The best shielding gas for aluminum MIG welding is 100% argon. Argon is preferred due to its excellent arc stability, cleaning action, and penetration characteristics, which are crucial for welding aluminum. It provides a smooth, stable arc and helps in achieving a clean weld with minimal spatter. Argon also facilitates good bead appearance and reduces the risk of porosity, which is a common issue when welding aluminum. In some cases, a small percentage of helium (usually 25% to 75%) can be mixed with argon to increase heat input, which is beneficial for welding thicker aluminum sections. The addition of helium enhances the fluidity of the weld pool and increases penetration, but it can also make the arc more difficult to control and increase the cost of the shielding gas. For most applications, especially when welding thinner aluminum materials, pure argon is sufficient and provides the best balance of performance and cost-effectiveness.

The best size MIG wire for welding aluminum typically ranges from 0.030 inches (0.8 mm) to 0.047 inches (1.2 mm), with 0.035 inches (0.9 mm) being the most commonly used size for general applications. The choice of wire size depends on several factors, including the thickness of the aluminum being welded, the welding position, and the specific requirements of the project. For thinner aluminum materials, such as those less than 1/8 inch (3.2 mm) thick, a smaller wire size like 0.030 inches is often preferred. This size allows for better control and reduces the risk of burn-through. For thicker materials, a larger wire size, such as 0.035 inches or 0.047 inches, is more suitable as it provides better penetration and a stronger weld. Additionally, the welding position can influence the choice of wire size. For instance, when welding in a vertical or overhead position, a smaller wire size may be easier to control and produce better results. It's also important to consider the type of aluminum alloy being welded, as different alloys may have varying requirements. The use of a spool gun or a push-pull system is recommended for feeding aluminum wire, as aluminum is softer and more prone to feeding issues compared to steel. Ultimately, the best wire size is determined by balancing these factors to achieve optimal weld quality and efficiency.

To prevent burn-through when MIG welding aluminum, follow these steps: 1. **Material Thickness**: Choose the appropriate material thickness. Thicker aluminum is less prone to burn-through. For thin materials, consider using a backing bar to absorb excess heat. 2. **Welding Technique**: Use a push technique rather than a pull technique. This helps in better heat distribution and reduces the risk of burn-through. 3. **Wire Feed Speed and Voltage**: Adjust the wire feed speed and voltage settings on the welder. Lower settings can help prevent excessive heat input, reducing the risk of burn-through. 4. **Travel Speed**: Increase the travel speed to minimize the heat input into the material. Faster travel speeds help in reducing the time the heat is applied to any one spot. 5. **Shielding Gas**: Use 100% argon as the shielding gas. It provides better arc stability and reduces the risk of burn-through compared to mixed gases. 6. **Nozzle Distance**: Maintain an appropriate distance between the nozzle and the workpiece. A distance that is too close can concentrate heat, while too far can lead to poor shielding. 7. **Pre-Weld Preparation**: Clean the aluminum surface thoroughly to remove any oxides or contaminants. This ensures better conductivity and reduces the risk of burn-through. 8. **Pulse Welding**: If available, use a pulsed MIG welding process. Pulsing allows for better control over heat input, reducing the risk of burn-through. 9. **Practice and Experience**: Gain experience by practicing on scrap pieces of aluminum. This helps in understanding the heat input and adjusting techniques accordingly. 10. **Joint Design**: Consider joint design modifications, such as using a lap joint instead of a butt joint, to distribute heat more effectively and reduce the risk of burn-through.

For aluminum MIG welding, the recommended voltage and amperage settings depend on the thickness of the material and the specific welding application. Generally, aluminum requires higher voltage and amperage settings compared to steel due to its high thermal conductivity and lower melting point. Here are some general guidelines: 1. **Material Thickness**: - **1/16 inch (1.6 mm)**: Use approximately 17-19 volts and 80-100 amps. - **1/8 inch (3.2 mm)**: Use approximately 18-21 volts and 100-130 amps. - **3/16 inch (4.8 mm)**: Use approximately 20-23 volts and 130-170 amps. - **1/4 inch (6.4 mm)**: Use approximately 21-24 volts and 170-220 amps. - **3/8 inch (9.5 mm)**: Use approximately 22-25 volts and 220-280 amps. 2. **Wire Feed Speed**: - Adjust the wire feed speed to match the amperage setting. Higher amperage requires a faster wire feed speed. For example, a 1/16 inch thickness might require a wire feed speed of 300-400 inches per minute (IPM), while a 1/4 inch thickness might require 400-600 IPM. 3. **Shielding Gas**: - Use 100% Argon as the shielding gas for aluminum MIG welding to ensure proper arc stability and weld quality. 4. **Welding Technique**: - Use a push technique to ensure better gas coverage and minimize contamination. - Maintain a short stick-out distance to prevent burn-back and ensure a stable arc. These settings are starting points and may need adjustments based on specific welding conditions, equipment, and personal technique. Always refer to the welding machine's manual and perform test welds to fine-tune the settings for optimal results.

To avoid wire feeding issues when MIG welding aluminum, ensure the following: 1. **Use the Right Equipment**: Opt for a spool gun or a push-pull system to minimize feeding problems. These systems are designed to handle the softer aluminum wire more effectively than standard MIG setups. 2. **Select Proper Wire**: Use aluminum wire specifically designed for MIG welding, typically 4043 or 5356 alloys, depending on the application. Ensure the wire diameter is appropriate for the welding task. 3. **Adjust Tension Correctly**: Set the drive roll tension just enough to push the wire without crushing it. Aluminum wire is softer and can easily deform, leading to feeding issues. 4. **Choose Correct Drive Rolls**: Use U-groove drive rolls instead of V-groove or knurled rolls. U-groove rolls provide better grip without deforming the wire. 5. **Maintain Cleanliness**: Keep the wire and liner clean. Dust, dirt, or debris can cause feeding problems. Regularly clean the liner and replace it if necessary. 6. **Use a Teflon or Nylon Liner**: These liners reduce friction and are gentler on the soft aluminum wire, helping to prevent kinks and jams. 7. **Optimize Feed Speed and Voltage**: Set the wire feed speed and voltage according to the manufacturer's recommendations for aluminum. Incorrect settings can lead to burn-back or bird-nesting. 8. **Check for Kinks and Bends**: Ensure the welding cable is as straight as possible to prevent resistance and feeding issues. Avoid sharp bends and kinks. 9. **Regular Maintenance**: Regularly inspect and maintain all components of the wire feed system to ensure smooth operation. 10. **Preheat the Material**: Preheating can help reduce the wire feed speed required, minimizing feeding issues. By following these guidelines, you can significantly reduce wire feeding issues when MIG welding aluminum.