Aluminium differs from other metals in several keyways that impact the welding process. Its high thermal conductivity means it dissipates heat quickly, which can make it harder to maintain the weld pool and can lead to burn-through if not managed carefully. Additionally, aluminium forms a thin oxide layer on its surface, which has a much higher melting point than the aluminium itself. This oxide layer needs to be properly addressed to achieve a clean, solid weld.

Step 1: Preparing Your Workspace and Equipment

A clean, well-organized workspace is essential for successful aluminium TIG welding. Here’s how to get started:

• Welding Machine Setup: Use an AC (alternating current) setting on your TIG welding machine, as this is specifically suited for aluminium. The AC current helps break through the oxide layer while providing the necessary heat to weld the aluminium effectively.
• Choosing the Right Tungsten Electrode: For aluminium TIG welding, a 2% lanthanated or pure tungsten electrode is commonly recommended. Sharpen the electrode to a point, but leave a small, rounded tip to help stabilize the arc in AC mode.
• Selecting the Filler Rod: Use an appropriate filler rod based on the type of aluminium you’re working with. ER4043 and ER5356 are popular choices, with ER4043 offering good flow and forgiveness, while ER5356 provides higher strength and better corrosion resistance.

Step 2: Cleaning the Aluminium

Proper surface preparation is critical to achieving a strong, clean weld. The oxide layer on aluminium can cause contamination if not removed.

• Mechanical Cleaning: Use a stainless-steel brush dedicated solely to aluminium to remove the oxide layer from the surface. Brush in one direction to avoid embedding contaminants into the metal.
• Chemical Cleaning: For more thorough cleaning, wipe down the surface with acetone to remove any oils or grease that might interfere with the welding process.

Step 3: Setting Up Your Welding Parameters

Correct machine settings are crucial for controlling the arc and ensuring a smooth weld.

• Amperage: Set the amperage based on the thickness of the aluminium. A general guideline is 1 amp per 0.001 inch of material thickness. For example, for 1/8-inch-thick aluminium, set the machine to around 125 amps.
• Balance Control: Adjust the balance control to fine-tune the cleaning action of the arc. A setting of 60-70% electrode negative (EN) is a good starting point, allowing the arc to clean the oxide layer while penetrating the base metal effectively.
• Frequency: Set the AC frequency between 100-200 Hz. A higher frequency produces a more focused arc, which is useful for controlling the weld bead and working with thinner materials.

Step 4: Welding Technique and Execution

Executing the weld requires a steady hand and careful attention to detail.

• Torch Angle and Positioning: Hold the torch at a slight angle (about 10-15 degrees) relative to the workpiece. This angle helps direct the heat more effectively and provides better control of the weld pool.
• Controlling the Heat: Aluminium heats up quickly, so it’s important to control the heat input to avoid burn-through. Start with a lower amperage and increase it gradually as needed.
• Feeding the Filler Rod: Feed the filler rod smoothly and consistently into the leading edge of the weld pool. Keep the rod within the gas shield to prevent contamination.
• Welding Speed: Maintain a consistent speed to ensure even heat distribution and a uniform weld bead.

Moving too fast can result in poor penetration, while moving too slowly can lead to overheating and burn-through.

Step 5: Post-Weld Inspection and Finishing

After completing the weld, inspect your work for any defects such as cracks, porosity, or incomplete fusion.

• Visual Inspection: Look for a smooth, uniform bead with good penetration. Any signs of contamination, such as black soot or porosity, indicate that the cleaning or shielding was inadequate.
• Finishing: If needed, clean the weld area with a wire brush or use a finishing tool to remove any sharp edges or excess material.