In order to investigate the size dependence of microstructure of the AlSi10Mg alloy fabricated by selective laser melting (SLM) combined with a powder bed technique, plate-shaped AlSi10Mg alloy ...samples with various widths (ranging from approximately 10mm to 0.3mm) were produced in this study. All the fabricated samples exhibited characteristic microstructural morphologies consisting of melt pools with columnar α-Al grains surrounded by fine eutectic Si particles, whereas their sample sizes had a relatively small effect on the texture and average grain size of the α-Al matrix. However, the formation of fine Si precipitates inside the columnar α-Al grains was observed more often for the smaller-sized samples, which could be a possible dominant contributor to the observed softening of the sample by reducing sample size. The obtained results were utilized for discussing the size dependence of the strength of the SLM-manufactured porous alloy samples.
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•Plate-shaped samples with various widths were fabricated via selective laser melting.•The hardness of AlSi10Mg samples slightly decreased with decreasing sample width.•The alloy sample size had a slight effect on microstructure of the α-Al matrix.•Precipitation of Si phase in α-Al matrix was enhanced by reducing the sample size.•The softening by reducing sample size is likely due to their slower cooling rate.
In order to understand the microstructural characteristics of cellular (porous) AlSi10Mg alloy fabricated via selective laser melting (SLM), we designed SLM-fabricated AlSi10Mg alloy samples with ...various box-shaped structures containing interior X-shaped shelves as a representative model of porous aluminum. All fabricated samples exhibited characteristic microstructural morphologies comprising melt pools with columnar α-Al phases surrounded by fine eutectic Si particles. Several columnar α-Al phases exhibited 〈001〉 orientations along the elongation direction, resulting in a {001} texture. In the shelf wall regions of fabricated samples, the elongation direction of the columnar α-Al phases varied depending on the incline angle between the inclined wall plane and the laser irradiation direction (θ), reducing the formation of {001} texture in samples with high incline angles. In the regions wherein the X-shaped shelves intersect, the microstructure varied in different sections: the α-Al phases observed in the lower portion appeared coarser and more equiaxed compared with those in the upper portion. The microstructural difference was more significant in samples with higher incline angles, which contributes to the observed variations in hardness values. Based on the results obtained, we discuss the dominant factor leading to the observed inhomogeneity of the microstructure of cellular AlSi10Mg alloy fabricated via SLM.
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•Various box-shaped samples with X-shaped shelves were fabricated via selective laser melting process.•The elongated direction of α-Al changes as the incline angle of the shelf walls.•Microstructural inhomogeneity was found in the fabricated cellular samples.•The inhomogeneity might be due to the low thermal conductivity of powder.
This study investigated the high-temperature strength of a hypereutectic Al–Fe binary alloy (Al–15%Fe) additive-manufactured by laser powder bed fusion (L-PBF). The L-PBF Al–15%Fe alloy exhibited ...superior yield strength to the other existing L-PBF processed alloys due to α-Al/Al6Fe eutectic structure with a nanoscale cellular morphology. The present results demonstrated the feasibility of using L-PBF processed Al–Fe alloys as high-temperature lightweight materials.
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•Fast scanning calorimetry (FSC) was applied for the solidification of AlSi10Mg powder in a wide range of cooling rates (dT/dt).•Focus ion beam was used for microstructural ...characterization of rapidly solidified AlSi10Mg powder in the FSC equipment.•The secondary dendrite arm spacing (λ) of the primary α-Al phase decreased in the samples solidified at a higher dT/dt.•Extrapolating the relation between λ and dT/dt can estimate the local cooling rate in melt pools of laser additive manufactured Al alloys.
We examined the variation in the solidification microstructure of AlSi10Mg alloy powder over a wide range of cooling rates controlled by using the fast scanning calorimetry (FSC) technique. Two exothermic peaks derived from the primary solidification of the α-Al phases and the α-Al/Si eutectic reaction were detected. These exothermic peaks became broader and shifted to lower temperatures at higher cooling rates. Focus ion beam (FIB) milling enables microstructural characterization of AlSi10Mg powder solidified at controlled cooling rates above 102 °C·s−1 in the FSC equipment. The sample solidified at 4 × 104 °C·s−1 exhibited a fine microstructure consisting of a primary α-Al phase surrounded by lamellar-shaped Si phases. The fraction of the Si phase continuously decreased with increasing cooling rate, indicating higher content of solute Si element in the α-Al phase solidified at a higher cooling rate. The secondary dendrite arm spacing (λ) of the primary α-Al phase decreased in the sample solidified at a higher cooling rate (dT/dt). The relation follows a general equation of λ = A (dT/dt)-n (A: 38.4, n: 0.33) in wide range of cooling rate (10-1 ∼ 104 °C·s−1). The results were utilized to discuss the cooling rate of Al alloys during the laser powder bed fusion (L-PBF) process.
