Incremental forming of friction-stir welded aluminium blanks: an integrated approach

This study deals with an experimental investigation of the influence of friction stir welding parameters on the subsequent formability during incremental forming of aluminium alloy 6082-T6 blanks. Five welding conditions are considered, based on different combinations of rotational speed and feed rate. Truncated cones are chosen as benchmarks for single point incremental forming and tested up to their rupture limits. Formability is inferred measuring the cone height values, together with strain distributions, as recorded on the outer surface. The results clearly highlight the detrimental influence of a high feed rate of 100^− 1at the friction stir welding stage, leading to a significantly reduced formability in incremental forming. Regarding other parameters, formability levels are similar to those of the unwelded blanks. Local mechanical properties are investigated by means of hardness measurements, to assess the evolution through the weld, and conventional tensile tests. Digital image correlation is used to properly capture the highly heterogeneous strain field and as a result, to estimate the local yield stress levels. The stress mismatch between the heat affected zone and the nugget zone presents the same trend as the formability. Finally, scanning electron microscopy observations of the fractured samples in tension highlight more differences between the base material and the welded specimen than between the different welded ones. This study therefore emphasises the importance and relevance of an integrated mechanical design approach, considering both welding and forming processes as a whole.