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Tips For MIG Welding Aluminum
Many welders consider welding aluminum the most challenging task due to its unique properties. Aluminum is lightweight and strong, but even the slightest mistakes can cause burn-through or surface oxidation.
Luckily, techniques and equipment have dramatically improved today, so you can tackle aluminum welding projects much more easily. Due to its ease of use and satisfying results, many new welders and beginners prefer MIG welding aluminum.
That's why we compiled tips for MIG welding aluminum, with practical advice and precautions that can help you flawlessly execute aluminum welding projects.
Should You MIG or TIG Weld Aluminum?
If you are a new or beginner welder, we recommend MIG welding aluminum due to its ease of use. MIG welding is a straightforward welding method, and with the correct set of tools and equipment, you can successfully weld aluminum.
Most seasoned welders, on the other hand, prefer TIG welding aluminum. TIG welding provides unmatched cleanliness and excellent heat control, which is crucial in aluminum welding applications. It also yields better weld aesthetics, but it has much higher skill requirements and requires more expensive equipment.
Therefore, unless you regularly weld aluminum and work on the highest-quality projects, you can get away with MIG welding. So, let's see what you need to know to successfully MIG weld aluminum.
10 MIG Welding Aluminum Tips, Tricks and Techniques
Aluminum is one of the most challenging metals to weld. The challenges arise from the surface aluminum layer that forms once bare aluminum gets in contact with oxygen. The affinity for oxygen creates a protective layer that shields the base metal from oxidation.
However, this protective layer has a much higher melting point than base aluminum. Thus, if you try welding through it, you will burn through the base aluminum.
Additionally, aluminum has high thermal conductivity. The metal dissipates the heat, which, paired with a low melting point, creates another challenge. You will need enough heat to start and maintain the arc but not too much to burn through the base metal.
So, to successfully MIG weld aluminum, you should do the following:
- Clean the aluminum
- Consider the thickness of aluminum
- Provide good wire feed
- Choose the suitable wire
- Use high-purity inert gas
- Achieve spray transfer
- Use pulsed or dual-pulsed power source
- Get a spool gun or graphene liner
- Use push technique
- Fill the crater
Let's further explain each tip.
1. Clean and prepare aluminum for welding
Aluminum is all about cleanliness, so all the surfaces must be squeaky clean before welding. Start by removing the dust, dirt, paint, or oil and grease from the surface. You can use an old rag or damp cloth, but make sure it is clean.
Next, you should remove the surface oxide layer. As noted, the oxide layer has a much higher melting point than base aluminum, so welding through it can cause many issues and burn-through. You can remove the oxides with a stainless steel brush, either a hand wire brush or a cup wire brush.
If you are using a hand brush, make sure you have a stainless steel brush you'll only use to clean aluminum pieces to avoid possible contamination. When using power tools, keep the RPMs and pressure low to reduce smearing the surface and causing contamination or oxidation.
After brushing the metal, you can wipe the surface with acetone or isopropyl alcohol. These substances will also remove some of the remaining oxides and impurities.
Keep in mind that aluminum has an affinity for oxygen, meaning it will reform the oxide layer if exposed for too long. Therefore, you shouldn't wait too long after cleaning. Align and tightly fit the pieces to be completely flush, and start welding.
2. Know the thickness limits
Aluminum comes in sheets and plates, including different thicknesses and gauges. However, for home or DIY projects, you are likely to use aluminum sheets up to 1/4 inch thick. MIG welding is suitable for most thin and medium-thickness aluminum sheets.
Conversely, seasoned welders do not recommend using MIG to weld aluminum thinner than 14 gauge (.074 inch). To weld super-thin aluminum sheets, you should consider TIG welding, which provides better heat control and stability at low amps. Additionally, consider using a pulsed MIG welder to control the heat.
Welding thick, industrial-grade aluminum requires specialized high-amp welders. But if you need to MIG weld thick sections of aluminum at home, you can preheat the pieces at 200°F to battle the high thermal conductivity and use regular 250-amp power sources.
3. Improve the wire feed
Smooth wire feed is crucial for sound and high-quality MIG welds, but there is a catch with aluminum. Because the aluminum wire is softer than steel, it can tangle, kink, clog the liner, or cause birdnesting.
To provide smooth wire feed, you should use U-groove drive rollers and check the tension. The U-rollers have smoother lines than V-rolls, so they won't deform the wire as they feed it.
Source: https://www.youtube.com/watch?v=YzMNIsdNj48&t=1794s
Tension also plays an essential role in aluminum wire feed. The overall tension shouldn't be too low to let the wire unspool itself from the main drum, and it shouldn't be too high, as it will cause birdnesting. The wire feeding mechanism will try to push the wire through to the contact tip even if there is an obstruction.
