Mechanisms of Σ3 Grain Boundary Formation in Laser Powder Bed Fusion-Produced AlSi10Mg Alloy Processed by Twist ECAP

Grain boundaries affect the mechanical and functional properties of crystalline materials by influencing interfacial energy, mobility, segregation, and the accumulation of damage. Among the grain boundaries in the grain boundary network, coincidence site lattice boundaries form a particular type of special grain boundary that is characterized by a higher degree of lattice-site coincidence. The present study examined the mechanisms involved in the formation of grain boundaries in a laser-powder-bed-fused AlSi10Mg alloy which had been subjected to two-pass twist equal-channel angular pressing (twist-ECAP). The microstructural evolution, deformation texture, and local orientation gradients were investigated using electron backscatter diffraction (EBSD). Moreover, atomistic simulations were carried out in order to assess the effect of geometrically necessary boundary (GNB)-like dislocation walls on the retention of planar faults. The EBSD results indicated that twist-ECAP considerably refined the microstructure and produced a strong fiber texture. Most of the Σ3 grain boundary segments detected were found in areas dominated by the ⟨110⟩||ED component, showing that their appearance is strongly dependent on the texture. Also, the atomistic modelling showed that the presence of a GNB-like wall led to the retention of planar-fault configurations and thus resulted in the highest number of atomic environments related to faults and extended dislocation-line lengths. These results show that the formation of Σ3 grain boundary segments in severely deformed LPBF AlSi10Mg is a coupled process which is mainly controlled by macroscopic texture selection and is locally assisted by deformation-boundary evolution.