Heterogeneity consequences on the mechanical and microstructural evolution of an AlSi11Cu alloy obtained by selective laser melting

Abstract An AlSi11Cu alloy was obtained by additive manufacturing (AM) using powder bed fusion by selective laser melting (SLM) from powders with a mean particle size of 40 μm. The printed alloy presented abnormal melting pools (MPs) sizes distribution described by a double fit of a normal logarithmic function that allowed the identification of two groups of melting pools with mean values of 150 μm and 320 μm. The mechanical properties indicated yield strengths between 370 MPa and 390 MPa, depending on the measurement direction. The radial direction showed the best strength and ductility while the transverse direction the worst behavior. Digital image correlation (DIC) analyzes demonstrated multiple strain concentration points in the tensile specimens and more significant strain acceleration for the longitudinal than the radial direction. The alloy's microstructure indicated the formation of columnar grains surrounded by small equiaxed grains describing an abnormal grain growth behavior. The material texture indicated a preferential orientation towards 〈001〉 ‖ to the building direction (BD), with the Cube and Goss texture components as the most intense. The abnormal behavior in the melting pools and the grain size allowed to observe that the largest grain growths were localized in the wider and deeper melting pools. The grain size abnormality and the preferred texture was also reflected in geometrically necessary dislocations (GNDs) density. The highest GNDs were found in the largest columnar grains, preferably oriented towards the direction, while the lowest densities were grouped in the smaller equiaxed grains with random orientation. The radial direction's better mechanical response was due to higher numbers of plastic gradients' formation than in the longitudinal direction and the perpendicular orientation of the melting pools concerning the load direction. Therefore, radial oriented material fracture throughout the melting pools instead of the melting pool boundaries.