Shear texture development and microstructural analysis of friction stir welded AA5754 sheets during forming at different strain paths

Abstract

Modern automotive, marine, and aviation industries seek defect-free Al-Mg alloy welds for uniform strain distribution during complex shaping. Despite this critical need, limited research was done on the formability of friction stir welded blanks. This study aimed to examine the shear texture development and microstructural analysis of friction stir welded AA5754 sheets during forming at different strain paths. It is also sought to correlate the changes ensued before and after deformation with microstructures and formability. Four combinations of rotational speeds (1200 and 1600 rpm) and traverse speeds (90 and 150 mm/min) were used to produce 1.5 mm thick butt-welded AA5754 sheets. Limit Dome Height (LDH) experiments were performed for three different strain paths (uniaxial, plane, and biaxial) to assess the formability in terms of strain path diagram. Strain path curves and von Mises effective strains revealed that plane strain limits were lowest for most parameter combinations, except 1200 rpm - 150 mm/min and a peculiar behavior was observed in the minor strains of biaxial strain paths. The reason for this peculiar behavior was further confirmed by weak or absent texture C in biaxial strain paths and declining pole figure intensities at 1200 rpm - 150 mm/min across the strain paths during shear texture analysis. Grain orientation spread (GOS) maps differentiated deformed and recrystallized regions. The minimum average Taylor factor (M) in the biaxial strain path of deformed base material indicated maximum slip system activation. Moreover, for all the specimens the average M ranged between 3 and 4, which signified that the grains exhibited adequate amount of stress levels and high level of work hardening.