Finite element modeling of microstructure evolution and bonding during Friction Stir Extrusion of AA6061 powder at different tool feed rates and rotational speeds

Friction Stir Extrusion (FSE) enhances material properties by producing a fine-grained microstructure, offering improved mechanical strength and eliminating the need for melting, thus reducing potential defects and energy consumption. However, the effects of process parameters on these properties are still under investigation by the research and industrial community. The aim of the present work is therefore to propose a methodology that integrates finite element method (FEM) analysis and analytical models to determine and predict the effects of process parameters on the characteristics of profiles extruded through FSE. Two profiles were extruded using AA6061 powder through FSE with different combinations of process parameters: tool rotation speeds of 400 rpm and 1000 rpm, and die feed rates of 3 mm/s and 1 mm/s. The profiles were analyzed experimentally to assess the main differences in terms of surface quality, extrusion force, hardness, and microstructure. Experimental results indicated significant differences in bonding and microstructure across samples processed under different conditions. At a rotational speed of 1000 rpm and feed rate of 1 mm/s, complete bonding occurred early, within the first 5 mm of the die stroke, resulting in a fully consolidated material with equiaxed grains. In contrast, at 400 rpm and 3 mm/s, bonding progressed more gradually, with voids observed in the inner section of the extruded rod. Grain sizes varied accordingly, with finer grains at lower rotational speeds. Numerical simulations performed using Qform UK aligned well with experimental data, accurately predicting bonding initiation and grain size distribution.