The invention relates to a plasma arc welding process and a plasma arc welding device for aluminum and its alloys, which process comprises at least one step of initiation of a pilot arc by means of an auxiliary current which is delivered by an auxiliary current source and flows in a pilot-arc circuit, one step of feeding with plasma gas, one step of initiation of a main arc by means of a main current which is delivered by a main current source and flows in a main circuit, one step of cyclic variation of the polarity of the main current so as to obtain at least one phase of descaling the material to be welded with a first current polarity and at least one phase of welding the material with a second current polarity, and in which process the supply of auxiliary current to the pilot-arc circuit is stopped during the descaling phase and the main circuit and to the pilot-arc circuit are supplied with main current.
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