Features of root bead formation in plasma arc welding of aluminum alloys using asymmetric variable polarity current

This study investigates the characteristics of root bead formation in plasma arc welding (PAW) of aluminum alloy 1560 (Al–6.0%Mg–Mn system) using asymmetric variable polarity current (AVPC) under two modes: the keyhole mode and the use of backing plates with forming grooves. It was established that maintaining a constant gap of 0.8–1.0 mm between the joint edges is necessary to improve weld bead formation and reduce the molten metal volume. This also prevents the formation of oxide film inclusions. The study demonstrated that when using backing plates with forming grooves of the standard tungsten inert gas (TIG) profile, a plasma jet reflection effect from the groove surface is observed. This results in the formation of defects in the root bead. To eliminate this phenomenon, a backing plate with a specially shaped groove was proposed for forming the lower part of the weld. The AVPC welding process in keyhole mode produces welds that are 20% narrower than those obtained when welding on a backing plate with a forming groove at identical welding speeds. However, welding with full penetration of the plasma jet is more difficult to reproduce and requires an exact balance of welding parameters.