Keep in mind that softer aluminum wire can clog the MIG gun and contact tip even though you have the correct tension or rollers. To deal with this issue, you should shorten the path between the spool and the gun or use a sturdier liner. We will talk about these two solutions further in the text.
4. Choose the correct aluminum wire
Nearly 80% of all aluminum wire fillers sold worldwide are either ER4043 or ER5356. So, when MIG welding, you are likely to use one of these two types, but there are some differences you should know before making a choice.
ER4043 is a general-purpose aluminum MIG welding wire with silicon additions that lower the melting temperature and boost weld pool fluidity. Overall, ER4043 is easier to use and provides a better appearance than 5356. You can use it in most groove weld applications and with alloys that don't have high magnesium additions (5083, 5056, 5454, or most 5xxx aluminum alloys).
ER5356/1LB-0.8 1LB Spool .030" Magnesium Aluminum MIG Welding Wire
ER5356 is another general-purpose aluminum wire, but it is stronger and more rigid than ER4043. It has magnesium additives for improved tensile strength and sheer strength, which makes it suitable for high-magnesium alloys (5xxx series) and fillet welds subjected to load and stress. Since 5356 is more rigid, it is easier to feed, but it yields a worse weld appearance than 4043.
5. Use pure inert shielding gas
Base aluminum reacts with oxygen in the atmosphere to create aluminum oxide. Therefore, to protect the weld puddle from contamination, you will need high-purity, non-reactive (inert) shielding gas.
When MIG welding aluminum, always use 100% Argon shielding gas. Although MIG welding works well with CO2 mixtures or even pure CO2 as a shielding gas, you should never use CO2 in any percentage when welding aluminum. Even small doses of carbon dioxide can react with the molten puddle, cause contamination, and affect the corrosion resistance of the aluminum.
Gas flow rates of 20-30 CFH are suitable for most MIG welding applications. Use 20 cubic feet per hour if there is no draft or wind in the shop or garage, or increase it if there is a risk of poor coverage. Don't use too high gas flow, as it can create turbulence that sucks in the oxygen and cause contamination.
6. Use spray transfer mode
In MIG welding, the transfer mode denotes the way molten MIG wire is transferred across the arc and into the weld joint. There are four MIG transfer modes: short circuit, globular, spray, and pulsed transfer modes, with each running hotter (at higher amps and voltage).
Source: https://www.aedmetals.com/news/mig-welding-transfer-methods
To MIG weld aluminum, you should use the spray transfer mode or pulsed MIG. In spray transfer, the many tiny droplets with a diameter smaller than the welding wire are sprayed across the arc.
To achieve this transfer mode, you will need high current (wire feed speed or amperage) and high voltage. The high current breaks the wire into tiny droplets, and high voltage precisely sprays them into the weld joint.
Spray transfer is smooth, provides high efficiency and deposition rates, and works very well with aluminum. However, it requires high wire feed speed and voltage, so you shouldn't use it on aluminum thinner than 14 ga.
7. Consider pulsed or dual-pulsed power source
Once the aluminum gets thinner than 14 ga, you have two alternatives. Either go for AC TIG aluminum welding, which provides excellent heat control for thin aluminum or opt for a pulsed MIG power source. If you are an absolute beginner, we surely recommend pulsed MIG, as it is much easier to perform than AC TIG.
Pulsed MIG is a relatively new technology that provides better heat control, which is essential when welding delicate metals such as aluminum. In the pulsed MIG, the current oscillates between the peak amps and background amps.
During the peak amps, the current is high enough to pinch the droplets of molten wire and transfer them across the arc. During the background amps, the current is lower, so metal transfer does not occur, but the arc remains forth. This low current reduces the overall heat input into the Heat Affected Zone (HAZ), reducing the risk of burn-through, warping, or distortion of thin aluminum sheets.
Due to its advantages, the pulsed MIG is an excellent feature for aluminum welding and a must-have for thin and delicate aluminum welding. But it doesn't stop there. New welding machines include the dual-pulse feature.
In the dual pulse, another pulse is added to the primary pulse. The primary pulse switches the current from peak to background amps, while the secondary pulse turns the first pulse on and off. This feature provides even better heat control on thin and delicate aluminum and allows you to acquire that stacked dimes weld appearance.
As a result, your MIG welder can produce TIG-like welds on aluminum. If you don't want to spend a lot of money on these features, make sure you check out YesWelder DP200 Dual Pulse Aluminum MIG Welder.
Firstess DP200 Multi-Process DualPulse™ MIG Welder
8. Spool gun and graphene liner
In the wire feeding section of the article, we discussed a spool gun, push/pull gun, and graphene liner, but there is much more to discuss these two. Due to wire feeding issues with regular MIG welding equipment, a spool gun, or push/pull gun as many call it, became a must-have aluminum MIG welding equipment.
