MIG Welding Aluminum for Beginners - Tips and Techniques
Dec 15, 2023
If you're looking to get started with MIG welding aluminum, you're in the right place. Welding aluminum is notoriously difficult, but with the right knowledge and techniques, you can create quality welds.
Compared to TIG welding, MIG welding aluminum is easier and requires less expensive equipment. However, there are still many variables and potential pitfalls to be aware of.
In this guide, we'll cover the basics of MIG welding aluminum for beginners, from why aluminum is challenging to weld to how to set up your MIG welder, clean the aluminum, and use basic welding techniques. Let's dive in and get started on your journey to mastering MIG welding aluminum.
Why Welding Aluminum Is Difficult
Welding aluminum is a challenging process because of its unique properties. Aluminum has a great affinity for oxygen, and as a result, its atoms combine with oxygen from the air forming an oxide layer on the aluminum's surface. This oxide has a higher melting point than the pure aluminum underneath it, and this is the first challenge you'll face when welding aluminum. In a nutshell, this means that you must remove the oxide layer before attempting to MIG weld aluminum.
Pure aluminum has a melting point of 1200°F (650°C) while the oxide on the surface has a melting point of 3700°F (2037°C). This means that you need to apply more heat to weld this metal compared to mild steel. However, the low melting point of pure aluminum, coupled with the need to apply high heat due to aluminum's high conductivity, results in a narrow window of temperature workability. This means it's easy to burn through or not apply enough heat to start the puddle.
Aluminum has a strong proclivity for contamination. Therefore, it must be thoroughly cleaned and welded in a relatively clean environment. Be careful of cross-contamination resulting from airborne metal dust particles like mild steel dust and sparks. Additionally, the aluminum welds will shrink in volume by approximately 6 percent after the weld cools. The shrinkage may lead to cracks due to excessive joint distortion from the resulting stresses.
The high conductivity of aluminum is another challenge that you'll face when welding aluminum. Aluminum rapidly conducts the heat away from the welded joint, making it difficult to maintain the temperature required for welding. This may result in porosity and other welding defects. The welding process must be carefully controlled to ensure that the heat input is sufficient to melt the aluminum, but not so high that it causes burn-through or distortion.
In summary, welding aluminum is difficult due to the unique challenges posed by the metal's properties. The high conductivity of aluminum, low melting point, and oxide layer formation make it challenging to weld. Additionally, the metal's strong proclivity for contamination and shrinkage after cooling further compound the difficulties of welding aluminum.
Cleaning the Aluminum Before MIG Welding
Before beginning the MIG welding process on aluminum, it is essential to clean the metal thoroughly. The presence of dirt, oils, and grease on the surface of the aluminum can embed impurities into the metal when the oxide layer is removed. To avoid this, it is necessary to clean the aluminum surface with a wire brush dedicated to aluminum only. Using a brush that was previously used to clean mild or stainless steel can contaminate the aluminum, resulting in weak welds due to porosity.
In addition to using a wire brush, specialized grinding wheels for aluminum can also be used to remove the surface oxide. However, regular grinding wheels are not recommended as they can quickly load up with aluminum due to its softness and low melting point. Strong alkaline or acid can also be used to clean the aluminum, but it must be rinsed and thoroughly dried before welding.
It is important to note that the naturally occurring oxide layer on the aluminum surface must be removed before welding. However, removing this layer first is not recommended. Instead, it is recommended to clean the aluminum surface first to avoid dirty welds. Once the surface is cleaned, the oxide layer can be removed using a stainless wire brush or a cup wire brush. Acetone can also be used to remove the oxidized layer.
Safety Tip: Aluminum is a non-magnetic metal, and if dust or debris enters your eyes, ophthalmologists will have a difficult time providing medical care. Therefore, it is essential to wear all necessary safety equipment, including eye protection, when cleaning and welding aluminum.
In summary, cleaning the aluminum surface before MIG welding is crucial to avoid embedding impurities into the metal. Use a wire brush dedicated to aluminum only, and avoid using regular grinding wheels. Once the surface is cleaned, the oxide layer can be removed using a stainless wire brush or a cup wire brush. Remember to wear all necessary safety equipment, including eye protection, to avoid any accidents.
