Microstructural evolution and mechanical properties in thixoformed Al–Si–Cu–Mg alloy: An EBSD-based study

Thixoforming process is an advanced semisolid metal processing (SSM) technique with significant potential to enhance the mechanical performance of structural components. While it offers benefit through grain refinement, the process introduces localized shear-induced strain, microsegregation, and microstructural non uniformity. This study evaluates an Al–Si–Cu–Mg alloy produced by gravity casting (GC), thixoforming (Thixo), and thixoforming with T6 treatment (Thixo-T6). Microstructures were characterised by optical microscopy (OM) for overall grain morphology and electron backscatter diffraction (EBSD) for quantitative grain size, grain-boundary misorientation, and crystallographic texture. The results show remarkable grain refining primary α-Al in Thixo alloy, changing from an anisotropic dendritic network to a fine, equiaxed, and more isotropic globular structure. The local misorientation reported high Kernel Average Misorientation (KAM ≥1.5°) after the thixoforming as the result from the semi-solid shear and spheroidisation form in high fraction of low angle grain boundary (LAGB) subgrains and strain dislocation that produce lattice curvature, accordingly, which improved from 1.1 % in GC and 8.3 % in Thixo alloy. High geometrically necessary dislocations (GND) density was attained after thixoforming and generate more resistance to plastic flow. In addition, X-ray diffraction (XRD) identifies Al 2 Cu-series precipitates consistent with precipitation hardening as the source of the additional T6 strength. Subsequently, the mechanical strength properties are governed by Hall–Petch grain refinement and plastic deformation effect and remarkably improved by 86 % of yield stress (YS) and 61 % ultimate tensile strength (UTS), respectively with the resulting values of 225 MPa and 271 MPa.