The combination of refined microstructures (induced by rapid cooling) and melt pool-induced mesostructures in AlSi10Mg fabricated using laser powder bed fusion (LPBF) – a widely used additive ...manufacturing technique – impart high strength and fracture toughness. Further exploitation of such property combinations requires a detailed understanding of how the processing conditions control the micro- and mesostructures and, in turn, the mechanical performance, especially regarding fracture resistance. Towards this end, the crack resistance curve (R-curve) behavior in different orientations of LPBF-fabricated AlSi10Mg alloys processed with different layer thickness, hatch spacing, and scan strategies was evaluated and correlated with micro- and mesostructural features such as grain size and grain orientation, texture, cell morphology, and melt pool arrangement. Results show a strong anisotropy in both tensile stress-strain behavior and fracture toughness with layer thickness and hatch spacing controlling strength and scan strategy dictating fracture resistance. In terms of tensile stress-strain behavior, the arrangement of melt pool boundaries with respect to loading direction results in anisotropy in ductility whereas strength is controlled by grain size and cellular structure. In case of fracture toughness, measurements show that failure is dominated primarily by melt pool morphology and hence the mesostructure that is controlled by scan strategy. They furthermore reveal, that, despite the pronounced anisotropy in the R-curve behavior the presence of such mesostructure enables a level of damage-tolerance in AlSi10Mg that cannot be achieved in a cast alloy.
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Selective laser melting (SLM) is widely gaining popularity as an alternative manufacturing technique for complex and customized parts. SLM is a near net shape process with minimal post processing ...machining required dependent upon final application. The fact that SLM produces little waste and enables more optimal designs also raises opportunities for environmental advantages. The use of aluminium (Al) alloys in SLM is still quite limited due to difficulties in processing that result in parts with high degrees of porosity. However, Al alloys are favoured in many high-end applications for their exceptional strength and stiffness to weight ratio meaning that they are extensively used in the automotive and aerospace industries. This study investigates the windows of parameters required to produce high density parts from AlSi10Mg alloy using selective laser melting. A compromise between the different parameters and scan strategies was achieved and used to produce parts achieving a density of 99.8%.
•Refined and homogenized cell structure was obtained after direct aging.•No obvious grain growth was observed after aging treatment.•Strength along building direction was significantly improved after ...aging.•The growth of defects was related to the formation of high energy zones.
For additive manufactured aluminum alloys, the inferior mechanical properties along the building direction have been a serious weakness. In this study, an optimized heat treatment was developed as a simple and effective solution. The effects of direct aging on microstructure and mechanical properties along the building direction of AlSi10Mg samples produced via selective laser melting (SLM) were investigated. The results showed that, compared with the conventional heat treatment at elevated temperatures, direct aging at temperatures of 130–190 °C could retain the fine grain microstructure of SLM samples and promote further precipitation of Si phase, however, the growth of pores occurred during direct aging. With increasing aging temperature, while finer cell structures were obtained, more and larger pores were developed, resulting in decreased density of the samples. Two types of pore formation mechanisms were identified. Considering the balance between the refinement of cell structure and the growth of pores, aging at 130 °C was determined as the optimized heat treatment for SLM AlSi10Mg samples. The tensile strength along the building direction of the 130 °C aged sample was increased from 403 MPa to 451 MPa, with relatively high elongation of 6.5%.
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•Fatigue properties of additively manufactured (AM) AlSi10Mg are similar to castings.•Oxide-driven porosity is the most common internal defect in the AM parts.•Pores and oxide ...particle size at the part surface control fatigue life.
It is well-known that the fatigue behavior of cast aluminum alloy parts is largely determined by internal defects, particularly pores and inclusions. In this work, it is shown that such imperfections are also present in AlSi10Mg parts produced by selective laser melting, and serve as sites to initiate fatigue cracks. The effect of hatch spacing and building orientation on tensile and fatigue properties was tested. Oxide-driven pores dominate the fatigue resistance of the samples in this work. The larger oxide particles which are associated with crack initiation likely form by oxidation of metal vapor during part manufacture.