Safety Equipment For MIG Welding Aluminum
When MIG welding aluminum, it is crucial to prioritize safety by using the appropriate equipment. Here are the essential safety gear to consider:
- ArcCaptain Welding Helmet: Protects your eyes and face from harmful radiation.
- Welding Gloves: Shields your hands from high heat and molten spatter.
- Welding Jacket and Apron: Provides additional protection against radiation and heat.
- Welding Respirator: Recommended, especially in poorly ventilated environments.
- Safety Glasses: Should be worn underneath the welding helmet, especially during grinding or cutting activities.
Always adhere to the safety codes and regulations in your area, as welding can be a hazardous activity if proper precautions are not taken.
Preparing Your Equipment to MIG Weld Aluminum
Before you start MIG welding aluminum, you must ensure that you have the right equipment and settings. Here are some essential aspects to consider:
MIG welding aluminum requires the use of 100% Argon shielding gas in most cases. Pure argon is the most popular shielding gas because it allows great arc start and stability. Adding helium helps with penetration but at the cost of arc stability and widens the weld bead. So, for most people, pure argon shielding gas is the way to go.
MIG Welding Aluminum Wire Selection
Aluminum welding filler wire selection depends on base aluminum alloy and the conditions the finished part will be subjected to. The most commonly used MIG aluminum welding wires are ER4043 and ER5356.
ER4043 is a general-purpose MIG welding wire used to weld 2014, 3003, 3004, 4043, 5052, 6061, 6062, and 6063 aluminum alloys. The welds provide high ductility and excellent resistance to cracking. Plus, the wire has silicon additions which lower the melting temperature and promote weld pool liquidity.
ER5356 has magnesium additives for improved tensile strength, but unlike the ER4043, the ER5356 has a lower resistance to cracks during welding. The ER5356 welds 5050, 5052, 5056, 5083, 5086, 5154, 5356, 5454, and 5456 aluminum alloys.
Spool Gun or Graphene Liner for a MIG Gun
Either a graphene liner set up or a ArcCaptain spool gun is necessary to MIG weld aluminum. That's because the aluminum wire is soft and can easily kink in the regular wire feed meant for mild steel wire. You can successfully MIG weld aluminum without a spool gun if you use a graphene liner for a MIG gun and a few other parts the MIG welder manufacturer may specify.
A spool gun is also an option, but it's an additional investment. The spool gun has a spool system attached to the MIG gun and a wire feed drive roll. So the aluminum wire doesn't have to travel from the wire spool inside the welder and possibly cause wire nesting. The advantage of a spool gun is the improved reliability. Still, the disadvantage is higher costs and the inability to access tight spaces because of the large spool attached to it.
Achieving a Spray Transfer When MIG Welding Aluminum
When MIG welding aluminum, it's best to achieve a spray transfer. Spray transfer requires high travel and wire feed speeds. It uses high amperage and voltage settings and results in tiny molten droplets across the arc. The arc stays ignited at all times, and the metal deposition rate is high. The wire use efficiency is also higher than globular or short circuit because there is very little filler metal lost through spatter.
To achieve spray transfer for MIG welding aluminum, you need to set up the wire feed speed and voltage to work together. Not one should be too low or too high in comparison to another. It's best to use the MIG welder's recommended settings and fine-tune them for your personal preference.
You should know as a beginner that if you need to increase the wire speed and voltage to weld thicker sections, you should proportionally increase both settings. Additionally, it's better to start with the lower voltage than overly high voltage settings because your MIG gun tip can arc out and need replacement. Then, gradually increase the voltage on the test aluminum piece until you get a feel for it.
On the other hand, if you are running too hot and burning through the aluminum, lower the wire feed speed and voltage but again with the emphasis on testing out the lower voltages first. Once you get better at this, you won't need to make test welds.
Preheating the Aluminum
In a professional setting, preheating aluminum is not usually necessary. However, preheating can be beneficial for light welding shops or hobbyist applications. Preheating with a standard rosebud to approximately 200°F can help weld thicker material and larger aluminum sections.
Due to aluminum's high conductivity, it can be challenging to weld thicker parts with standard equipment. In professional environments, high amperage equipment is used to weld thicker aluminum, and preheating is not required. However, most people do not have access to industrial-level welders or need to weld thicker aluminum, so preheating can be helpful.
It's crucial to never preheat above 200°F because the aluminum loses mechanical properties with too much heat exposure. Therefore, keep all preheating to a minimum and only apply it if necessary.
