AC Aluminum Welding: Do You Really Know It?

AC is used whenever aluminum welding is conducted by tungsten inert gas welding.

The reason is that aluminum is covered with a layer of aluminum oxide, which makes aluminum welding extremely difficult.

The melting point of the surface oxide layer is close to 2015 ℃, while the melting point of pure aluminum is only 650 ℃.

This means that when the oxide layer covering the surface is penetrated by welding, the pure aluminum below will also be melted, and subsequent welding cannot be carried out.

Welding is effective only when the surface oxide layer is damaged or exposed.

When welding with alternating current, the tungsten electrode continuously switches between the positive and negative electrodes.

When the tungsten electrode is positive, the negative electrons move from the workpiece to the tungsten electrode, and the oxide layer breaks in the process.

After that, when the tungsten electrode is negative, electrons will move from the tungsten electrode to the surface of the workpiece to generate heat, which is necessary for the weld to produce penetration.

Related reading: Aluminum Alloy Welding: Method and Material Selection

AC Aluminum Welding: Do You Really Know It? 1


The welding power source suitable for direct current is equipped with an inverter that generates alternating current.

Many welding machine systems have different settings to set the AC conduction during the positive and negative current conversion.

Users can select from different half waves.

AC Aluminum Welding: Do You Really Know It? 2

For example, the current can flow in the positive range now, and then in the negative range with the same intensity – thus forming a constant rectangle on the waveform.

After using these settings, the oscillogram will be very stable, but for the welder, the huge noise in the welding process will be irritating, making the welder have to wear ear muffs.

Smooth sinusoidal waveform is also possible.

Although this will reduce the noise, it will also lead to the instability of the arc.

In most aluminum welding applications, the combination of the two is the best choice.

The negative current half wave is a rectangle with rounded corners, and the positive current half wave is a sinusoidal pattern.

Vonnex welding system also provides triangle waveform, which can be widely combined with other kinds of waveforms while providing stable high-voltage arc.

The welder can select the most appropriate setting according to the specific application.


AC Aluminum Welding: Do You Really Know It? 3

When purchasing tungsten electrode, the top of the tungsten electrode rod is flat.

When using direct current, the tungsten electrode tip will be cut into a sharp shape.

However, in order to keep the arc stable, the top of the tungsten electrode tip must become a semicircle arc when working with alternating current, so that the arc can be fully controlled.

The semicircular electrode tip is also called “cap”.

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