Aluminum alloys fabricated by laser powder bed fusion (L-PBF) exhibit anisotropic tensile ductility. To identify microstructural origins in melt-pool (MP) structures (formed by the l-PBF process) ...contributing to the anisotropic ductility, the local strain distribution inside the MP structure in deformation was quantified by a combination of digital image correlation (DIC) strain analysis and in-situ SEM observations of tensile tests. It was found that higher strain was localized in locally coarsened microstructures (softer regions) along melt-pool boundaries (MPBs). The strain localization played a significant role in crack initiation (and propagation) around MPBs, contributing to fracture. The strain localization at MPBs changed depending on the geometrical relation of the MPBs with the loading direction (LD), which was controlled by the LD with respect to the building direction of l-PBF samples. The three-dimensional MPB distribution related to the LD would be responsible for the anisotropic ductility.
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An attempt was made to additively manufacture an Al–Fe binary alloy sample with a hypereutectic composition of 15 wt% Fe using a laser powder bed fusion (LPBF) process. The LPBF-built Al–15Fe alloy ...sample exhibited a microstructure consisting of a number of melt pools in which regions had locally melted and rapidly solidified due to scanning laser irradiation during the LPBF process. The α-Al (fcc) matrix consists of a number of elongated grains with a mean size of approximately 10 μm. These microstructural features correspond well to previous results of Al alloys additively manufactured by the LPBF process. It was found that relatively coarsened stable θ-Al13Fe4 phases with a length of a few micrometers were localized along the melt pool boundaries. Numerous spherical particles of a metastable Al–Fe intermetallic phase were finely distributed within the nanoscale eutectic microstructure consisting of α-Al and metastable Al6Fe phases inside the melt pools. The metastable phase formation corresponds well to the previous results on the rapidly solidified Al–Fe alloys. The refined multiple intermetallic phases produced by the LPBF process contribute to a high hardness of approximately 200 HV. The refined microstructure appeared stable at an elevated temperature of 300 °C. The high microstructural stability would sustain sufficient strength in a hostile environment for long-term periods of service at elevated temperatures above 200 °C. The present results were utilized to discuss the formation sequence of multiple Al–Fe intermetallic phases in rapid solidification by the LPBF process.
•An Al–15 wt%Fe alloy was additively manufactured by laser powder bed fusion (LPBF).•Microstructure consists of melt pools in which regions locally melted and solidified.•Relatively coarsened Al13Fe4 phases were localized along the melt pool boundaries.•A nanoscale eutectic microstructure of α-Al and metastable Al6Fe phases was found.•Al–Fe intermetallic phases refined by LPBF exhibited high stability at 300°C.
The formation of shear band in metallic lattice structures under compression prompts an unstable stress–strain curve, resulting in a significant reduction in the energy absorption capacity. The ...development and formation of shear band need to be clarified, and versatile approaches to suppress the shear band are required. In this study, we explored the formation mechanism of shear band using a representative Al–12Si alloy lattice structure, consisting of a simple body-centered cubic (BCC) unit cell manufactured by laser powder bed fusion. The X-ray computed tomography observations of an interruptedly compressed lattice specimen and finite element analyses revealed that the crack initiations in the bent struts under the localized tensile stress trigger the formation of shear band. Accordingly, an attempt was made to fabricate various lattice structures consisting of BCC unit cells with different strut diameter ratios to suppress shear band formation. Finite element analyses revealed relaxed tensile stress inside the struts with the controlled diameter ratios, suggesting the suppressed formation of shear bands; this was demonstrated by compression tests. The present results provide new insights for achieving a stable compressive deformation and high energy absorption capacity of lattice structures.
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•Shear band evolution was elucidated using X-ray computed tomography and the finite element method.•Crack initiation caused by tensile stress generated in struts is the conclusive trigger of shear band formation.•Strut shape was numerically optimized to relax the tensile stress generated in struts.•Shear band formation was actually suppressed by optimizing the strut shape.
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Metal additive manufacturing (AM) enables the fabrication of lattice-structured heat sinks with enhanced heat transfer properties. The lattice structural features for enhancing heat ...transfer and suppressing pressure loss need to be clarified. To describe the structural features dominating heat transfer and pressure loss, eleven structural parameters consisting of three groups, namely the area, hydraulic diameter, and effective flow path, are proposed and used as inputs for the neural network (NN) surrogate model. The surrogate model precisely and quickly predicts the heat transfer property and pressure loss simulated by computational fluid dynamics. The random forest feature importance is used to select necessary and sufficient structural features. Four parameters describing the bottleneck in the flow pathway, surface area, and intricate structures are selected. Even when only the selected four parameters are used, the NN model maintains a high prediction performance, suggesting that the four parameters are sufficient for describing the heat transfer and pressure loss. Four parameters are used to discuss the design concept for lattice-structured heat sinks. An appropriately intricate lattice structure exhibits improved heat transfer and reduced pressure loss compared to a simple lattice structure. This study provides new insights into the design of lattice-structured heat sinks fabricated by AM.
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