Choosing filler metals and shielding gas
- Shielding gas: Pure argon is the recommended gas for aluminum TIG welding. An argon/helium mix can be used when welding on thicker materials (greater than 3/8 inch) because the addition of helium creates a hotter weld puddle. Shielding gas flow should typically be set at 15 to 20 cubic feet per hour (cfh) when welding in the flat position. For out-of-position welds or when welding where there are drafts or gusts of air, you may need to adjust the flow rate to a higher setting such as 20 to 25 cfh. Avoid using too much shielding gas, as it can result in turbulence in the weld puddle that can create porosity and pinholes.
- Tungsten: For welding repairs on aluminum, 2% ceriated tungsten sharpened at the tip is a good all-purpose tungsten for AC welding, because it allows for the use of 30% more amperage compared to pure tungsten of the same diameter. Sharpened (or pointed) tungsten also offers easy arc starts and a narrower heat-affected zone, along with the ability to control penetration more accurately. A 3/32-inch diameter tungsten is adequate for most repairs, but an 1/8-inch diameter tungsten should be used on 3/8-inch or thicker aluminum. Not surprisingly, tungsten preparation and cleanliness are just as important as joint preparation. Grind the tungsten using a 250-grit or finer grinding wheel so that the grind marks run lengthwise with the tip, which helps control arc wander. If the tungsten accidentally becomes contaminated during the weld process, cut back 1/2 inch from the contaminated point and reshape the tungsten. Simply grinding off the surface at the contaminated point won’t work since there’s no way to determine how deep the contamination runs. The tungsten should extend no more than one and a half times the diameter of the tungsten from the end of the nozzle. This increases visibility and reduces the possibility of touching the tungsten to the weld puddle.
- Filler metal: There are three major classifications of TIG filler rods used to repair aluminum: ER4043, ER4943 and ER5356. ER4943 is a general-purpose filler rod to use if you are unsure of the exact chemical makeup/composition of the part because it offers many of the fluidity characteristics of ER4043 while giving similar tensile strengths as the ER5356. ER5356 is used to weld anodized aluminum because it provides proper color match after the anodizing process is completed. NOTE: if an ER4043 rod is used and the part is to be anodized, the weld zone will appear as a dark gray area after anodizing is completed. Use an ER5356 filler rod instead if the part is to be anodized and there will not be any discoloration in the weld zone. The necessary diameter of the filler rod is determined by the thickness of the broken part. Common rods are 3/32 inch and 1/8 inch in diameter. To ensure the filler rod is free of contaminants that can result from open storage or exposure to dirty conditions, use a pad to clean the rod before welding. Do not use sandpaper to clean dirty filler rod, as this could add alumina sand to the filler.
Proper technique for TIG welding
Whenever possible, situate the part in a flat position. Hold the tungsten 1/8 inch away until the arc is initiated. Do not to touch the tungsten to the aluminum at the risk of contaminating the workpiece. Modern inverters such as Dynasty® TIG welders allow the operator the ability to use Lift-Arc™ starting. However, Lift-Arc is not recommended with conventional AC machines as the tungsten can become contaminated using this technique.
A good practice is to maintain an arc length equal to the diameter of the tungsten you are using. For example, if you are using 3/32-inch tungsten, you should have a 3/32-inch arc length.
Once you've started the arc, the first pass on used aluminum is going to be dirty even if you have cleaned it perfectly. Aluminum acts as a sponge and there are typically contaminants embedded in it. For this reason, it may be a good idea to weld the first pass down the length of the beveled joint without adding any filler rod. This will allow you to boil out as much contamination as possible. Then wire brush off any contaminants that came to the surface on the first pass.
Begin to add filler rod on the second weld pass. There may still be some contamination on the surface of the weld bead, but the joint will become cleaner with each pass. Brush the joint and repeat this process until you have completely built-up and repaired the part. If pinholes or porosity show up, grind them down, brush the area and weld again. This ensures a stronger weld and helps remove even more contaminants.
Repairing holes with TIG welds
The TIG welding process is slightly different when repairing a hole in a part instead of a crack. First, you need to clean out the hole with a small stainless steel brush or drill through the hole using a clean drill. Then weld around the edges of the hole to remove any contaminants without adding filler rod. Next, wire brush the weld surface to remove any dirt or contaminants.
Once the hole reaches good material you can begin welding and adding filler rod. Use a very low heat and a small diameter filler wire (.030 or .035-inch diameter) to carefully fill each hole. Take caution, as too much heat may create more pinholes, especially when repairing cast aluminum.
Weld in a circular pattern around the hole to build it up from the outside in. Fill in the hole and then weld around the top of the hole to flatten out the weld. If cosmetic appearance is important, you may grind off any weld that may be protruding from the topside, but in many cases it doesn’t harm anything to leave it.
Successful part repairs
Always remember to use the utmost discretion when repairing aluminum parts for your truck. First determine whether the part can and should be repaired and take the proper precautions during the TIG welding process to make a solid weld. After all, the goal is to get the part back into action, along with the satisfaction that comes with saving time and money because you did it yourself.