How to Weld Aluminum?

Aluminum is the second most frequently used alloy in the world. Its density is three times less than that of iron. Among its most important advantages, in addition to its light weight and high strength, are its low weight and resistance to rust.

In addition to its anticorrosive properties, aluminum also has a low melting point and good electrical conductivity. Not surprisingly, more and more people want to weld aluminum – its wide use is noted in the food, automotive, aerospace, construction as well as electrical engineering sectors. By far the biggest role of aluminum and its alloys is in the automotive industry.

Placing aluminum components in vehicles makes them much lighter than those made of other metals, so the weight of the vehicle is lower, resulting in more efficient fuel consumption and lower CO2 emissions into the atmosphere.

Correct welding process

For welding aluminum, we need to choose the correct welding process.

Any welding process that uses a flux, which includes stick welding, flux cored arc welding, stick weld aluminum and submerged arc welding, are generally not effective methods for this material.

Welding processes determine not only what our aluminum welding will look like, but also what kind of welder we need. In most cases, we’ll need two separate welding machines to weld aluminum using two methods – and that’s because most semi-automatic welding machines don’t have the alternating current in the TIG method, which is required to weld aluminum.

So we have two methods to weld aluminum:

• TIG Welding (Tungsten Inert Gas)
• MIG Welding (Metal Inert Gas)

TIG welding machines are most often used for welding aluminum. This is a gas-shielded arc welding method, it is a guarantee of receiving welds of the highest quality. With this method, the entire process is carried out by an infusible and heat-resistant tungsten electrode, with the participation of which a welding arc is produced that heats and liquefies the aluminum.

The MIG welding method of aluminum is used when the thickness of the metal exceeds 1 mm. The process itself requires the use of a filler wire, which is fed through an classic MIG torch or spool gun by mechanical wire feeding system. MIG welding of aluminum can be difficult even for those welders who are experienced in this welding method, as it is very different from MIG welding mild steel.

MIG welding aluminum

The MIG welding method involves welding using a similar inert shielding gas, such as helium or argon. Welding is carried out using an electric arc, produced between a fusible electrode and a part of the aluminum to be welded.

The welds produced in this way are of good quality, welding is efficient, and welding costs are low. In MIG welding, depending on the current parameters, we can distinguish between the short-circuit method and the spray method. When welding aluminum, the current does not need to be very high for the droplet transfer to be spray, because the melting point is much lower compared to steel.

How to weld aluminum with MIG welding process

Aluminum welding equipment needed

The first thing we need to start with in the case of MIG welding aluminum is to replace the cartridge in the MIG torch from a standard metal one to a Teflon one. This type of insert will improve the sliding of the aluminum wire in the holder and prevent deformation. You can skip this process if you have the right spool gun.

The same applies to the rollers in the feeder, it is necessary to replace them with ones whose groove shape resembles the letter “U” – this is also aimed at limiting the deformation that can occur on the welding wire.

To make sure that the wire will be accurately fed at the welding spot, our device should be equipped with a 4-roll wire feeding mechanism. After installing the wire in the holder, the current tip should be replaced with one marked “A” for welding aluminum – due to the expansion of aluminum during heating.

As for the shielding gas, pure argon will be the best.

Useful features for MIG welding aluminum

Modern welding equipment also gives us the option of pulsed current welding, a feature that will be useful for welding thin aluminum parts. For welding aluminum, it is necessary to use argon as a protective gas and to heat the material before welding.

It is not necessary to heat the material if we use a mixture of Ar+ (50÷75%). It has the protection gas, because Helium increases the thermal power of the arc. The last thing to do before welding is to properly clean the material from aluminum oxide layer.

First, degrease the welded surface using, for example, extraction gasoline and in the next step remove oxide coatings with a stainless steel brush. The MIG method makes it possible to achieve a deep penetration during welding, so metal sheets up to 6 mm thick do not need beveling.

It is only necessary to leave a gap of about 1 mm between the edges. In the range of 6-15 mm, the edges of the plates are beveled on the V (angle of 70°). with a threshold of 2-5 mm and a gap between the edges of 1-2 mm. When there is the possibility of two-sided welding, sheet metal with a thickness of more than 15 mm should be beveled on X (angle 70°) with a threshold of 2-3 mm.

In addition to the need to bevel the edges of the sheets, it is also required to thoroughly degrease and clean them from aluminum oxide – stainless steel wire brush will be very helpful here.

