Can You Weld Aluminum To Steel? Understanding Your Options

Aug 31, 2020

Whether you’re working on a personal project or are fabricating a large piece of equipment for a commercial client, you may be wondering if it’s possible – or a good idea – to weld aluminum to steel. So in this guide from Vern Lewis Welding Supply, we’ll take a deep look at this subject and explain what you need to know.

Steel And Aluminum Should Not Be Welded To Each Other Directly

It is never a good idea to try to weld aluminum and steel together directly. Steel and aluminum alloys have very distinct metallurgical and physical properties, and cannot be joined directly.

Firstly, steel has a much higher melting point than aluminum. In addition, these metals are not soluble with each other – when they flow together in a molten state, brittle intermetallic compounds are created that create a weak joint.

The brittleness and weakness of these joints mean that it’s completely impractical to weld steel and aluminum together directly in any kind of industrial application. The joint would fail quickly.

But is it completely impossible to weld aluminum to steel? The answer is “no.” With a bimetallic insert, it’s possible to reduce intermetallic formation and fuse steel and aluminum with welding.

Bimetallic Steel And Aluminum Inserts Can Be Used To Weld Aluminum To Steel

As the name suggests, a bimetallic transition insert is a piece of metal that is made of one part steel and one part aluminum. This insert is placed between the aluminum and steel components.

Then, the aluminum portion of the insert is welded to the aluminum structure, and the steel portion is welded to the steel structure. The aluminum is usually welded first so that there is a larger heat sink available when the steel is welded, due to the high melting point of steel.

The result is a strong weld that will have minimal brittle intermetallic compounds. If you must join aluminum and steel together with arc welding, a bimetallic transition insert will provide the best structural integrity for the joint.

Rotary Friction Welding Can Be Used In Some Situations

This is not as common as using bimetallic steel and aluminum inserts, and cannot be done on all workpieces. In rotary friction welding, one workpiece is rotated while it’s axially compressed against the other workpiece using specialized equipment.

Friction and heat begin to build up between the workpieces, which causes the plasticization of the interface material. Then, the two workpieces are compressed together.

This is a “solid-state” joining process, which is done at a much lower temperature compared to welding. Neither metal enters its liquid state, so fewer intermetallic compounds are produced in the joint, keeping it strong and durable.

Adhesive Bonding, Brazing, And Metal Fasteners Are Typically Preferred To Welding

So, is welding aluminum to steel using a bimetallic transition insert a good idea? In most cases, no. The process of fabricating a bimetallic transition insert for a particular job is not simple or cheap. It’s only recommended when no other joinery method is possible.

In most cases, it’s easier to join steel and aluminum using other methods, including adhesive bonding, brazing, or the use of metal fasteners.

For joints that will not experience much stress or wear & tear, the use of adhesive bonding is a great option, and it’s very simple and straightforward to bond the steel and aluminum components together.

Brazing is also commonly used, since it allows the metals to be joined without exposing them to the extremely high temperatures that cause intermetallic compounds to be formed. Brazing forms a very strong joint, and is faster and more straightforward than joining steel and aluminum using bimetallic transition inserts.

Finally, the use of metal fasteners is more than adequate for many structural fabrication tasks. Using bolts, rivets, and other high-quality fasteners allows the metals to be joined together without any exposure to heat. However, care must be taken to avoid galvanic corrosion. The aluminum must typically be painted or coated to insulate it from the steel and prevent this.

Know What Joinery Method Is Right For Your Project!

When considering the joining of aluminum and steel, you should consider the required strength of the joint, the budget for your project, and a number of other factors.

Rotary friction welding or the use of a bimetallic transition insert may be appropriate – or you may simply want to choose brazing, adhesives, or metal fasteners. The choice is yours, so consider the situation carefully.

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