When you’re first learning to weld, you’ll spend a lot of time working with steel. It’s a durable workpiece that you can use to practice a number of different welding techniques. It is used in a variety of applications from industrial builds to creative projects around your home and personal workspace. 

But, not everything can or should be built using steel. Eventually, you’ll want or need to work on a project that requires you to move on and start learning to work with other types of metal. All professional welders should be able to work with many different metals and know which welding procedure to use and when.

Welding aluminum can be a little bit more challenging than welding steel. As you’ll learn below, there are several key differences when it comes to working with these types of materials. You’ll need to use some special procedures and materials to get quality results.

Here are some helpful tips and key differences between welding aluminum and welding steel.

Metal Properties: Aluminum vs. Steel

When it comes to steel and aluminum, they couldn’t be any more different. Aluminum is less dense and weighs less than steel. The big difference, though, is the thermal conductivity. Aluminum can get very hot, very fast. In fact, the rate of heat transfer is nearly six times greater than steel. 

As a result, you’ll find aluminum welds solidify much faster than steel welds. When you’re welding aluminum, you need to be careful. The melting point of aluminum is about 1221° F compared to the melting point of steel, which is 2500° F. As you can see, it’s a lot easier to burn through a piece of aluminum than it is when working with steel.

What makes aluminum even more challenging is the thin outer oxide layer it has. You’ll need to make sure to clean this off before starting to weld aluminum. The melting point of this layer is 3700° F. Unlike steel, which can be welded without cleaning off rust or dirt, aluminum needs to be thoroughly prepared with a wire brush to get your desired results.

3 Key Differences Between Welding Steel and Welding Aluminum

As you can probably tell, working with aluminum requires a bit more focus and effort than it does when working with steel. Today aluminum is used in the manufacturing, automotive, and aerospace industries. Understanding what makes welding aluminum different from welding steel is something every welder (enthusiast or professional) needs to know. 

Here are the three biggest differences between welding aluminum and steel.

It’s Harder to See Molten Aluminum

When you’re working with steel, it’s easier to tell how far along you are in the weld. As steel heats up and melts, it changes color. You’ll start to see a silvery color that is noticeably different than the color of the unmelted steel. Experienced welders will use this distinction to judge how far along they are in the weld.

When you’re working with aluminum, though, you can’t really use that quick tip. You see, melted aluminum looks almost identical to solid aluminum. There’s really no difference between them in color. 

This is why you need to be more focused on the task at hand when welding aluminum. If you don’t pay attention, it’s easy to overapply the heat source and burn a hole through the aluminum workpiece.

Aluminum Needs More Prep Work

Before you start welding any metal, you really should spend some time cleaning and prepping it. Just because you can MIG weld metals like steel without cleaning off the dirt and rust, doesn’t mean you should. If you’re going to be welding aluminum, get prepared to put a little more time and effort into getting the workpiece ready to weld.

Cleaning and pretreating your materials will ensure a stronger and more durable weld. When you’re working with aluminum, you need to remove the dirt, oil, and other impurities just like you should with steel or any other metal. Once it’s clean, next you’ll need to remove the oxidized layer from the surface. The best way to do this is with a wired brush. Just make sure the brush is used exclusively on aluminum. If it’s just a general shop brush, you’ll just be adding more impurities to the metal you just cleaned.

Once the oxidized layer is removed, get to work right away. Because the metal is exposed to oxygen in the air, it will start to reform that oxidized layer, immediately undoing all of your work.

Aluminum Gets Hot Really Fast

Heat has a much easier time spreading through a piece of aluminum than it does through a piece of steel. Since the thermal conductivity or rate of heat transfer is so much greater, this creates some challenges when welding aluminum. You’ll find that the weld solidifies much faster than it does on steel. 

As a result, you’ll need to keep a steady travel speed and keep the welding gun moving along the weld. If you’re not careful, it’s easy to distort the weld area.

How to Weld Aluminum

MIG welding aluminum is much different than steel. While the process is similar, you’ll need to use different shielding gases and use specialized machines that can MIG weld aluminum. Once you’ve got the correct equipment, follow these steps:

  1. Start by cleaning the aluminum and removing any grime, dirt, or oils
  2. Use a wire brush, grinder, or file to remove the oxidized layer
  3. Clamp your workpieces together tightly to avoid any gaps in the weld area
  4. If you want to make it easier to weld aluminum, you can preheat it by applying heat to the surface with a propane torch until it reaches 300-400° *(this step is completely optional)
  5. Turn on your welding machine and start the shielding gas
  6. Set the amperage on your welding machine. You’ll want about 1 amp per 0.001 inch
  7. Double-check the settings on your machine, shielding gas, and clamp
  8. Start your arc and begin welding
  9. Once you see the puddle starting to form, begin moving the torch, keeping a steady and consistent travel speed.
  10. Turn off the gas and welding machine when complete

