This study presents a panorama of the AlSi7Mg0.6 (A357) aluminum alloy in additive manufacturing by selective laser melting. The document is mainly interested in the metallurgical tempers obtained after manufacture and after heat treatment; it quickly cover the process. The results concerning the material integrity (porosity), mechanical properties, microstructures, residual stresses, etc., are presented in order to best define the technological capacities of these metallurgical tempers: as-built, soft annealed, T6, and artificial aging. Some information on the mechanisms and kinetics of precipitation is also presented using the Johnson-Mehl-Avrami-Kolmogorov model. Finally, the conclusion proposes an inventory (advantages/disadvantages) of the metallurgical tempers obtained to better understand the industrial applications.
Samples of AlSi10Mg alloy were first constructed, selecting the manufacturing parameters through a parametric method based on an experimental design; with the same technique, samples of a metallic matrix composite (AlSi10Mg matrix base and particles of SiC reinforcements) were also made. The evolution of the density with the introduction of reinforcements into the AlSi10Mg alloy was studied. This showed an increase in the porosity level with the reinforcement volume fraction. The material hardness and electrical conductivity were then evaluated, along with conventional mechanical characteristics, and microstructural changes with respect to heat treatments on both the AlSi10Mg alloy material and AlSi10Mg matrix composite. Doing so allows correlating material hardness and electrical conductivity (as observed for conventionally produced alloys: casting or wrought). The tensile strength, yield strength and Young's modulus were measured. A significant increase in the conventional mechanical characteristics compared with casting was shown, due to hardening by structure refinement. Evidence is given to relate the yield strength value to the reduction in the dendrite arm spacing (DAS) by application of the Hall-Petch law. We discuss the understanding of the thermal process involved (temperature distribution and fast cooling rate). In addition, observations and analysis of the microstructural changes are presented: building tracks, the disturbed zone, and structural variations linked to heat treatment.
Various selective laser melting (SLM) configurations (8 in all) were tested on aluminum alloy AlSi7Mg0.6 by making single tracks on parallelepipeds specimens. We used an energy balance as a means of connecting the machine parameters (power, speed, etc.) of the 8 configurations to the morphology (geometry) of the single tracks. On this basis, we correlated the width, depth and especially the section area of the melt pool (single track) to the linear energy density. We were also able to assess the absorption coefficient of the aluminum alloy AlSi7Mg0.6 as a function of the temperature. The study was then focused on the microstructure and the possible impacts on the material properties including on the mechanical characteristics and the anisotropy observed in literature based on the build direction. Evidence suggests that the Hall-Petch relation can be used to explain this anisotropy. The thermal analysis highlighted two laser operating modes: the keyhole mode and the conduction mode. These modes have also been described via the morphology of the single tracks. Finally, a comparison between Rosenthal’s theoretical model (in the case of the conduction mode) and actual conditions was proposed by the obtained geometry of the single tracks as well as the cooling speeds calculated and measured using the dendrite arm spacing (DAS). The maximum temperatures achieved were also assessed by Rosenthal’s theoretical model which made it possible to explain the evaporation of some chemical elements during the manufacturing of the aluminum alloy through SLM.
This study presents a panorama of the AlSi7Mg0.6 (A357) aluminum alloy in additive manufacturing by selective laser melting. The document is mainly interested in the metallurgical tempers obtained after manufacture and after heat treatment; it quickly cover the process. The results concerning the material integrity (porosity), mechanical properties, microstructures, residual stresses, etc., are presented in order to best define the technological capacities of these metallurgical tempers: as-built, soft annealed, T6, and artificial aging. Some information on the mechanisms and kinetics of precipitation is also presented using the Johnson-Mehl-Avrami-Kolmogorov model. Finally, the conclusion proposes an inventory (advantages/disadvantages) of the metallurgical tempers obtained to better understand the industrial applications.
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