Metals like steel and aluminum are very easy to weld together. Aluminum-to-aluminum weld or steel-to-steel weld is straightforward. Welding steel to aluminum is a common question. The answer is yes, although joining these two metals can present challenges and call for interested ones.
Due to the various metallurgical and physical properties of steel and aluminum, welding aluminum to steel is challenging. Joining them is challenging because of their dissimilarity. In addition, these two substances are almost insoluble in each other.
In the molten state, they react and form brittle bonds, making it difficult to weld them together. Together, steel alloy and aluminum alloy can be excessively brittle and unsuitable for most applications.
I will explain why it is impossible to weld aluminum to steel using conventional techniques in this blog post and the best techniques for doing so.
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Why is this difficult to do, and what are the reasons for this?
There are many reasons why welding aluminum to steel is more complicated than welding aluminum to aluminum or steel to steel.
They are dissimilar metals. If we compare steel structures with aluminum components, we notice elementary differences between steel and aluminum.
Here I presented the most important differences between the two metals that make it hard to weld aluminum to steel.
Melting temperature
Steel and aluminum have different melting points.
Aluminum melts at 1200°F; this degree of heat is not enough to melt steel. Because it is melting point is much higher than aluminum metal. Steel welding requires at least 2,500°F.
The welding arc is heated until it reaches the melting point.
If you weld aluminum to steel, you will notice that aluminum has begun to act as a liquid before the melting point of the steel has been reached; this creates a brittle compound at the weld bead, leading to weak fusion.
Heat conductivity
Aluminum is a better thermal conductor than steel.
The greater the thermal conductivity of the metal, the faster the heat reaches the colder parts of the metal, and this shows a quicker distribution of heat over the metal surface. Conventional welding techniques such as arc welding, TIG, or WIG weldings produce a lot of heat that leads to steel warp.
Current
Since the electrodes must alternate between positive and negative charges, alternating current is required for TIG welding.
The positive electrodes must destroy the oxide layer, while the negative electrodes are responsible for melting the aluminum itself.
You cannot destroy the oxide layer if you TIG weld with direct current. This leads to the formation of a partially molten oxide layer on the filler metal, which leads to contamination of the weld.
Intermetallic compounds
Since there is no fusion or insufficient aluminum and steel, this has disadvantages that make it difficult to weld these two metals.
This leads to the formation of brittle intermetallic compounds. The connections are weak, which leads to the appearance of weak points and breakage.
By what method is it possible to do this if traditional methods are not suitable?
The best ways to weld two metals are via bimetallic transition inserts and dip coating. Let’s look at each method of different welding metals.
Bimetallic transition inserts
Advantages and Disadvantages of Bimetallic Transition Inserts
The bimetallic transition insert method is known for its quality welding joints. It also relates to joining dissimilar metals like joining aluminum to steel. This can provide the same weld strength as weld steel or aluminum.
The size and shape of the bimetallic transition insert may vary depending on the welding process, and not all bimetallic transition inserts may be suitable for all types of welding. The insert is usually made of a solid aluminum part with an equal amount of stainless steel connected directly to aluminum.
You do the welding by connecting aluminum to aluminum and the steel side to steel. To join steel and aluminum together to create a bimetallic insert, many methods can be used, such as:
- Explosion welding.
- Friction welding.
- Flash welding.
- Hot pressure welding.
To prevent overheating inserts, the aluminum to the aluminum component is initially welded. It requires less heat than welded steel. In addition, welding the aluminum part at the beginning helps to create a larger heat sink when welding steel afterward.
After you finish the first welding, the aluminum parts absorb heat to prevent the inserts from overheating as you continue to fuse the steel to the steel portion. This technique is used when welding aluminum to steel pipes, tubes on heat exchangers, and other structural applications.
Dip coating
Advantages and disadvantages of dip coating
Dip coating is the other method for welding aluminum to steel. It welds aluminum to steel coated with an aluminum-silicon alloy using hot dip aluminizing.
The process can be explained as dipping the steel into the weld pool of molten aluminum so that it forms aluminum-coated steel.
Melted aluminum in liquid form connects with the steel surface and cools at it. This ensures that no soft intermetallic compounds are formed during welding.
As it is not direct welding of dissimilar metals, the welded aluminum to steel is solid.
Then, aluminum that connects with steel can be welded to aluminum material. For it, arc welding would be better to fuse aluminum-coated steel part to aluminum metal to finish this welding process.
It would be best if you made sure that the arc welding is not in contact with the steel to prevent the aluminum coating as it can quickly burn through the aluminum coating, which will lead to the melting of steel and the formation of brittle intermetallic compounds with aluminum. Only the metal component should be exposed to the arc.
Then the molten aluminum component of the welding bath should be directed to the aluminum coated with steel.
Dip coating allows for connecting two dissimilar metals. But it is mainly demanded in seam sealing rather than structural applications. They are less widely used than welding aluminum to steel with bimetallic transition inserts.
Frequently Asked Questions
Can you weld steel onto aluminum?
No. Welding steel with aluminum is relatively easy compared to welding aluminum with steel. Because of the difference in the melting point of both metals and steel has a higher melting point than aluminum. When heated steel comes into contact with aluminum, aluminum loses shape and begins melting.
Can you MIG weld aluminum and steel together?
Traditional methods such as Tig, Arc, and Mig are not used. Tig weld is not used because Tig welding produces a lot of heat that makes the steel to warp. Because of it, Mig weld is not recommended to weld aluminum to steal.
What metals cannot be welded together?
To find out which metals cannot be welded together, we can consider an example of why it isn’t easy to weld aluminum to steel. Steel and aluminum differ in melting point, thermal conductivity, and current. Metals similar to steel are metals that must be avoided for welding with aluminum.
It is challenging to directly weld a metal like magnesium, titanium, copper, or steel to aluminum. This is due to the formation of brittle compounds when the intense heat of arc welding melts aluminum.
These crystallized structures are easily broken since they are so crispy. Due to their fragility, any steel part directly welded to aluminum will have an extremely weak weld bead.
What kind of welder do I need for aluminum and steel?
It depends on which method you are going to use. If you plan to weld aluminum to steel through bimetallic transition inserts, explosion welding, friction welding, flash welding, and hot pressure welding can be used to finish the welding process. While if you choose to join aluminum to aluminized steel, arc welding is the preferred option.
Depending on which method you will use to complete the welding, purchase a welding machine designed for this method.
Conclusion
We found ways to weld aluminum to steel, but it is only possible to do it with additional components. It leads to the formation of brittle intermetallic phases, resulting in weak fusion.
Bimetallic inserts provide more significant support for structural applications. You can use this technique for little or large tasks, such as joining an aluminum pipe to a steel pipe or connecting a cabin made of aluminum alloys to stainless steel decks on a ship.
But it would be best if you found the inserts that fit your welding project. If it is impossible to find suitable inserts, dip coating is an excellent alternative to welding aluminum to steel.
Consider changing your plan to eliminate the need to weld aluminum with steel. For example, to replace one of the materials or to connect them using mechanical fasteners.
Read How to weld aluminum without gas