Proper preparation of the material in MIG method

Material prepared in this way will give us the assurance of a properly made connection free of defects.

Short-circuit welding is more useful when welding thin sheet metal, and also when welding in forced positions. Up to a thickness of 25 mm we use 100% argon, for sheet thicknesses of 25-50 we use argon with 10-35% helium, and for thicknesses above 50 mm we use a mixture of argon with 35-70% helium.

Due to the high thermal conductivity of aluminum in the use of helium mixtures with high ionization energy, welding currents are similar to those for welding steel but arc voltages are higher. The melting point of aluminum is lower, in order to maintain a suitable stitch cross section the welding speeds are much higher. With the introduction of the pulse welding function in welding equipment, it has been possible to achieve joint reliability as in the TIG method and reduce the risk of hot cracks.

How to guide the welder’s torch in the MIG MAG method?

Regardless of the thickness of the edges to be joined, it is most advantageous to weld from left to right. The spool gun should be set almost perpendicular to the sheets (the angle of deflection of the gun not more than 10-20°).

Weld without interruption and as short an arc as possible (the distance of the gas nozzle of the gun from the material should not exceed 10-15 mm). Using this method, you can weld in horizontal, vertical and wall positions. Due to the high speed of the process, it is currently the most economical of the welding methods.

The MIG MAG method used to be used only for less responsible joints, due to the microporosity of the welds and the resulting decrease in strength. Thanks to modern welding equipment and increasingly better quality materials, today the joints made with mig machines are good enough in terms of strength.

Both semi-automatic and automatic welding allow welds to be made in all positions, including vertical and wall positions.

Thickness of material in the MIG welding process

TIG welding aluminum

TIG welding is most commonly used to weld thin sections of stainless steel, non-ferrous metals such as aluminum, magnesium and copper alloys. It is a much slower process than most other welding techniques.

It is also a much more complex and difficult weld to master, as it requires a great deal of control and dexterity on the part of the welder. The welder in the TIG method must maintain a proper, short arc length, making it a process that requires great care to prevent the electrode from contacting the workpiece.

Not every welder that allows TIG welding will have the ability to weld aluminum. A large proportion of welders on the market that offer TIG in addition to MMA or MIG welding methods can only weld with direct current, which excludes the welding of aluminum.

To weld aluminum, we need a welder with an AC mode. Such welders most often have “AC/DC” in their name, which means that we can weld with them with direct current and alternating current.

What you need for TIG welding of aluminum?

To weld aluminum in the TIG method, you need:

• TIG AC Welder
• TIG welding torch
• Shielding gas
• Tungsten non-consumable electrode

Useful features for TIG welding aluminum

TIG welding, or non-fusible tungsten electrode welding in an inert gas shield, can be used with very thin aluminum, less than 1 mm. The upper limit of metal thickness is about 10 mm. Electrodes made of a material with a very high melting point are used for welding, and their appropriate shape ensures stable glowing of the arc.

The TIG method allows the use of alternating current (AC), which, in the case of joining aluminum, gives great results in obtaining a good quality weld and allows the weld pool to be kept clean. This is influenced by the effective removal of oxides formed on the surface of the metal.

Material thickness and current intensity

The current intensity is selected according to the thickness of the material as are the nozzle diameter and gas flow. The diameter of the tungsten electrode is selected so that there is a current of 40 amperes per 1 mm. The diameter of the welding rod should correspond to the diameter of the welding electrode.

When welding thin sheets in the sub-low current position, it is advantageous to heat up the tungsten electrode by striking the arc on the graphite plate and then transferring the arc to the welded parts.

Guiding the welding torch in the TIG method

The alloy is fed into the welding pool by advancing the wire in a step-back motion. This involves advancing the rod into the weld pool and then, after the end of the rod has melted, moving it back enough so that the end is outside the highest temperature zone.

The technique of welding thicker aluminum parts in the sub-lower position, is slightly different. The higher welding current makes the welding arc blast much stronger and the welding pool is also larger. Any introduction of the wire into the welding arc zone causes a strong disturbance of the arc, splashing of liquid metal and contact between aluminum and tungsten, resulting in the interruption of welding.

It is necessary to maintain the continuous passage of alloy into the welding pool. The wire should be inclined to the workpiece at a very small angle. Depending on the thickness of the parts to be welded, single or multilayer welds are made. Up to a thickness of 6 mm, single-layer welds can be made, above this thickness multilayer welds are made.

Welding Aluminum – FAQ