How to Weld Steel

Other than the additional prep work, the process of welding steel is very similar to the steps involved with welding aluminum. Here’s how to MIG weld steel:

  1. Clean and prep the workpieces, removing any rust, grime, or oils
  2. Position your workpieces and get ready to weld
  3. Attach the ground clamp to your workstation
  4. Turn on the welding machine and shielding gas
  5. Adjust your welding machine’s voltage and wire speed to the appropriate settings (there should be a chart on your machine to reference)
  6. Make sure the correct amount of wire is protruding from the tip of the torch. If it’s too long, just cut it down to the right length with some wire cutters or pliers.
  7. Start welding the materials
  8. Once complete, turn off the shielding gas and welding machine 

What Shielding Gas Should You Use to Weld Aluminum or Steel?

Shielding gas is one of the most important factors when welding steel or aluminum. Without it, it would be impossible to get the job done. The role of shielding gas is to “shield” the weld pool from non-inert gases in the atmosphere like oxygen which could cause the metal to rust and weaken the weld.

Shielding Gas for Steel

If you’re going to be MIG welding carbon steel, you’ll have a few different options for shielding gases. This type of welding can be done with just carbon dioxide alone. This will produce the deepest weld penetration possible. However, it will also create a very rough weld and more smoke than you will want to be dealing with. 

The most common blend of gasses welders will use is a 25/75 mix of carbon dioxide and argon. This will produce the best all around results when working with steel. There are other combinations of shielding gas you can use, though. Another popular option is a mix of carbon dioxide, oxygen, and argon.

Shielding Gas for Aluminum

If you’re going to be welding aluminum, the options for shielding gas are very specific. For pretty much any piece of aluminum, you’ll need to use 100% argon as your shielding gas. 

There’s only one exception to this, and that’s if you’re working with aluminum that is thicker than ½ of an inch. In this case, you’ll need to add some helium to the mix. This is like adding a little bit of gas to fire and will help make the temperature rise faster on a thick piece of aluminum.

When to Work With Aluminum

Now that you know more about welding aluminum, you might be asking yourself when to work with steel and wondering why you would choose this slightly more complicated material. Since it’s a bit more challenging than working with steel, it’s good to know when it makes the most sense to put the extra effort into welding aluminum.

Is Weight a Factor?

If you need a lightweight metal and weight needs to be considered, aluminum is your best choice. Despite the fact that the metal is soft and lightweight, it’s still very durable. This is why it’s such a popular choice for airplanes and automobiles.

You Want To Avoid Rust and Corrosion

If appearances matter and you don’t want rust or corrosion ruining your hard work, stick to aluminum. It’s a great choice to use when you’re being mindful of how the final product looks. An added bonus is that aluminum is also pretty easy to paint.

If You Want Something More Flexible

Aluminum is more elastic and is easier to bend and manipulate when compared to steel. Even when it’s been shaped, it still maintains its durability and strength.

When to Work With Steel

For the majority of projects, steel will be the most dependable and easiest type of metal to use. While there are certain times when you need lightweight aluminum instead, steel offers several benefits over aluminum. 

Most of the time, it really just comes down to the project and how the metal is going to be used. Here are the best times to work with steel:

If Durability Matters

Generally speaking, steel tends to be much more durable than aluminum. It doesn’t bend or have nearly the same elasticity that aluminum has. For some projects, that’s important, especially when stability is a concern. 

If you need to make strength and durability a priority, work with steel.

Does Insulation Concern You?

Steel is a lot better at insulating heat than aluminum is. Aluminum heats up fast and has a much greater rate of heat transfer. If this is something you need to be mindful of in your project, steel might be the best choice thanks to its lower thermal conductivity.

Does It Need To Be Heavy?

Sometimes weight is an important factor, and more of it is a good thing. A piece of steel generally weighs about three times as much as a similar sized piece of aluminum. If you need to weld something where weight is a good thing, and the project needs to be heavy, steel is your best bet.

Learn More About Welding Aluminum and Steel Inside The Welder 101 Course

If you want to get really good at welding aluminum and steel or just need to refresh your current welding skills, enroll in Welder 101 today!

This welding masterclass combines 30 plus years of professional welding experience into a growing library of training resources and videos. You’ll get lifetime access to everything the course has to offer, including 50+ videos with new content being added regularly. You’ll also be able to join our private Facebook group, where you can learn and interact alongside other students and mentors.

Welder 101 students also receive great discounts on WelderUp merchandise and equipment from different manufacturers in the industry. This comprehensive course and online community are perfect for the weekend warrior who wants to improve their skills or someone looking to start a rewarding career in welding.

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