Aluminum is widely used in industry because of its light weight, corrosion resistance, strength and versatility in many different applications. But when it comes to joining aluminum, beginners can find it to be somewhat challenging.

Aluminum is a very different material from steel. It has a lower melting point, and an oxide coating that needs to be removed prior to welding. The oxide coating forms from a reaction between oxygen in the air and the aluminum itself. The critical step in joining aluminum is making sure the oxide coating is removed prior to welding because it melts at almost twice the temperature of the base material. If we don't remove the oxide, as the material begins to get hot and melt the material appears to have a grey skin on the

surface.

Unlike steel that is welded with direct current electrode negative (DCEN), aluminum is most easily welded using alternating current (AC). The alternating current provides an additional cleaning action of the surface oxides that is not present using the DC power. While some people use DC power to join aluminum in special applications, the majority of industry uses alternating current or AC. We need to make sure that we use a power source that can provide enough amperage and has a duty cycle large enough to perform the work that we plan to do. Another feature that is nice to have on our power source is pulser controls.

The pulser controls allow us to ramp amperage up and down to predetermined settings to help control the puddle and reduce overall heat input. When welding Aluminum With AC power, the best selection for gas is 100% argon. Alternately, we can use pure helium or argon with small additions of helium. Helium adds a significant amount of heat to the arc area but the arc is sometimes unstable, and may discolor the surface adjacent to the weld. On the other hand, argon provides a stable arc, and enough gas coverage to prevent contamination of the weld zone. In the past many have suggested using pure tungsten electrodes for AC welding on aluminum. Others have suggested using the Zirconium type.

Still others use 2% Thoriated or the Cerium doped electrodes. As long as we use an electrode that is large enough in diameter to handle the amperage range that we plan on welding with, most of these electrodes will produce a quality weld in the hand of a skilled welder. We want to watch for any degradation of the electrode on its tip while welding, to determine whether the electrode we have is large enough in diameter to handle the amperage range that we are using. Electrodes are prone to tungsten spitting if the diameter of the electrode is not large enough to handle the operating amperage.

Conventional transformer type AC power sources generally require the use of a rounded tip or a tungsten with a ball shaped end. Inverter power sources with a square wave allow us to weld aluminum using AC and a pointed tungsten electrode. Most quality electrode manufacturers have charts suggesting what amperage ranges are possible using the different diameter electrodes.

For gas tungsten arc welding, we are going to need a torch and all the other torch pieces including the collet body, collet, gas cup and torch tail as well. The collet and collet body must be sized to match the tungsten electrode diameter we intend to use. The torch can be gas cooled or water cooled. It should also be large enough to handle the amperage range we intend to use.

While gas tungsten arc welding of aluminum can be done with the scratch start method, most people prefer a high-frequency start where the tungsten does not have to come in contact with the work surface. Another critical piece of equipment that many people like is some type of remote amperage control. The remote amperage control device can come in the form of a foot pedal or some type of handheld device usually attached to the torch body.

The quickest and easiest way to remove the aluminum surface oxide is by mechanical means using of some type of hand held stainless steel wire brush or a stainless wire wheel attached to a powered die grinder. Many people are successful with the wire wheel using a drill motor as well.

To actually make the weld do the following:

Prepare the electrode and place it in the torch. Turn on the power supply and set the amperage to the correct setting. Turn on the gas and make sure you have the proper flow rate. Get your remote amperage control located in a convenient position. Attach the work clamp to the part you plan on welding. Hold the torch adjacent to the area you wish to start welding at. Start the arc using the remote amperage control. Use enough heat and wait for the puddle to start. Once the puddle has formed add filler metal using the other hand as needed to fill the joint or groove to the desired profile. When finished, ramp down the amperage and hold the torch adjacent to the weld until the gas stops

flowing.

For more detailed instructions on the actual process of welding aluminum, check out our videos on YouTube from the Longevity Learning Lab.