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.
The precipitation kinetics and mechanisms of 6000 series aluminium alloys (6082 and 6061 alloys) are studied through the changes in the electrical conductivity. This is supplemented by hardness measurements. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) and Austin-Rickett (AR) models are applied to the results of the electrical conductivity measurements carried out on the two aluminum alloys allowing their parameters to be identified. These two models offer a good representation of the precipitation kinetics of the two aluminum alloys. They were also used to calculate the activation energies for the transformations by applying the Arrhenius equation. The activation energies obtained are consistent with the data in the literature. Finally, two partial timetemperatureprecipitation (TTP) diagrams are created for the 6082 and 6061 alloys. A comparison of the information obtained from these diagrams and the Transmission Electron Microscopy (TEM) examinations is proposed for these two aluminium alloys and thus makes it possible to find a good match.
After having determined the LPBF additive manufacturing parameters for the AlSi5Cu3Mg alloy by means of a design of experiment method, three tempers are studied on the manufactured test pieces: as built, direct aging and T6. The study reviews the impact of these three tempers on porosity assessment, microstructure and mechanical properties. It appears that the microstructures in the as built and direct aging tempers are often comparable to those of the AlSi7Mg0.6 and AlSi10Mg alloys which are used as references. However, a significant difference appears with the T6 temper, which does not show any change in porosity for the AlSi5Cu3Mg alloy, unlike the two other alloys. Moreover, due to a high density of type θʺ and/or θ′ fine precipitates, the T6 temper features a high yield strength but also an almost isotropic behaviour with good elongation. The analysis of the mechanical behaviour of the AlSi5Cu3Mg alloy in the three tempers is completed with an analysis of the strain hardening rate which is put into perspective with an EBSD analysis of the dislocation density, thus highlighting a close relationship between the microstructures (especially fine dendritic structures) and a high dislocation density. Lastly, a technical and ergonomic study is presented which compares the AlSi5Cu3Mg and AlSi7Mg0.6 alloys. Finally, we explain the interest of the T6 temper for the AlSi5Cu3Mg alloy after LPBF additive manufacturing.
Warm forming of aluminum is a recent process and its developments have been mainly focused on drawing. This study takes a look at bending, a process widely used in industry. After the 2017A T4 and 6061 T6 aluminum alloys are characterized at both room and warm temperatures, bending of these materials is carried out at different temperatures. Various bending strategies are studied. The findings point to the value for these materials in heating the bend during the forming operation to avoid cracking, in some cases, and to minimize springback. An analysis of the sheet metal distortion mechanism is carried out based on micrographic sections sampled in the bend. The analysis highlights the formation of “macro-bands” indicating the location of the distortion. Asperities are observed on the outer surface. This could be the fracturing site of certain grains located in the grooves of the asperities, with possible intergranular or transgranular cracking. A potential follow-up to this study could be to assess the changes in the mechanical characteristics after the aluminum alloy sheets have cooled to room temperature.
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