MIG Welding Aluminium: Easy Tips and Tricks!

Aluminium is a versatile and widely used metal in various industries. Automotive and aerospace, as well as construction and manufacturing, all use a lot of aluminium. When it comes to joining aluminium parts, MIG welding is a popular method due to it's speed and ease. But MIG welding aluminium poses unique challenges compared to other metals. A low melting point, high thermal conductivity, and oxide layer all cause complications.

In this article, we will explore the world of MIG welding aluminium. Providing valuable insights, tips, and techniques. As well as best practices to help you master the art and achieve high-quality welds.

Understanding the Properties of Aluminium.

With a low melting point and high thermal conductivity, aluminium can be difficult to weld. The low melting point increases the chance of defects, with issues like warping, distortion and burn-through. While high thermal conductivity dissipates heat quickly, making it a challenge to retain heat in a specific area. Particularly in thicker material! Precise heat control and proper welding techniques will help to overcome some of these challenges. Increasing the heat input and slowing travel speed for example, will help to ensure proper fusion and structural integrity. Other things to consider are oxide formation and material porosity.

Selecting the Right Equipment for MIG Welding Aluminium.

You’ll need a MIG welder with specific features for welding aluminium. Things like adjustable voltage and wire feed speed will ensure precise setting control. The wire feeder will need to be smooth and reliable, so opt for a push-pull gun or spool on-gun to help achieve this. A MIG gun with a teflon liner will help to reduce friction with wire feeding. Reducing the chance of jamming and “bird-nesting”. The welding wire will need to be aluminium, specifically suited to MIG welding. It should match the alloy composition of the base metal, or be compatible with the specific aluminium alloy you are welding; these include ER4043 and ER5356 filler wires. Argon is a popular shielding gas for MIG welding aluminium, as it provides excellent coverage. Nozzles and contact tips have larger internal diameters for aluminium applications, helping to accommodate the softer wire. Thus preventing it from clogging, as well as allowing better flow of the shielding gas. Other consumables include the correct drive rolls for aluminium welding and wire size. As well as wire brushes and cleaning solvents for pre-weld preparation.

MIG Welding Aluminium Pre-Weld Preparation.

Preparing aluminium before welding is essential for removing oxidisation and other contaminants. Start by thoroughly cleaning the aluminium base metal with a wire or stainless steel brush. As this will help to remove things like oil, grease and other substances. You will need to use a specific solvent or chemical cleaner for aluminium to remove the oxide layer. Use with a brush or abrasive pad to gently scrub, making sure to rinse after, checking the oxide has all gone. Other, more advanced steps include using mechanical cleaners for professional/industrial use. As well as proper fit-up of the joint, equipment and gas checking. Always wear appropriate PPE!

Shielding Gas and Wire Selection.

The primary shielding gas used for MIG welding aluminium is pure argon or a mixture of argon and helium. These gases provide excellent coverage and protection for the weld pool, helping to prevent atmospheric contamination and minimising the formation of defects. Whether you use pure argon or an argon-helium mixture will depend on application and parameters. For appropriate mixtures, we recommend consulting welding reference charts, or seek guidance for the appropriate shielding gas mixture ratios. ER4043 is the most commonly used filler wire for MIG welding aluminium, suitable for welding aluminium alloys in the 3XXX and 6XXX series, such as 3003, 6061, and 6063. ER4043 offers good fluidity, excellent corrosion resistance, and good colour match after anodizing. ER5356 is ideal for welding aluminium alloys in the 5XXX series, such as 5052 and 5083. ER5356 provides higher tensile strength and improved crack resistance compared to ER4043. It is particularly suitable for applications that need higher strength and better performance in high-pressure environments.

Techniques for MIG Welding Aluminium.

Some common aluminium MIG welding techniques include the push/pull methods. Whereby you push, or pull, the MIG gun towards the weld pool, helping to control the heat input, thus improving fusion. Use the push technique for thinner aluminium sections, and pull for thick material. Using a tilted torch angle can help direct the heat towards the base metal, allowing for better penetration while maintaining good arc stability. Back-stepping helps manage heat build-up. The welder moves backward, against the direction of welding after depositing a short section, controlling distortion, and cutting the effects of thermal conductivity. Pulse welding alternates between high and low currents during the welding process. Helping to control heat input, reduce distortion, and improve weld quality. It is useful for welding thin aluminium sections, or when appearance is a critical factor. Weaving is where the MIG gun is moved in a controlled side-to-side motion while welding. It helps distribute heat and widen the weld bead, ensuring proper fusion. It is effective when welding wider joints, or when you need extra reinforcement.