LBT150 150AMP Aluminum Welding Spool Gun
Unlike a regular MIG gun, the spool gun has its drive motor and spool hub. You mount the aluminum wire spool directly into the torch to reduce the path wire crosses from the spool to the weld and, therefore, reduce the risks of tangling or bird-nesting.
The short path and high feeding speed made the spool gun essential in any aluminum MIG welding. YesWelder MIG205 DS is a spool gun-compatible welder, so you can plug it in and weld aluminum with ease.
MIG-205DS-Pro Multi-Process MIG Aluminum Welder
If you are looking for a cheaper alternative to solving aluminum wire feeding issues, consider getting a graphene liner. The liner is a tube that guides the wire from the welder through leads and into the MIG gun tip. Its slick surface allows the softer aluminum filler metal to pass through without catching or kinking.
Graphene Aluminum MIG WeldingWire Feed Liner
Although a graphene liner doesn't provide the same feeding properties as a spool gun, it is significantly cheaper. In addition, most spool guns are limited to 1 lb spools, but with liner, you can feed the heaviest supported spools by your welder.
9. Push the gun and practice the technique
Pushing or pulling in MIG welding is a matter of preference, but most welders prefer to push. When it comes to MIG welding aluminum, push is almost always the better option.
Pushing the gun when MIG welding aluminum improves the shielding gas coverage. In MIG, you don't get the cleaning action that AC-TIG provides. Pushing directs the Argon shielding into the leading edge of the weld puddle, providing overall better shielding gas coverage and protection.
If you pull the torch, your shielding gas coverage lags. Since aluminum readily picks up oxygen, you'll see porosity and contamination quickly.
Remember that spray transfer in MIG welding aluminum means you will be running hot and fast. To avoid the burn-through, increase the travel speed, especially on thin pieces. Avoid long, continuous welds when welding thin aluminum. Prolonged heat exposure on sheets can cause distortion and warping.
Use a 3/4" wire stick stickout when welding in spray transfer. A shorter stickout can burn your tip, and you can also recess the contact tip to avoid prolonged heat exposure and damage.
10. Fill the crater
The crater is a welding defect that appears once you prematurely finish the weld without letting the weld puddle appropriately fill the end of the joint. In MIG aluminum welding, the crater is extra susceptible to thermal shock and cold cracks.
Source: https://its-good-to-be-me.blogspot.com/2011/08/weld-stops-starts.html
To address this issue, we recommend a MIG welder with a crater fill feature, such as the YesWelder DP200 Aluminum MIG welder. This feature reduces the end amps, allowing you to spend more time at the end of the weld.
The more time spent in the end, the more you will adequately fill the joint. Meanwhile, the lower amps will keep the puddle going without burning through the hole in your weld.
You can also fill the crater manually, but it requires a lot more skill than automated settings. One way to deal with this issue is to use the back-step method. In this method, you go back a few millimeters at the end of the weld to fill the puddle.
The other option is to use run-on and run-off plates. You attach the plates at the start and end of the joint. You start by welding from the run-on plate into the joint and onto the run-off plate. That way, you reduce the risk of a cold start and crater at the beginning and end of the weld.
Final Thoughts
Welding aluminum, indeed, is one of the most challenging tasks for most welders. However, you can make it a lot easier by turning to the semi-automated principle of MIG welding.
MIG welding aluminum is a straightforward way to weld aluminum for your home projects, but it still requires a lot of attention. To successfully MIG weld aluminum, make sure surfaces, environment, and fillers are clean.
Use equipment labeled or advertised for aluminum welding, such as U-groove rolls, aluminum wire, spool gun, etc. Finally, work on your technique. By combining preparation, equipment, and technique, you can successfully MIG weld aluminum every time.
🧐Tips For MIG Welding Aluminum FAQ
1. How to Clean Aluminum Before Welding？
Proper cleaning is essential to prevent issues like burn-through and oxidation. Follow these steps for a cleaner, stronger weld:
- Remove dirt and grease: Wipe the surface with a clean rag or damp cloth.
- Remove oxide layer: Use a stainless steel brush (hand or cup wire brush) to scrub the surface.
- Final wipe: Clean with acetone or isopropyl alcohol to remove any remaining impurities.
- Welding tip: Don’t wait too long to weld, as aluminum quickly forms a new oxide layer.
2. How to ensure smooth wire feed when MIG welding aluminum?
To achieve smooth wire feed with aluminum, use U-groove drive rollers, which prevent deformation of the softer aluminum wire. Ensure the tension is set correctly—too low and the wire may unspool, too high and it could cause birdnesting. Additionally, check the liner for clogs, and consider shortening the path between the spool and the gun or using a sturdier liner to prevent obstructions.
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