Within welding, one process of sheet metal fabrication, aluminium is often referred to as one of the more difficult materials to work with. We discuss what makes aluminium difficult to weld and best practices for producing high-quality finished parts.
Aluminium proves more challenging to weld than other alloys such as mild steel due to the characteristics which it is made up of. The main differences are thermal conductivity and issues with porosity.
The thermal conductivity (measure of how fast heat runs through a metal) of aluminium is about five times higher than that of a low-carbon steel therefore it dissipates heat very quickly.
Issues with porosity is another characteristic which makes welding aluminium more difficult. If this occurs, then pores (or small holes) will form in the solidifying weld metal.
Having a melting point of around 660°c, dependent on grade, means burning through the workpiece and creating an unwanted hole is far more common than with other materials such as mild steel which has a melting point of between 1350°c – 1530°c, again dependent on the grade.
Also, aluminium has an oxide layer which acts as an insulator and can cause arc start problems, whilst also burning at a far higher temperature (around 2070°c) than the base material. Due to the high heat required to weld through the oxide layer, this again runs the risk of a “burn-through”.
Cleaning the Material – before removing the oxide layer, Aluminium should be cleaned thoroughly. Removal of water vapour, oil and grease can be done by using a mild alkaline solution such as a strong soap or with an organic solvent such as acetone. Do not wire brush at this stage as this runs the risk of scratching the surface and pushing oil and grease into these scratches which is extremely difficult to clean.
Removal of the Oxide Layer – This can be done a number of ways with a common method being to use a stainless-steel wire brush (which has only been used for aluminium), either manual or powered. Other methods include immersing in strong alkaline solutions before rinsing with hot water and drying, and by using bottled oxide-removal solutions which are phosphoric or hydrochloric acid based.
Ensure Consumables are Set Correctly and in Good Condition – porosity can be caused by the consumables used when welding aluminium. For example, if the hose connects are not tight enough then this risks air being pulled into the line. If though, the gas lines and hoses are new or at least in good condition then this decreases the risk of porosity occurring.
Use the Correct Shield Gas – a shielding gas is used to prevent exposure of the (aluminium) weld pool to non-desired gases such as oxygen. In most instances for Aluminium, a pure 100% Argon shield is used as it provides an improved cleaning action and good arc stability, among other things but in instances for specialist projects or higher heat characteristics are needed, this may be upgraded to an Argon and Helium mix
“At ADS Laser Cutting, we will decide on which method to use based on factors such as the thickness of the material and whether it is a specialist job which requires extra attention to detail.
Our team are highly proficient in both areas as we use the latest technologies and processes within TIG and MIG Welding. We also have a long-standing team who have proven experience with some of the more difficult projects involving aluminium.”
Tungsten Inert Gas (TIG) Welding is most suited for aluminium welding although Metal Inert Gas (MIG) Welding is still a viable option dependent on the project. At ADS Laser Cutting, we will decide on which method to use based on factors such as the thickness of the material and whether it is a specialist job which requires extra attention to detail.
Our team are highly proficient in both areas as we use the latest technologies and processes within TIG and MIG Welding. We also have a long-standing team who have proven experience with some of the more difficult projects involving aluminium.
Tungsten Inert Gas (TIG) Welding Aluminium
As mentioned, this method is typically seen to be the most suitable for welding thinner aluminium and is more controllable, primarily because it does not require mechanical wire feeding. The filler material is instead fed into the puddle by hand.
TIG Welding is also a far cleaner method than others, which means it is less likely that the aluminium will end up being contaminated during the process.
Most alloys are welded using Direct Current (DC) flows, with this being a constant current which flows in one direction. With Aluminium however, when using TIG Welding an Alternating Current (AC) flow is always used, where the flow alternates constantly from positive to negative and back again (a bi-directional current travelling in two directions). This is due to the oxide layer mentioned earlier. The AC cycle helps to penetrate the oxide layer, whilst also providing a “cleaning” type action.
TIG Welding is a slower method than others and is typically not used on thicker materials or where speed is an important factor, but where instead the importance is placed on quality and appearance this is the preferred option.
Metal Inert Gas (MIG) Welding Aluminium
MIG Welding is an effective method for certain aluminium projects, as it has higher deposition rates and faster travel speeds than TIG Welding. Typically, this would be used on 3mm thick and above as it is not as controllable as TIG Welding which as mentioned is the preferred option for thinner aluminium. It is possible to MIG weld aluminium below 3mm, but specialist equipment and a high skill set are required for this.
MIG Welding uses a mechanical wire feeding system, therefore using a “push-pull” wire feed or Spool Gun helps to avoid tangles or jamming as aluminium wire is much softer and not as stiff as steel wire. Otherwise, not using methods such as these, can result in “bird-nesting” inside of the cable liner.
Generally, MIG Welding is used for thicker materials due to it being a quicker process and depositing more filler material, but in instances where thicker materials require a clean finish such as on specialist jobs, then TIG Welding would be used.
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