The (TiB2+TiC)/AlSi10Mg composite powders with 1.5 wt% nano-TiB2 particles and 1.5 wt% nano-TiC particles were prepared by ball milling. Aluminum matrix composites (AMCs) reinforced by TiB2 and TiC ...were fabricated via SLM with optimal processing parameters. The (TiB2+TiC)/AlSi10Mg composites showed a very high ultimate tensile strength ∼552.4 MP and excellent ductility ∼12%, which is 40.3% and 166.7% higher than that of unreinforced AlSi10Mg, respectively. The effects of TiB2 and TiC nanoparticles on the SLM processability, microstructures, grain size, and crystallographic texture of (TiB2+TiC)/AlSi10Mg composite were systematically investigated to uncover its underlying strengthening mechanisms. The results showed that the addition of 1.5 wt% nano-TiB2 and nano-TiC particles can obtain fine-equiaxed grains, facilitate microstructural homogeneity, and consequently improved mechanical properties of AlSi10Mg alloy. With the addition of TiB2 and TiC nanoparticles, the coarse columnar grains are completely transformed into equiaxed grains and the average grain size decreases from 12.1 μm to 1.5 μm.
The influence of laser power during selective laser melting (SLM) on the grain morphology and texture component in AlSi10Mg alloy has been investigated, using electron backscattered diffraction ...(EBSD). Both equiaxed and columnar grains were observed. The formation of equiaxed grains was attributed to the huge thermal gradient on the border of melt pool and the columnar to equiaxed transition (CET) occurred in front of the columnar grains. The grain size of low laser power sample was found smaller than that of higher ones. A fine pseudoeutectic structure, in which Si existed as fibrous, was observed because of the high cooling rate. This paper, from a new angle, explained the formations of three different zones across the melt pool, which were differentiated by the morphology of Si phase. The three zones correspond to the three temperature zones, which were divided by liquidus and solidus temperature, during the heating by laser beam. The coarse zones are formed by reheating the basic metal to semi-solid state when the temperature is lower than the liquidus temperature but higher than the solidus temperature.
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•The nucleation at the border of melt pool and the columnar to equiaxed transition are responsible for the formation of equiaxed grains.•Fine pseudoeutectic structure was observed in SLMed AlSi10Mg alloy because of the rapid solidification.•The gradient microstructure is caused by the different temperature zones during the heating of laser beam.•Coarse zones are formed by reheating the basic metal to semi-solid state when the temperature is at mushy zone.
•Among AM samples, least creep displacement belongs to as-built material.•Among cast samples, least creep displacement belongs to cast-AC material.•SLM-FC and Cast-FC samples possess the largest ...creep displacement.•Dislocation creep is the dominant mechanism of creep in all materials.•The indentation-derived n-values may not show good agreement with the bulk-scale (uniaxial)tests.
Compared with time-consuming conventional uniaxial tensile/compressive creep experiments, depth-sensing indentation testing is considered a reliable, and convenient testing technique to assess the time-dependent plastic deformation of materials in a reasonable time scale. In the present study, we report the ambient (room) temperature indentation creep properties of additively manufactured (i.e., laser-powder bed fused) and cast AlSi10Mg alloy at as-fabricated and different post-fabrication heat treatment states. The indentation creep testing parameters (i.e., dwell time, peak indentation load, and indenter shape) were optimized to adequately represent the creep response (time-displacement) variations for different material conditions. To this end, dual-stage, constant loading rate followed by constant-load holding, pyramidal indentation experiments were performed at a loading rate of 10 mN/s, a peak load of 200 mN, and a dwell time of 400 s. Besides, electron backscattered diffraction was performed to evaluate the manufacturing process (selective laser melted versus cast)/ post-fabrication heat treatment/ texture/ creep properties relationships for the studied AlSi10Mg alloy. Also, the indentation hardness, indentation strain rate sensitivity, indentation creep exponent, and activation volume were analyzed to study and confirm the mechanism of indentation creep. The calculated high values of creep stress exponents (i.e., >10) are attributed to dislocation-reinforcing particle interaction as the controlling mechanism of the creep which agrees with this assumption that AlSi10Mg is indeed an in-situ metal matrix composite with eutectic silicon as the reinforcing particles.