Here are some benefits of preheating aluminum:
- Helps weld higher material thickness and massive aluminum sections
- Makes it easier to weld thicker parts with standard equipment
- Can be useful for light welding shops or hobbyist applications
Remember to keep preheating to a minimum and only use it if necessary.
MIG Welding Aluminum Technique
When MIG welding aluminum, it is best to use the push welding technique. Pushing the MIG welding gun away from the puddle instead of pulling it results in a better cleaning action, improved shielding gas coverage, and reduced weld bead contamination. This technique is essential to achieve the best weld quality.
The temperature window is narrow between the low aluminum melting temperature and the high heat conductivity, which requires high heat input. Therefore, you need to weld hot and fast. This means using high travel speed because otherwise, you risk burn-through, especially when aluminum welding thin sheets. Additionally, as the entire aluminum piece heats up as you weld, you'll have to increase the travel speed even more.
If you need to weld slower, you can use a heat sink to absorb the excessive heat conducted away from the welding gun joint. This technique is helpful in preventing burn-through when welding thin sheets.
When MIG welding gun aluminum with a spray transfer, you will need a longer wire stick out. That's the distance between the wire tip and the metal piece. You should have about a 3/4" wire stick out in this setting. Using a shorter stick out distance tends to burn tips and makes it difficult to keep a steady spray transfer.
To prevent burning tips, keep them recessed about 1/8" inside the nozzle. Since the weld puddle and reflective heat get very hot, keeping the contact tip any closer than that increases the chance of wire burning back to it.
Moving around the part will spread out the heat, which is helpful if you wish to reduce distortion of thin aluminum pieces and melt through. So if possible, it's beneficial to break up welds into multiple stages. This technique will help spread out the heat and reduce distortion.
In conclusion, to achieve the best results when MIG welding aluminum, use the push welding technique, weld hot and fast, use a heat sink if necessary, maintain a 3/4" wire stick out when using a spray transfer, keep the contact tip recessed 1/8" inside the nozzle, and break up welds into multiple stages. These techniques will help you achieve high-quality welds with minimal burn-through and distortion.
In conclusion, MIG welding aluminum requires practice, but it is a skill that can be mastered. While it may be easier than AC TIG welding, it provides less workability and adjustability. After completing a few projects, you will feel more confident and improve your skills. However, always remember to practice welding safety, wear proper personal protective equipment, and abide by the welding machine and other equipment instructions. Welding aluminum can be as dangerous as MIG welding mild steel if necessary precautions are not implemented. Overall, with the right equipment, safety precautions, and practice, you can become proficient in MIG welding aluminum.
Frequently Asked Questions
What equipment is needed for a beginner to start MIG welding aluminum?
To start MIG welding aluminum, you will need the following equipment:
- MIG welder with aluminum spool gun
- Aluminum wire
- Shielding gas (100% Argon)
- Welding gloves
- Welding helmet
- Wire brush for cleaning
Can aluminum be MIG welded without using shielding gas?
No, aluminum cannot be MIG welded without using shielding gas. Shielding gas is necessary to protect the weld from contaminants and oxidation during the welding process.
What are the optimal settings for MIG welding aluminum?
The optimal settings for MIG welding aluminum depend on the thickness of the material being welded. Generally, a wire feed speed of 200-300 inches per minute and a voltage of 18-20 volts are recommended. It is important to adjust the settings based on the specific thickness of the aluminum being welded.
How can a standard MIG welder be adapted for aluminum welding?
A standard MIG welder can be adapted for aluminum welding by using an aluminum spool gun. The spool gun allows for direct feeding of the aluminum wire and prevents the wire from tangling or bird-nesting.
What techniques are recommended for MIG welding aluminum to achieve the best results?
To achieve the best results when MIG welding aluminum, it is recommended to use the following techniques:
- Push the gun away from you while welding
- Use a weaving motion to distribute the heat evenly
- Use a slight drag angle to prevent the gun from pushing the puddle
- Keep the gun at a 10-15 degree angle to the workpiece
How should aluminum be cleaned and prepped before MIG welding?
Before MIG welding aluminum, the workpiece should be cleaned and prepped to remove any contaminants or oxidation. This can be done by using a wire brush or grinder to remove any surface impurities. It is also recommended to use a solvent or degreaser to clean the surface of the aluminum.