Welding with aluminum can present challenges to even the most experienced welders. While it is a common type of metal used in fabrications shops worldwide, learning how to weld aluminum takes time and practice. You see, aluminum is both lightweight and non-corrosive, which makes it an ideal choice for many projects. Besides just being aesthetically pleasing to the eye, this type of metal can be used for a variety of welds.
Welding aluminum is quite different from welding steel. Aluminum is a softer metal and highly sensitive. It’s protected and insulated by a strong oxidized layer. This is partly what makes welding aluminum so tricky. Pure aluminum has a melting point of around 1200°F, but the oxidized layer melts around 3700°F. To get around this, you need to make sure you clean the aluminum and remove the oxidized layer before beginning your welding operations. If you don’t, there’s a good chance you’ll end up burning through the aluminum because the area gets too hot to melt the oxidized layer.
While it takes time to master the art of welding aluminum, doing so will help you become a better welder overall and increase the number of materials and projects you can work on!
Welding With Aluminum: MIG vs. TIG
Both MIG and TIG methods can be used to weld aluminum. If you’re looking for a simple and quick weld, MIG welding tends to be the way to go. However, if accuracy, control, and less distortion are what you’re after, TIG welding is your best choice.
The vast majority of the time, TIG welding should be used when working with aluminum. With this method, you’ll have much greater control. This is especially important to help prevent the aluminum from overheating. Another benefit to TIG welding aluminum is the use of your other hand to control the filler rod. With this technique, you can avoid wire feeding issues you might encounter when using a MIG welding machine. As a result, you get a much cleaner-looking weld overall.
If you’re not comfortable with TIG welding, MIG welding aluminum does get the job done. You need to make sure that your machine is configured for only pulse welding or spray arc welding when you work with aluminum.
How to MIG Weld Aluminum
With the right equipment and technique, MIG welding aluminum isn’t as difficult as it may sound. Since this metal’s properties differ significantly from steel, you might encounter some challenges such as distortion or sensitivity to the heat.
Regardless though, following these preparation steps will help you complete strong welds when working with aluminum:
- Material Thickness
Make sure your material isn’t too thin. Ultimately, the output capacity of your welding machine will determine this. In most cases, you should be able to MIG weld aluminum as thin as 14 gauge. Anything thinner will require more specialized welding machines.
- Preparing the Materials
You need to make sure you thoroughly clean the aluminum before you begin welding. To remove the oxidized layer, make sure you use a wire brush. You can also use a powered wired brush, but you’ll need to be careful and make sure to keep the RPMs low. In either case, make sure whatever wire brush you choose is only used on aluminum. Working a brush that has been used on other types of metal could contaminate your aluminum.
- Select the Right Gas
Using the correct shielding gas is very important if you want to make strong welds. When working with aluminum, stick to 100% argon shielding gas. In most cases, you’ll want the flow rate to be somewhere around 20-30 cubic feet per hour.
- Use the Correct Filler Metal
The two most commonly used aluminum filler wires are ER4043 and ER5356. Before you start using one, though, make sure that you know what conditions the finished part of your weld will be subjected to. This will help ensure your welds will not degrade over time and maintain their strength.
Aluminum MIG Welding Technique
Once you’ve got all your preparation complete and your machine is set up to MIG weld aluminum, it’s time to get to work. As you begin to complete your welds, keep these MIG welding technique tips in mind.
- Push, don’t pull. You’ll want to make sure to use a 10-15 degree travel angle and keep the tip and nozzle pointed in the direction of travel. Using the pull method results in a lack of gas coverage and creates porous or dirty welds.
- Keep your tip-to-work distance around ¾ of an inch. If possible, the contact tip should be recessed about ⅛ of an inch inside the nozzle. Holding the nozzle too close to the weld could lead to wire burn and feeding problems.
- Increase the travel speed as your work. The aluminum will continue to heat up during the weld and could result in burn-through if your travel speed is too slow.
- Use multiple straight pass beads instead of large weave beads. This will help you avoid possible weld defects, burn-through and create an overall better and stronger-looking weld when complete.
How to TIG Weld Aluminum
TIG welding, or as it’s more formally referred to as “gas tungsten arc welding,” is the best option for welding aluminum. TIG welding uses a welding machine with an alternating current, 100% argon shielding gas, and filler rod to create strong aluminum welds.
