or stick welding unless you use bimetallic transition inserts.

Bimetallic Transitions

A bimetallic transition occurs when two dissimilar metals are pushed together to a point where their properties are altered. If the two metal atoms have an opposite charge, then there will be a net attraction between the two, causing some molecules to condense into a solid. 

The first part is the bimetallic itself, which is a thick insert of metal in an insulated housing. The second part is a big thick magnet. You put the insert in the housing and weld the end, and then you put the magnet on top and weld it to the other end.

Bimetallic Transitions

Then you use a regular GMAW or GTAW process to join the steel to the steel, and the aluminum to the aluminum.” These inserts are typically bonded using hot rolling or hot pressure welding techniques (explosion welding).

They can actually withstand a considerable amount of force, and the welded connections with these inserts are very strong. Some MIL specs state that these bonded inserts should have a tensile strength of at least 1/4 that of aluminum, although they usually come in at around 1/2.

Aluminizing

This isn’t a word that I just came up with.  Aluminized steel is a metal that is commonly hot-dipped with an aluminum-silicon alloy. There are other methods of achieving the same result, like galvanic coating, but hot-dipping is the most common.

Welding large pieces of steel with large pieces of aluminum is not practical. I’m bringing this up because there seems to be some misinformation on the internet about this. A few sites say that you can weld a block of aluminum to a piece of aluminized steel.

There is no way to weld aluminized steel to regular steel. The reason this doesn’t work is that when the temperature gets hot enough to melt the steel underneath, the thin aluminum coating has already been burned away.

Brazing

It should be noted that some expertise is necessary to produce successful results with brazing. When you need to join steel to aluminum, brazing may be a viable option. Brazing, however, will not produce a joint with as much strength as explosion welding. You will need a good amount of surface area for the pieces to adhere, and a strong mechanical fit will help to keep things from falling apart.

Brazing

Assuming that you have a basic understanding of how brazing works, here is a brief overview of the process:

  • Begin by wetting the steel with a 56% silver braze.
  • Brazing alloys like Aluxcor 4047 work well for joining aluminum to wetted steel.

This two-stage method is likely to produce better results than a single-stage brazing process. The single-stage brazes are not as strong because the braze itself is quite soft. Therefore, you won’t get as much holding power.

Bonding

If you’re looking for a stronger connection, using epoxy or another kind of bonding agent might be the way to go. JB Weld is a great way to fix this issue, but you need a lot of surface area for it to work properly.

Be sure to take your time cleaning both pieces thoroughly, and ideally scuff up the surfaces to be bonded for more holding power. 3M industrial structural epoxies are great for high-end products, but they can be expensive and have long cure times.

Mechanical Fastening

If it is at all possible, please use mechanical fastening. The easiest way to join aluminum to steel is to just go to the hardware store. There is no doubt that mechanical fastening is the best way to join dissimilar materials. It is cheaper, faster, and easier than any other method.

Mechanical Fastening

Galvanic Corrosion

Be aware that steel is usually prone to rusting, while aluminum is considered to be corrosion-resistant. Joining the two metals together and adding sahlt water will cause significant corrosion of the aluminum. This is due to galvanic corrosion.

The steel and aluminum create a galvanic cell, with the steel acting as the cathode and the aluminum acting as the anode. The electrolyte provides a medium for ion migration, resulting in the oxidation of the anode (aluminum). The aluminum will corrode in the area where it contacts the steel if it’s exposed to saltwater.

This can cause problems in many applications where salt is present. To avoid electrical current between the two materials, isolate them using paint or plastic. You can use a continuity tester on a multimeter to check that the metals are properly isolated.

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