Effect of rotational speed in FSW on the thinning behavior during drawing of tailor-welded blanks

Abstract

The formability of friction stir tailor-welded blanks made from aluminum alloys, used as structural components in the automotive industry, is a concern. Variation in process parameters controls the heat input during FSW, resulting in microstructural inhomogeneity and property differences between the weld material and the base material, which in turn lead to complex stress states. In this work, the influence of rotational speed in FSW on the subsequent formability of tailor-welded blanks (TWBs) is investigated. AA6082-T6 aluminum alloy sheets are welded together at different rotational tool speeds (1,000, 1,500, and 2,000 RPM) while employing a constant traverse speed of 100 mm/min. Post-weld annealing treatment (PWAT) was performed to improve formability, evaluated through square cup drawing tests. The deep drawing process was modelled in Abaqus to investigate the thickness distribution and thinning behaviour using a double-zone modelling approach. Results revealed that the as-welded TWBs exhibited pronounced hardness gradients across the weld region due to the variation in the heat input during welding. PWAT seemed to homogenize the microstructure and mechanical properties, with hardness values stable between 40-50 HV across the entire weld region. This tends to minimize local thinning during forming, regardless of initial weld zone disparities and processing conditions. FEA simulations incorporating the local mechanical properties from each weld region closely reproduced the experimentally observed thickness profiles and deformation patterns. This correlation between the modelling results and the experimental data implies that the approach is considered well-suited for fine-tuning welding and annealing parameters to achieve improved formability in TWBs.