Make Sure To Use An Alternating Current
As mentioned above, you need to clean aluminum before welding to remove the oxidized layer. The thing is, though, that oxidized layer begins to start reforming as soon as you’re done cleaning it. To get around this, make sure to use an alternating current (AC) when TIG welding aluminum. By changing the polarity to AC, the direction of the current flow alternates and changes during the weld. This provides a cleaning action to remove that oxidized layer as it reforms. This helps create better visibility of the weld pool.
Pay Attention to Your Balance Control
It’s important to monitor the balance control when welding in AC polarity. An AC waveform has two parts, the electrode-negative cycle (EN) and electrode-positive cycle (EP). If you’re using an older machine, it likely has a 50/50 ratio of EN and EP cycles. However, the more modern machines we use today come factory reset with a ratio of 75/25. The difference is that today’s machines have a balance control to adjust the ratio as needed.
For instance, if you start to see peppering (small black dots) in the weld puddle, you should lower the EN and increase the EP cycles. Doing so will help remove more oxide and help clean the aluminum as you complete the weld.
Adjust the Output Frequency
AC output frequency is how many times per second the polarity switches. Just like the balance control, you’ll find most older machines come stock with an output frequency of 60 hertz. Today’s machines are adjustable, though, and come preset with an output frequency of 120 hertz. This creates a tighter and more stable arc and gives you more directional control.
There might be times that you wish to lower the frequency to around 80 to 90 hertz. This would be the case if you were welding an outside corner joint. By reducing the output frequency, you can create a wider arc cone. Similarly, increasing the output frequency will create a tighter cone for more control when welding thinner pieces of aluminum.
Use the Correct Amperage
TIG welding machines use a foot pedal or control on the torch to adjust the amperage. Before you start welding, make sure you set the correct amperage for the thickness of the material and joint being welded. It’s recommended that you use about 1 amp for every thousandth of material thickness. If your aluminum is ⅛ inch (0.125) thick, that will require 125 amps.
As mentioned, also pay attention to the joint you’re welding. With at-joint, you have the heat flowing in three different directions. In this case, you might want to bump the amperage up a touch more to offset the additional heat input that’s needed to weld the joint.
Aluminum TIG Welding Technique
TIG welding aluminum properly takes practice. Once your machine is correctly set up as outlined above, keep these tips in mind to improve your technique.
- Pay attention to your hand and torch placement. These are crucial to having good puddle control and completing strong welds. If your hands aren’t working together and moving as one, you’ll end up wasting a lot of good materials.
- Speaking of puddle control, make sure you monitor the puddle as you travel along the weld. Aluminum acts like a heat sink and gets hotter and hotter. As this happens, your puddle may end up getting wider. To keep it consistent, you may have to ease up on the foot pedal or amperage control on the torch.
- The last piece of the puzzle is adding your filler material to the puddle. When your hands are working together as one, this is much easier. If you’re just learning this technique, start by making small dabs as you move along. Once you get into a rhythm with your hands, you’ll be able to start laying a proper bead profile.
Common Aluminum Welding Issues
Welding aluminum can be quite different than steel and other materials you may have worked with previously. Its low melting point and higher thermal conductivity result in a smaller window of workability. Here are some of the common issues amateur and professional welders encounter when they are working with aluminum.
When aluminum is in a molten state, it absorbs hydrogen quicker as it heats up more and more. As the metal returns to its solid form, the hydrogen begins to separate out. When this happens, it creates bubbles in the material. As a result, the aluminum becomes more porous and thereby weaker overall.
Be mindful of how thick or thin the aluminum is. As mentioned above, anything thinner than 14 gauge will require specialized equipment to complete strong welds. Make sure you pay attention to your machine settings and travel speed to avoid burning through the aluminum when completing a weld.
The oxidized layer that sits on the top of aluminum helps strengthen the metal. Aluminum is very soft and needs this insulating layer. While this layer is needed to maintain the strength of the metal, it also creates difficulties when it comes time to weld. Since the melting point of the oxidized layer is so much higher than pure aluminum, you need to make sure to clean and remove this before beginning any welds. Otherwise, you may find that the intense heat needed to melt the oxidized layer results in burn-through holes on the aluminum underneath.
Aluminum is a very soft and sensitive type of metal. Dirt, air, grease, and water can all create impurities and contaminate the weld. These impurities reduce aluminum’s strength and ductility. To avoid this from happening, you need to make sure to properly store and thoroughly clean your aluminum materials before any welding operations begin.
Master the Skills to Weld Aluminum
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