At Eng-Weld we know that different projects require different methods and tools, in this way, welding different materials using both MIG and TIG, requires you to choose the right tools to get your desired results. Working with aluminium is difficult due to its high conductivity and low melting point, while the oxidised film on the aluminium surface has a different melting point to the aluminium itself and is therefore tricky to work with for even experienced welders.
Aluminium is suitable for both MIG and TIG welding, the difference between the most suitable method comes from the thickness of the material, for thicker welding MIG is recommended as it can do the job faster, whereas for thinner aluminium TIG is more suitable. In this article, we will be looking at Aluminium TIG welding.
In most cases, TIG welding is used when working with aluminium. Due to the increased control you have when using this method, you have the ability to prevent the aluminium from overheating.
The selection of a filler rod is a critical aspect of TIG welding, the use of both hands affords the welder excellent control, choosing a filler rod that is similar to that of the parent metal is essential, as having a similar tensile strength to the parent metal reduces the chances of cracking in the weld, along with decreasing the chances of other weld discontinuities. As you do not use mechanical feeding for TIG welding, otherwise known as GTAW welding, you eliminate the feedability issues that are often associated with welding methods that use automated wire feeders.
TIG welding, due to the need to use two hands in order to operate both the welding torch and the filler material simultaneously, forces you to take more time and therefore is a better option where quality and attention to detail are important. As you feed the filler yourself, you also get work that is spatter free, which results in a cleaner finish.
The correct TIG welding machine
TIG welders that are suitable for aluminium typically have the following characteristics:
- AC-powered, the alternative current makes it more suitable for dealing with the oxide film on the aluminium surface.
- The output power range is up to 500A on the larger TIG machines.
- The welding should feature a low amperage, meaning the arc stability must not exceed 10 amperes.
- Its duty cycle should ideally be between 50% – 80%, although this may differ.
For smaller and more precise welds and projects involving aluminium, TIG welding is better suited due to the two-handed operation. This forces the welder to be more methodical and work at a slower pace, which allows greater care to be taken, essential when working with thin aluminium. The method also yields a cleaner and smoother finish as it should be defect-free whilst ensuring a reliable joint is made. However, this more time-consuming approach, coupled with the increased cost of the materials and equipment does make this a more costly approach to aluminium welding.
There are major differences between MIG and TIG welding, especially when working with aluminium. Each approach has its drawbacks and advantages.
TIG welding would be better suited for your aluminium welding work if:
- Your welding needs to be aesthetically pleasing and offer a beautiful finish, this is achieved through identical weld beads.
- Great attention to detail is required.
- Your work must be spatter free, which results in a cleaner finish.
- Your work area is extremely clean.
- The projects are small in nature.
- The weld does not involve cast iron.
- You wish to have more control over your weld.
- Stronger welds are needed.
- Less maintenance is needed, as with MIG welding, there is no sanding or cleaning required between jobs.
The Gases Used
During TIG welding, inert gases are used in order to protect the weld pool from contaminants such as moisture, which have detrimental impacts on the integrity of the weld. Typically, when working with aluminium, Argon gas is used.
As an inert, noble gas, it is colourless, odourless, and most importantly from a welder’s perspective, it is a non-chemically reactive gas. This means that the melted aluminium will not react with the shielding gas, ensuring that the weld remains pure.
Although it should be noted that Argon is frequently combined with Helium, Hydrogen and Carbon Dioxide, as a mixture can provide certain properties that Argon alone cannot. For example, by combining Argon with Helium, the welder is able to achieve deeper penetration, whilst also ensuring that the weld pool remains fluid. The addition of Hydrogen will give a similar effect to that achieved by using Helium, but much stronger.
The key is to use non-oxidising gases, as these will destroy the tungsten electrode.
TIG Welding and Tungsten Electrodes
Selecting the correct TIG welding machine requires you to carefully consider the task at hand, along with other variables, such as the use of an alternating or direct current, and the same logic applies when selecting the correct tungsten electrode.
You must consider that not every type of electrode is suitable for use with an alternating current, the predominant current used when TIG welding and working with aluminium, but there are other factors to consider. The specific task will have a large impact on the selection of the correct tungsten electrode, as you can choose from pure tungsten or tungsten that has oxidic additives, which bring different properties.
Zirconium oxide (ZrO2) enables a much more stable arc compared to pure tungsten, all while reducing evaporation, while Cerium oxide gives a tungsten excellent ignition and reignition properties. Lanthanum oxide also has very good ignition properties, while having the added benefit of increasing the service life of the electrode. Pure tungsten meanwhile, enables a very steady arc but does not have the same current carrying capacity, ease of ignition or long service life that electrodes with oxidic additives possess.