When welding any type of metal, you want the best tools for the job. Aluminum’s chemical characteristics make some types of welding more effective than others. So, when working with aluminum, which is notoriously tricky to weld, you definitely want the ideal type of welder to get the job done correctly on the first try.
The best and most effective welder for welding aluminum is TIG welding. The current control allows you to weld both aluminum sheets and plates. MIG welders can also be used to weld thinner aluminum, with some preparation and special care taken to ensure your success.
While welding aluminum is tricky and sometimes challenging, it’s doable. Depending on the type of aluminum you’re working with and your specific needs as a welder, you may need different types of welders to achieve your desired result. In this article, we’ll be discussing some of the characteristics of aluminum, why it isn’t easy to weld, and why some welders work better than others.
Aluminum vs. Steel
Steel and its alloys are some of the most common materials people work with when welding, so it can help compare and contrast it to aluminum to help people get a better understanding.
First of all, steel has a melting point over twice that of aluminum. The melting points of steel and aluminum are 2,500 °F (1,370 °C) and 1,221 °F (660.3 °C), respectively. That in mind, combined with the fact that steel and aluminum behave very differently when exposed to heat, makes transitioning from steel welding to aluminum much harder.
When you weld steel, it has certain stages that indicate where you are in your process and when you can advance with the welding. First, it changes color, then glows, and then melts. On the other end of the spectrum, aluminum has few indicators that tell you where you are with it – it simply glows and gets shinier!
Welding, like many life and career skills, is an ongoing educational process. Aluminum might seem difficult to learn, but as you practice, you’ll learn how to spot its visual indicators and weld it as easily as steel.
Why Is Aluminum Hard To Work With?
Aluminum might be pretty and light, which are appealing, but due to its very nature, it’s very tricky to learn how to weld. With time, practice, patience, and perhaps a teacher, it isn’t that difficult. There are several specific characteristics of aluminum that make it necessary to change your welding approach.
Low Melting Point
Due to aluminum’s comparatively low melting point, it can be easy just to see the metal going shiny and getting hotter, and then all of a sudden, it’s burned! When aluminum is molten, it’s highly susceptible to impurities getting in and ruining your weld, making it weak and porous. Try practicing different techniques when heating aluminum, depending on your welder, to see what works best for you.
Oxidation
Aluminum is usually a very soft metal sandwiched by an outside layer of oxidized metal. This outer layer is due to a reaction with aluminum and the air. It is extremely thin – only a few nanometers.
Although aluminum itself has a low melting point, that outside layer, aluminum oxide, has a melting point as high as steel. See the problem? Getting through the aluminum oxide to the metal beneath takes high heat, but that same heat can quickly burn holes in the aluminum. Because of this, aluminum usually only gives you a small window it can be worked with unless the oxidized layer is removed.
Sensitive To Impurities
Pure aluminum is a very touchy metal when welding because any number of impurities can cause your weld to be compromised. Ideally, you want to weld aluminum immediately after cleaning off the oxidized layer. Otherwise, you risk impurities contaminating the metal. If you can’t immediately weld it, you have to store it in a clean and secure place to keep air, dirt, and other materials off it.
High Thermal Conductivity
Like copper, aluminum has excellent thermal conductivity, which means it naturally disperses heat at a high rate. This is desirable in some of its applications but makes welding it a pain. Simply put, when you start welding, the beginning doesn’t achieve penetration because the heat initially disperses, but the end does penetrate – this is known as a cold start. It would be best if you always endeavored to prevent them when working with aluminum.
Porousness
Molten aluminum takes in a lot of hydrogen at an alarming rate. When that hydrogen separates out from the metal, it causes bubbles and pinholes in your weld that essentially destroy its integrity. Using the proper shielding gas will prevent this from occurring.
With steel, hydrogen causes cracking, but that doesn’t happen in aluminum. However, aluminum can still suffer from hot cracking, sabotaging your hard work and effort. To minimize hot cracking in your aluminum weld.
Thickness
Aluminum thickness varies wildly, from thin sheets to thick plating. Regardless of the thickness, you need to know how to apply the right amount of heat to penetrate an oxidated layer without ruining the underlying metal. Without visual indicators to go by, it can be easy to think you’ve achieved penetration and created a strong weld when, in fact, you haven’t. Even worse, you may burn and ruin the metal altogether.
TIG Welding
Tungsten inert gas welding, or TIG welding, is the primary method employed by most welders in the majority of cases dealing with aluminum. Aluminum takes a lot of heat to heat up. It holds it for a long time, making current control useful to prevent the metal from overheating and burning.
TIG is incredibly useful for aluminum in particular because the alternating current essentially ‘cleans’ or removes the outer oxidized layer that can save you a lot of pain and frustration.
TIG is often used for aluminum because it applies to both thin aluminum sheeting and thick aluminum plates, reducing the need to switch equipment. Due to TIG welding’s need for a filler rod, you should make sure you get one that’s the closest thing possible to the alloy you’re welding.
MIG Welding
Metal inert gas welding, or MIG welding, is also usable with aluminum with some caveats. Because of the amount of heat involved, MIG is better for working with thin aluminum. When pulse welding, you’ll need an inverter power supply. In contrast, spray arc welding requires a constant current and constant wattage machine.
As far as welding wire or rods, you’ll want the closest thing to the alloy you’re welding. 100% argon should be used as the shielding gas when welding aluminum.
A note about shielding gas that applies to both TIG and MIG welding with aluminum is that both argon and helium can be used. Argon is ideal because helium requires higher voltage because of its ionization potential.
Torch Method
It’s technically possible to weld aluminum with a torch. Still, it’s not recommended for beginners because of the amount of dexterity and familiarity with welding aluminum necessary to make it an effective method. If done incorrectly, using a torch to weld aluminum will just burn up the metal.
Final Thoughts
Welding aluminum can be difficult to learn because of aluminum’s unique characteristics, but that doesn’t mean it can’t be learned. With the right type of welder (TIG or MIG, preferably) and a lot of practice and patience, you can weld aluminum like a pro in no time.