Types of Welding Used for Aluminium

Welding aluminium is unique, compared to welding other common materials like steel, because of its chemistry and tendency to crack.

To successfully weld aluminium, you need to follow procedures and special considerations. Some of these considerations include:

• Choosing the right filler material.

• Storage of aluminium.

• Cleaning of the base material.

• Selecting the correct welding techniques.

Characteristics of Aluminium

Welding is a chemical process that involves the reduction of hydrocarbons. To achieve excellent results, you need to understand the characteristics of aluminium, especially during welding.

The most crucial factor to note when welding aluminium is that it has an oxide layer which is harder than the metal itself. This layer is what protects the metal from abrasion and corrosion. It can also act as an insulator during welding, which can create some challenges.

Why is Welding Aluminium Challenging?

Welding aluminium is unlike welding steel or iron. There are several challenges you should expect to run into because of the unique composition of aluminium. The greatest of these challenges is porosity and thermal conductivity.

• Porosity – When welding aluminium, porosity becomes a major challenge because hydrogen is soluble in liquid aluminium. During welding, aluminium and the filler material will both become liquids hence absorbing hydrogen. The hydrogen can be held inside the solution, but once the two metals start to solidify, they can no longer handle the hydrogen. It forms bubbles that are trapped inside the metal, causing porosity.

• Hot cracking – Unlike with steel, the presence of hydrogen will not cause the weld in aluminium to crack. But it is possible for hot cracking to occur. The best way to solve this challenge is to ensure you pick the right filler material.

• Thermal conductivity – Aluminium has a high thermal conductivity. The cold areas of the metal are continually trying to pull the heat away from the welding area. This makes it hard for the weld to penetrate. Opting for higher heat inputs will help to attain the critical temperature for the weld to penetrate.

Types of Welding Used for Aluminium

Now that you’re aware of some of the problems you might encounter when welding aluminium, here are some of the best types of welding techniques that you can use when working with aluminium. Usually, the welding techniques are similar to those used to weld steel sheets with moderate changes to address the chemical properties of aluminium.

Gas Tungsten Arc Welding (GTAW)/ TIG

This is the most common method of welding aluminium. It is also known as Tungsten Inert Gas welding. This method doesn't require mechanical wire feeding, which saves you the problems that come with feedability issues. Using this method, you will feed the filler material into the puddle by your hand. One of the reasons this method is highly preferred is because of the new and clean weld it produces. It also prevents contamination of the work area by the atmosphere.

Gas Metal Arc Welding/ MIG

MIG welding uses an electrode for the wire that is continually fed at the base of the weld. The wire is shielded by inert gas and in some instances, a gas mixture to prevent the absorption of hydrogen. The method is often messy because of the trace of tiny metal beads that are left behind as a result of using the spray transfer method.

For experienced welders, this method is more controllable with a cleaner result. But more often than not, you will have to spare some time to clean up the weld.

Arc Welding

Arc welding is the very first welding technique ever discovered. This technique uses a power supply to melt and join the aluminium sheet. Although it is the most cost-effective type of welding aluminium, it should only be completed by an experienced welder.

Resistance Welding

Resistance welding is also a possibility when working with aluminium. But it's not without challenges, mainly because of aluminium thermal conductivity properties. To complete the weld successfully, you will need to use special tips, welding equipment and take time developing the parameters.

Electron Beam Welding and Laser Beam Welding

Beam welding produces a high-power density, which is excellent because it prevents a cold start. But both laser and electron beam welding techniques are not without challenges. With laser welding, light reflectivity is the primary concern. Porosity is also a concern, but with proper shielding gas optimisation you can prevent it.

Electron beam welding is more manageable. It’s done in a vacuum, so you don't have to worry about porosity and it doesn't use light as an energy medium. 

Choosing the Right Filler Metal

It's not enough that you choose the right welding type for aluminium. It would help if you also chose a suitable filler metal to achieve the desired results. There are numerous factors to consider and various filler metals.

The best approach is to use a selection chart while considering the weld characteristics required by the application at hand. There are eight vital properties you need to consider when choosing the filler metal. These are:

• Crack sensitivity

• Corrosion resistance

• Ductility

• Colour match

• Elevated temperature service

• Strength

• Toughness

• Post-weld heat treatment

You can also use a filler metal selector app that will provide you with an array of the best filler metal based on the base material.

Best Practices When Welding Aluminium

For good results, you will need to pair the best welding types and filler metal for aluminium with some best practices.

• Don’t weave – Weaving is common when welding steel but shouldn't be used in the case of aluminium. A stringer bead is preferable.

• Clean the aluminium sheets – Clean the base material thoroughly before welding. Removing contaminants like oil, dirt and dust reduces chances of porosity and improves the final results.

• Remove the oxide layer – Use a new stainless-steel brush to remove the oxide layer. Without removing the coating, you could run into problems when you start welding.

• Proper storage – Store the aluminium sheets properly to prevent porosity. Store the sheets indoors and preferably vertically as opposed to piling them on top of each other.

Welding aluminium is an easy task if you take the time to prepare and follow these tips.