Using arc welding, you can easily join aluminum to most metals, including titanium, bronze, copper, magnesium, and steel. However, it’s a fact that arc welding develops brittle intermetallic compounds that aren’t good for the joint’s strength.
Two techniques are created to join aluminum with steel through arc welding. Besides, the purpose of these procedures is to separate these metals from one another during arc welding. In this way, these techniques stop metals from forming rough intermetallic compounds, thus improving the durability and strength of joints.
One of these techniques is to utilize bi-metallic transitions through which you can join aluminum with steel without forming compounds. Moreover, it lets you join steel with stainless steel and aluminum with aluminum. Other than that, the second way is to use silver soldering for joining aluminum and steel with arc welders.
The question arises: Can you weld aluminum to steel by TIG welding? The answer is complete no because it can produce brittle compounds. So, before learning the two procedures for joining aluminum and steel, we will first discuss why we can’t do this by applying TIG welding.
Why isn’t it possible to join aluminum with steel using TIG welding?
We all know how beneficial TIG welding is due to its ease of use and variety of applications, but when metals are similar. The reason is that TIG welders generate arcs that melt the base metals and join them. Moreover, this welding technique works exceptionally well if you have to join two similar metals of the same thickness as it produces excessive heat.
Let’s say you weld two unlike metals using a TIG welder, then what happens? The metal with a minor melting point will change its physical state earlier than the other one. In this way, it will be difficult to control the process because welding demands both metals to melt simultaneously to create even and strong welds.
It will be hard for you to weld those metals with remarkable differences in physical properties. Moreover, the thickness of metals has a significant impact on the quality of work delivered. If we see the properties and melting points of aluminum and steel, there is a huge difference. That’s why it isn’t worth it to TIG weld aluminum and stainless steel.
What are the disparities in the properties of steel and aluminum?
As we have discussed above, there are incredible dissimilarities between aluminum steel, making TIG welding unfriendly for their joining. If we look at the melting point of aluminum, it is 1221°F, whereas steel has a 2500°F melting point. It shows that the aluminum will melt with less than half the melting point of stainless steel.
To make the situation even worse, the melting point of the aluminum surface having oxides is 3700°F. So you can guess from that how difficult it is for the welder to weld these two metals. The matter isn’t over there because aluminum is five times more conductive than steel. It means if you heat one point of the melt, it will spread to the other parts much faster than steel. Which makes aluminum prone to wrap.
But if aluminum has a layer of oxide, then this layer will act as an excellent insulator of heat. Therefore, you have to provide more heat that causes the stainless steel to wrap. So, if you’re going to weld scrap aluminum to steel, the quality of welds will go down and cause further complications.
In addition to that, the two aluminum base metals are joined by the TIG welding technique using AC because it offers reverse polarity. When the polarity is negative, it clears oxides blasting it, and when it becomes positive, it metals aluminum to accomplish the task. But TIG welding of steel is done with DC, which uses positive polarity.
From this, it is clear that TIG weld aluminum to steel isn’t suitable with DC as it uses only +ve polarity, which will not clean up oxides from the aluminum surface. Moreover, the oxide will also melt in DC TIG welding and get mixed in the filler metal, thus creating contaminated weld. All these complications show that applying the TIG welding technique isn’t suitable for joining aluminum to steel.
Techniques you are applying to weld aluminum to steel
Here are the two techniques:
By bi-metallic transition inserts
Have you ever heard of a bi-metallic transition insert? If not, then don’t worry. You are not alone. Generally, it’s made up of already joined two metals by another metal, excluding arc welding. The metals in the bimetallic transition insert can be aluminum and steel. Moreover, by using bimetallic transition inserts, you can easily weld aluminum to steel without any obstacles.
You can apply TIG welding using bimetallic transition inserts. As you can arc weld aluminum side with aluminum and steel side with steel. Besides, you must be careful about the process. Because providing excessive heat can melt both aluminum and steel sides of the insert, which can create a brittle intermetallic compound.
We suggest welding aluminum to the aluminum side of the bimetallic transition insert first. As aluminum has a lower melting point. It is so because if you join the steel side of the bimetallic transition insert with steel early, then the chances are you will burn the aluminum side of the inert as well. Which is not suitable for the project.
By coating the steel
Another proven and excellent way to weld aluminum to steel is to coat the steel with that metal which is easy to weld with aluminum. Two standard procedures for accomplishing this task are:
- The dipping of stainless steel in hot and molten aluminum
- And covering of layer of steel with silver solder
Both these ways are good to prepare steel for welding with aluminum. However, make sure that welding coated steel to aluminum heat melts the coating, which acts as a filler to join both aluminum and steel. In case if the steel gets melted, then it gets merged with aluminum and hence produces brittle intermetallic compounds. And that is why the quality of welds produced is not so good.