Comparison among the environmental impact of solid state and fusion welding processes in joining an aluminium alloy

The life cycle assessment (LCA) methodology was used to evaluate the environmental impact of friction stir welding (FSW) of AA5754-H114 aluminium alloy sheets. FSW was performed under different values of rotational and welding speeds to analyse the influence of the process parameters on midpoint category impacts. Pin tool wear and mechanical properties of joints were also evaluated. The functional unit chosen was related to the weld efficiency; furthermore, the weld length was set equal to 170 mm. The pre- and post-processing stages were also considered. Raw materials, energy and all inputs associated with each stage of product life cycle were collected and evaluated to analyse the environmental impact index. The results showed that, irrespective of the rotational speed, the lowest welding speed investigated leads to the highest energy consumption and, consequently, to the highest values of the midpoint category impact. On the contrary, at the highest welding speed, the environmental impact assumes the lowest values. By concerning the rotational speed, its effect on the midpoint category impact is strongly reduced compared to the one given by the welding speed. A performance index, obtained by considering both the midpoint category impact and ultimate tensile strength of the joints, was also defined. Finally, the environmental sustainability of FSW was compared to the one of two different fusion welding technologies, namely gas tungsten arc welding (GTAW) and laser beam welding (LBW). The results showed that FSW was characterized by midpoint category impacts much lower than those of the GTAW, whilst such discrepancies decreased with the LBW.