From shipyards and aerospace applications to general fabrication, operations choose to TIG weld aluminum when they need to produce high-quality welds with premium aesthetic quality.
Specific applications range from small, intricate components that cannot be MIG welded without burnthrough to much larger weldments that require porosity-free welds for critical applications.
The first step in creating high-quality TIG welds in aluminum is choosing the right filler metal for the job. In addition, paying attention to best practices for weld preparation, machine setup, and filler metal storage and handling are also key factors in producing optimal TIG welds.
To implement some best practices for TIG welding aluminum, it’s important to understand the common challenges involved with welding it. Aluminum has a higher thermal conductivity rate than other materials such as steel or stainless steel. As a result, it draws heat away from the weld pool quickly and requires more energy to achieve penetration. However, too much energy or travel speeds that are too slow will create a larger heat-affected zone (HAZ). This makes proper heat input critical when welding aluminum.
The biggest challenges to overcome are porosity, lack of fusion and overheating the base material. Porosity can come from improper cleaning, leaks in connections or gas hoses, and high relative humidity causing moisture accumulation on the material or (water-cooled) torch if they cross the dew point.
Lack of fusion can happen when operators use a travel speed that is too slow, causing them to ride the molten filler puddle. It can also result if the operators don’t use enough amperage to melt the base material or fail to remove the aluminum oxide. This oxide layer melts at approximately three times the temperature of aluminum and is also an insulating barrier.
Overheating can go hand in hand with lack of fusion. Operators may ride the puddle and sit in one place in an effort to establish fusion, but this can add too much heat into the base material, which can reduce the strength of the HAZ.
In addition to these common challenges with aluminum, the TIG process typically requires more operator skill. It is a slower process overall compared to MIG welding, which makes it a more expensive process for operations to use.
For common best practices that help optimize results, consider these five tips that can help deliver better performance when TIG welding aluminum.
1. Choose the right filler metal
Typically, any filler metal used for MIG welding can also be found in TIG rod form. Some of the most commonly used alloys for TIG welding aluminum are 4043, 4047, 4943 and 5356. The 4xxx series filler metals share many similar characteristics.
A 4043 rod is a good all-around filler metal for general fabrication. While it has a lower melting temperature and provides lower distortion (thanks to its silicon content), it doesn’t provide the strength or toughness that a 5xxx series filler metal can. A 4047 rod also has a lower melting temperature but includes 12 percent silicon content, so it has the least amount of contraction forces and distortion of the aluminum filler metals. Due to its higher silicon content, a 4047 rod also results in a very shiny weld, making it popular for aluminum toolboxes.
A 4943 rod can be used interchangeably with a 4043 or 4047 filler metal. A 4943 rod still has similar silicon content that helps with reduced shrinkage stress and less distortion, but it also provides strength that is more comparable to a 5356 alloy. Of these commonly used rods, 5356 provides the most strength and ductility, but there are many other factors that come into play when selecting a filler metal. Always refer to a filler metal selection chart for aluminum to choose one that is best suited for a particular application.
TIG filler metal rods are available in standard 36-in. lengths and diameters that range from 1/16 in. to 5/32 in. for some alloys. With large weldments, choosing a larger diameter rod can benefit productivity by filling the weld joint faster. TIG filler metals come in many packaging options, such as 1-lb. tubes and 10-lb. and 40-lb. boxes.
2. Prep the base material
The steps needed for cleaning the base material depend on the quality of weld the operation needs to achieve. Critical applications typically require a more careful level of cleaning before
TIG welding aluminum while more cosmetic applications may not brush off the oxide to prevent having scratches next to the welds.
When preparing aluminum for TIG welding, it’s best to clean the surface with a paper towel or a clean rag and a cleaning agent like acetone. This removes contaminants like dirt and hydrocarbons, such as oils, paint or adhesive residue. It’s not recommended to use shop rags because these may still contain dirt or oil.
After removing the surface contamination, remove the aluminum oxide layer that serves as an insulating barrier with a stainless steel wire brush, which helps reduce chances for weld contamination that could cause porosity. Be sure to use a new stainless steel wire brush or one dedicated for use on aluminum to avoid cross contamination from other materials.
3. Adjust machine setup and parameters
The most typical setup for TIG welding aluminum involves using an AC TIG welding power source with 100 percent argon shielding gas. Be careful not to undersize the machine. The general rule of thumb is to have 1 amp per 0.001 in. of material thickness. So, welding a 1/4-in. fillet weld would require a 250-amp machine. An undersized machine wouldn’t provide enough amperage for the job, resulting in too little heat to properly establish the weld puddle or resulting in the need to preheat the part. It can also put additional stress on the power source by welding at maximum output for extended periods of time.
Using DC TIG for welding aluminum is not a typical setup, but it can be done. DC TIG welding requires a helium or helium-and-argon-mix shielding gas, which provides a much hotter welding arc and deeper penetration. But because the DC electrode-negative process doesn’t have the cleaning action that the electrode-positive portion of the AC process does, the initial steps for cleaning the base material and removing the oxide layer are critical.
Many of today’s TIG welding power sources have some type of preset function to help ensure operators are welding within a range of proper parameters. Using preset parameters can be especially helpful for less experienced welders. More experienced welders can adjust the frequency and balance to tailor their arc cone. The higher the frequency setting, the tighter the arc cone will be for a narrower penetration profile and less arc wander.
Adjusting the balance setting changes how much time is spent in electrode-negative versus electrode-positive mode. A balance that is more on the electrode-positive side provides more cleaning action to strip away the oxide layer and clean the base material during welding. The higher the electrode-negative side, the more heat goes into the material for faster travel speeds and less of a cleaning band outside the weld area. It’s important to balance the two, depending on the condition of the material and the needs of the application.
4. Follow the “hot and fast” rule
The best way to overcome lack of fusion or other issues when TIG welding aluminum is to weld hot and fast. That is, start with enough amperage to establish the puddle quickly (within a second or two) and then start welding immediately and maintain a good travel speed. Some operators are prone to slowing down to achieve better penetration. Don’t dwell in the weld puddle or move too slowly because this puts more heat into the base material than necessary and can greatly reduce the strength of the HAZ.
5. Handle and store filler metals properly
Following best practices for storing and handling TIG filler metals helps reduce the risk of contamination that can result in porosity and weld defects. Keep separate storage containers for each type of filler metal instead of mixing them together and be sure to keep the rods covered and stored in a dry location with minimum temperature fluctuation.
If the filler metals aren’t stored where parts are welded, bring the rods into the welding area at least 24 hours prior to welding with them. This allows them to acclimate to room temperature. Storing filler metals in a cool, air-conditioned office and then taking them into a hot shop to weld can cause condensation – moisture that can add porosity to the welds. Multiple dew point crosses can also cause the oxide layer to grow thicker on the aluminum rod.
The properties of aluminum make welding it different from other materials. Operators can improve results by understanding the basics of aluminum and following best practices for choosing filler metals, cleaning the base material and adjusting parameters.