Tailoring heat treatment for AlSi7Mg0.6 parts with as-built surface generated by laser powder bed fusion to reduce surface roughness sensitivity

The most important advantage of additive manufacturing by laser powder bed fusion (PBF-LB) technique is the ability to produce geometrically complex parts, but the problem is their rough surfaces, often difficult or inaccessible to finish by machining. Therefore, research to improve the reproducibility of the mechanical behavior of parts manufactured from aluminum alloy powders with as-built surfaces is of vital importance for the aerospace and automotive industries. Since local notches occurring on rough surfaces after the PBF-LB process are unavoidable, the way to solve this problem is to obtain as-built surfaces of the highest possible quality and to adapt a post-process heat treatment that increases the ductility and fracture toughness of the material. To this end, the present work focused on the study of the mechanical performance of AlSi7Mg0.6 samples with a rough as-built surface in the as-built state and after several variants of post-process heat treatment, combined with a detailed analysis of the microstructures corresponding to these states. Tensile samples built on a platform preheated to 100 °C, achieved a relative density of 99.85%, satisfactory surface quality, a relatively low level of residual stress and moderate crystallographic texture. Despite the rough surface, the samples under the as-built condition and after different variants of heat treatment (direct aging (DA), stress relieving (SR), and solution annealing followed by artificial aging (T6)), achieved tensile properties comparable to those reported in the literature for PBF-LB samples with machined surfaces. The resulting combinations of tensile properties of PBF-LB samples after different heat treatment variants were evaluated using the quality index (QI) commonly used to assess the quality of heat-treated Al-Si-Mg castings. It was found that the proposed T6 treatment provides the best combination of strength properties and ductility, compared to those obtained after both DA and SR, as well as after T6 treatment of high-quality castings, from the point of view of reducing the sensitivity of AlSi7Mg0.6 alloy to surface roughness.