Laser powder bed fusion (LPBF)-fabricated Al matrix composites reinforced with SiC particles are strongly influenced by SiC particle features. In this study, the microstructural features, mechanical ...properties, and porosity of moderate volume fraction (10 vol%) microscale SiC-particle-reinforced AlSi10Mg composites fabricated by LPBF under different oxidation temperatures of SiC particles were investigated. The results demonstrate that LPBF-deposited SiCp/AlSi10Mg composites mainly exhibited laser track segments in macroscale and fine cellular-like dendrite grains and (Al + Si) eutectic phases within the melt pool on a microscale. The transition layer of MgAl2O4 was present around the SiC particles in the oxidized-SiCp reinforced AlSi10Mg composites. In addition, the pore spatial distribution of the deposited composites using the microcomputed tomography test and the microstructural formation mechanism using Thermal Calc software were also studied. Using the finite element to model the deposited composites, it was found that the stress and strain distribution presented higher values than those without long-stripe precipitation phases in the deposited parts with long-stripe precipitation phases. The LPBF-fabricated oxidized-10 vol% SiCp/AlSi10Mg composite part with a relatively large ultimate tensile strength (∼405.3 MPa), relative density (∼98.89%), compressive strength (∼1046 MPa) and friction coefficient (0.32) were obtained. In particular, the ultimate tensile strength was larger than that of the other reported SiCp/AlSi10Mg composites with similar volume fractions and particle sizes.
•The microstructures and mechanical properties of L-PBF 10 vol% oxidized-micro-scale SiCp/AlSi10Mg composites were studied.•Pores spatial distribution of deposited composites was studied by micro-CT.•Deformation behavior of composites under tensile conditions was performed by finite element modeling.•The reinforcement types and their formation process were discussed.
•The scatter of fatigue strength for AM materials is reduced if data are correlated to the defect size at failure origin.•Δσw for AlSi10Mg and Ti6Al4V obtained by AM are similar to the properties for ...traditional processes.•ΔKth for small cracks and Δσw show a significant increase, after HT or HIP, respect to the AB condition.
The fatigue behavior of metallic materials fabricated via additive manufacturing processes is currently not well understood and it has been the subject of many experimental investigations in recent years. In this paper we carried out a literature review about the fatigue strength of additively manufactured AlSi10Mg and Ti6Al4V, especially in terms of sensitivity to defects and inhomogeneities. The analysis shows that fatigue properties and key variables (heat treatment, defect size) are very similar to the ones of parts obtained with traditional manufacturing processes. These results confirm that defect tolerant design concepts can be adopted also for AM components.
In this study, friction stir processing (FSP) was used to enhance the corrosion properties through local modification of the microstructure of AlSi10Mg alloy fabricated by laser-powder bed fusion ...(L-PBF) technology. The impact of traverse and rotational speeds on the mechanical and electrochemical properties of L-PBF AlSi10Mg was analyzed with different combinations of processing parameters, with rotational speeds ranging from 800 to 1600 rpm and traverse speeds from 100 to 300 mm/min. The experimental results showed that the Si content within the stir zone is dependent on the combined influence of the rotational and traverse speeds, with a lower traverse speed promoting an enhanced grain refinement and a more homogenous Si distribution, indicated by a low LAGBs with a high HAGBs, resulting in the decrease of the hardness value and improvement of the corrosion performance of the processed material. The lowest hardness was found on the samples processed with a traverse speed of 100 mm/min and the best corrosion performance was observed from the samples processed with a rotational speed of 1600 rpm and a traverse speed of 100 mm/min. The results also indicated that the rotational speed showed a major role on the process, with the influence of the traverse speed diminishing when the material is processed at higher rotational speeds.
•FSP promotes grain refinement and eliminates the porosities of the L-PBF AlSi10Mg alloy.•The corrosion properties are influenced by the percentage of Si particles in the stir zone, and decreases with the increase of the traverse speed.•A higher traverse speed in FSP increases the severity of pitting corrosion.•The rotational speed has a governing role on the properties of FSPed samples, while the influence of the traverse speed is more significant at lower rotational speeds.
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