Troubleshooting and Common Challenges.

Some common challenges that may arise while MIG welding aluminium include:

1. Burn-Through or Warping. Due to aluminium’s lower melting point and higher thermal conductivity, there is a higher risk of burn-through or warping. Especially when welding thin sections. To mitigate this issue, you can:

• Reduce the heat input by adjusting the voltage and wire feed speed.
• Use a smaller diameter filler wire to decrease heat input.
• Use a shorter welding arc length.
• Utilise tack welding or stitch welding techniques to aid heat distribution.

2. Porosity. Aluminium is susceptible to porosity, which manifests as gas pockets in the weld. To reduce porosity:

• Ensure the base metal is clean and free from contaminants, such as oil, grease, or moisture.
• Clean the filler wire with a stainless steel wire brush or wipe it with a clean cloth before welding.
• Use a high-purity shielding gas, such as pure argon. Along with proper flow rates to provide adequate protection.
• Adjust the shielding gas flow rate and positioning of the gas nozzle. This helps to ensure optimal gas coverage over the weld area.

3. Incomplete Fusion or Lack of Penetration. Insufficient fusion or penetration can weaken the weld joint. To address this:

• Increase the heat input by adjusting the voltage, wire feed speed, or using a higher amperage setting.
• Ensure proper fit-up and joint preparation to allow for enough penetration.
• Use weaving techniques to ensure thorough fusion across the joint.
• Consider preheating the base metal to improve weld penetration in thicker sections.

4. Oxide Formation and Contamination. The oxide layer on aluminium surfaces can hinder proper fusion and lead to weld defects. To mitigate oxide-related issues:

• Clean the base metal properly using a wire or stainless steel brush. Appropriate cleaning agents will also help to remove oxide, dirt, and contaminants.
• Use a dedicated stainless steel wire brush for aluminium to prevent cross-contamination.
• Use mechanical cleaning methods like abrasive pads or sanding, for tougher oxide layers.
• Consider using a suitable aluminium-specific cleaning agent to remove oxide effectively.

5. Wire Feeding Issues. Aluminium wire can be softer and more prone to tangling or bird-nesting in the wire feeder. To address this:

• Use a spool gun setup or a push-pull wire feeding system to ensure smoother wire feeding.
• Maintain proper tension on the wire spool and drive rolls to prevent wire slippage.
• Check the contact tip size and condition to ensure it matches the wire diameter. It should also be clean and free from debris.

6. Joint Fit-Up and Alignment. Poor joint fit-up and misalignment can lead to weld defects and compromised strength. Consider the below:

• Ensure accurate joint fit-up and alignment before welding.
• Use clamps or fixtures to hold the parts securely in position during welding.
• Use appropriate joint preparation techniques, such as bevelling or grooving. Ideal for thicker sections or critical applications.

Practice and experimentation with welding parameters is key. Experience will help you troubleshoot specific challenges encountered during aluminium MIG welding. We recommend consulting welding references, as well as seeking guidance from experienced welders. Also conduct test welds to optimise your technique and achieve high-quality aluminium welds.

MIG Welding Aluminium Safety and Health Considerations.

As well as general welding safety, you should consider some aluminium-related hazards too. Aluminium is a good conductor of electricity, so be aware of the potential for electrostatic discharge. Take precautions to prevent accidental contact with electrical components, as well as grounding yourself and the workpiece to avoid static build-up. Aluminium welding involves high heat and sparks, increasing the risk of fire hazards. Make sure there are fire extinguishers nearby, and clear the workplace of flammable material like card and paper. Any flammable items that can’t be moved should be covered in a fireproof blanket or use a welding curtain. Take caution around hot workpieces and spatter, as these can ignite flammable material. Standard welding practices like appropriate PPE and eyewear, as well as proper ventilation with a fume extraction filter, should all be employed when welding aluminium. Ensure you have had adequate training on the process and safety aspects, and finally, familiarise yourself with the equipment and it’s operating manuals for success!