The influence of positive polarity time on GTAW AC of aluminium

Abstract

In this work, experiments were carried out to determine the welding behaviour of aluminium 1200 based on an increase in the activation time of the positive polarity for tungsten inert gas AC welding of this metal. To achieve this objective, a series of experiments was developed, in such a way that the intensity of the electrical current in the positive and negative polarities was the same; only the duration times in each polarity were modified. During the experiments, the current and voltage signals were acquired. In this way, the arc voltage and potential could be determined for each condition tested. In terms of the fusion behaviour, an increase in penetration and in welded areas was verified to the extent that longer positive polarity times were used. This behaviour is different from that commonly indicated in the literature about welding processes with non-consumable electrodes, which suggests a reduction in penetration with an increase in the positive polarity activation time. However, this trend grows constantly during the experiments from a determined point, where the positive polarity activity times are greater than 4.0 ms in a total period of 20.0 ms. The use of a minimum positive polarity time (1.3 ms) was shown to be effective for cathode cleaning, as it produced welds with satisfactory fusion characteristics and with minimum wear to the tungsten electrode. The good fusion capacity obtained in welds produced with long positive polarity times was attributed to phenomena arising from the emission of electrons due to the field effect that occurs during the positive electrode phases.