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The results of thermal efficiency on welding using the modified indirect electric arc technique [Ambriz RR, Barrera G, Garcia R. SI11:10–17] of the 6061-T6 aluminium alloy are presented. These values are in the range of 90–94%, depending on the preheat temperature and were obtained by means of a heat balance that considers the heat input, the amount of molten mass of the welding profiles, and welding parameters during the joining, giving particular emphasis to the data collected during the digitalization of the arc current. Also, some dimensionless parameters were employed in order to determine the approximation grade of the molten pool, the heat-affected zone, and their corresponding approximations to the experimental results.

Results of temperature measurements during welding of 12.7 mm thick AA6061-T6 alloy plates by modified indirect electric arc (MIEA) are presented. This study describes the thermal cycles in the heat-affected zone (HAZ) and also in the fusion zone. Depending upon the position of the transducers, the maximum temperatures measured in the HAZ ranged from 308 to 693°C, these measurements were related with the tensile test results and the failure zone reported previously by the authors (Ambriz et al., SI11:10–17). It was observed that there is a decrease in the mechanical strength of the welded joints, due to the microstructural changes undergone by the AA6061-T6 alloy in which formation of the β′ occurs according to the time–temperature transformation diagram. The inherent cooling conditions of the weld pool observed for the MIEA technique (single welding pass) have made it possible to establish the characteristics of solidification and microstructure for a specific cooling rate.