Alternating current (AC)
Alternating current (AC) constantly changes direction during welding. In TIG welding of aluminum and aluminum bronze, the positive half-cycle breaks up the tough oxide layer, while the negative half-cycle cools the electrode – so dilution remains low and the weld stays clean.
What alternating current is
With alternating current (AC), the direction of current changes continuously – typically 50 or 60 times per second. In welding, this has a special effect: each half-wave does something different.
Why AC is important for aluminum and aluminum bronze
Aluminum and aluminum bronze form an extremely tough, high-melting oxide layer. The positive half-wave of the AC breaks up this layer and cleans the weld pool, while the negative half-wave spares the tungsten electrode. That's exactly why you weld aluminum classically with AC.
The advantage in surfacing
Because the AC cleans the pool and distributes heat more evenly, dilution with the base material stays low. When surfacing aluminum bronze onto steel, the weld stays shiny gold instead of smeared gray – and the emergency running properties of the filler are preserved to nearly 100 %.