Correlation of microstructure, texture, and mechanical properties of friction stir welded Joints of AA7075-T6 plates using a flat tool pin profile

Abstract

This study investigates the influence of square and hexagon tool pin profiles on the butt joint of AA7075-T6 plates through friction stir welding. In contrast to the AA7075-T6 base metal with a grain size of 32.736 μm, both square (4.43 μm) and hexagon (5.79 μm) pin profiles led to a significant reduction in grain size within the stir zone (SZ) of the weld cross-section. The SZ region exhibited a gradient in recrystallization and a notable fraction of high angle grain boundaries, attributed to continuous dynamic recrystallization influenced by variations in temperature and strain rate. Pole figure analysis revealed predominant shear texture elements (B/ B‾ and C) with minor A1*/A2* and A/ A‾, indicating elevated strains within the SZ. Orientation distribution function (ODF) analysis identified recrystallization texture elements such as Goss {110} <001>, cube {001} <101>, and P {011} <112>, along with shear texture components F {111} <112> and rotating cube (H) {001} <110>. Tensile and nanoindentation analyses demonstrated that the weld joint using a square-shaped pin profile exhibited higher strength, elongation, and elastic modulus compared to other weld joints. These findings suggest that the square tool pin geometry enhances material flow and grain refinement during welding, thereby improving the mechanical properties of the joint.