AlSi10Mg Specimens Research Articles

Effect of building orientation and heat treatment on the anisotropic tensile properties of AlSi10Mg fabricated by selective laser melting

In this paper, we investigated the effects of building orientation and heat treatment temperature on the anisotropy of SLM-formed AlSi10Mg specimens. Three different deposition orientations of 0°, 45° and 90° and heat treatment temperatures of 270 °C, 300 °C and 330 °C were used to hold the specimens for 2 h, followed by furnace cooling. The metallographic organization, fracture morphology, grain size and morphology, grain orientation and distribution were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). SEM metallographic shows that the white cell structure is eutectic Si where Si grid-like structure distributes around α-Al dendrites. EBSD results show that all specimens consist of a large number of grains growing along< 001 > direction, which is the preferred orientation. The organizational changes in grain size, distribution and low-angle grain boundaries (LAGBS) caused by orientation and heat treatment were analyzed to confirm the anisotropy of the SLMed AlSi10Mg alloy and to analyze and explain the reasons for the poor plasticity of the 90° orientation. The present results provide new insights into the effects of deposition direction and heat treatment parameters on the microstructure and properties of AlSi10Mg alloy prepared by SLM.

The properties of microarc oxidation coatings installed on AlSi10Mg specimens produced by selective laser melting

This paper examines the properties of coatings produced by microarc oxidation (MAO) on AlSi10Mg alloy specimens, which were obtained by selective laser melting. Two different electrolytes were used to install the coatings: silicate and silicate-phosphate. Modes were used that are recommended for the microarc oxidation of high-silicon aluminium casting alloys. As a result, double-layer coatings of different thicknesses were produced in relatively close timeframes of the MAO process. The thickness, roughness and wear spots were analyzed with the help of a laser interference microscope; the hardness was measured on a microhardness tester; the morphology and the elemental composition of the MAO coatings were analyzed by means of scanning electron microscopy (SEM); an X-ray diffractometer was used for phase analysis. The measurements showed that the coatings produced in the silicate-phosphate electrolyte have higher microhardness, corrosion resistance and specific electrical strength. Based on the results of friction tests and having analyzed the Ffr &ndash; Dr hysteresis loops obtained for reciprocating wear of the specimens, with the friction force Ffr and the travel D being simultaneously measured, the authors established that the wear resistance of the coatings produced in silicate-phosphate electrolyte is ~1.4 times higher than in the case of silicate electrolyte. The conducted study confirmed the efficiency of using silicate-phosphate electrolyte for producing high-quality protective coatings, which applies to almost all parameters. The paper shows that MAO coatings installed on AlSi10Mg alloy specimens produced by selective laser melting offer high performance. Thus, they can be recommended for pilot production of spacecraft components.This research was carried out as part of an assignment of the Ministry of Education&nbsp;and Science of Russia, Subject No.: FSFF-2020-0014.

Fatigue behaviour of notched laser powder bed fusion AlSi10Mg after thermal and mechanical surface post-processing

Laser powder bed fusion (LPBF) as an additive manufacturing technology offers high potential to fabricate parts with complex geometries layer-by-layer. However, these parts have inhomogeneous microstructure and very poor surface quality in their as-built condition. The presence of high surface irregularities especially in the downskin surfaces is a challenging issue that can directly influence their mechanical performance especially under fatigue loading conditions. Hence, applying post-treatments to modulate these imperfections can play a critical role. In this study, the individual and hybrid effects of different post-treatments including T6 heat treatment and shot peening on microstructure, mechanical properties and fatigue behaviour of LPBF V-notched AlSi10Mg specimens were investigated. Two different shot peening processes were applied on both as-built and heat treated specimens using steel and ceramic shots with different Almen intensity, shot diameter and shot hardness. The specimens were comprehensively characterized in terms of microstructural features, surface morphology and surface roughness. Mechanical properties including microhardness and residual stresses were measured and fatigue behaviour of the specimens was determined using a stair-case method; fracture surfaces were also critically analyzed. The results of the analysis performed both on the smooth section and the notched section (including notch root, up and down skin areas) indicated the importance of the choice of shot peening parameters with respect to the target geometry and its material properties. In this case, the shot peening treatment with smaller media and lower intensity was more efficient in terms of surface modification and homogenization especially in the downskin surfaces leading to higher fatigue strength. The significant finding of this study is that by pairing the heat treatment and shot peening, the effect of the presence of the notch can be masked obtaining almost the same fatigue strength for the notched specimens as the un-notched counterparts.

Very high cycle fatigue (VHCF) response of additively manufactured materials: A review

AbstractRecently, the diffusion of components produced through additive manufacturing (AM) processes has significantly increased. Concurrently, to ensure the safe employment of AM components, the research has focused on the assessment of their fatigue response. In the present paper, a comprehensive literature review on the very high cycle fatigue (VHCF) response of materials produced through AM processes is provided. The experimental results on the VHCF response of Ti6Al4V, AlSi10Mg, AlSi7Mg, AlSi12, IN718, and 316L specimens produced through different AM processes are summarized. The main factors affecting the VHCF response of AM materials are finally compared and critically analyzed.

A hybrid framework to estimate the surface state and fatigue performance of laser powder bed fusion materials after shot peening

Despite the rapid growth of additive manufacturing (AM) technologies, AM parts usually present relatively poor surface quality in as-built condition. This necessitates the application of customized post surface treatments to efficiently enhance the surface quality and alleviate the adverse effects of high surface roughness and extremely irregular surface morphology on fatigue strength of AM metallic materials. In this paper, starting from an as-built AM surface, a detailed numerical model is developed to effectively estimate the surface morphology of laser powder bed fusion (LPBF) AlSi10Mg specimens after shot peening. The obtained results are then incorporated into two analytical approaches to evaluate the fatigue strength of different series. The accuracy of the model is validated by comparisons made with experimental data obtained considering as-built and shot peened specimens both before and after heat treatment. The results demonstrate that the proposed hybrid approach can serve as a powerful package not only to determine the beneficial contribution of shot peening on the surface morphology of AM material but also to provide an accurate and rather reliable approximation of their fatigue strength.

Influence of heat treatment on the high-cycle fatigue properties and fatigue damage mechanism of selective laser melted AlSi10Mg alloy

The high-cycle fatigue properties and fatigue damage mechanism of AlSi10Mg alloy manufactured by selective laser melting (SLM) were investigated. The influence of the post-heat treatment on the microstructure and high-cycle fatigue properties was also examined. The SLM-manufactured AlSi10Mg alloy was heat-treated under two different conditions, namely T6 and direct aging (DA). The results of the high-cycle fatigue tests, which were carried out at room temperature, imply that, under all three conditions (as-built, T6, DA), the fatigue strength decreases as the number of cycles increases along with the estimated endurance limit. Predominantly, the fatigue properties were influenced by the morphology and size of the Si particles, both controlled by adjusting the heat treatment. The alloy that was processed using DA heat treatment had superior fatigue properties due to its cellular structural morphology characterized by a significant amount of fine Si precipitates. Compared with the as-built and T6 specimens, the superior fatigue limit of the DA alloy is attributable to its outstanding strength characteristics. The reliability of the fatigue life of the DA alloy is relatively high. Fatigue fracture samples revealed that the DA alloy had evenly distributed dislocations along the cellular boundaries. The fine Si particles were found to play an important role in preventing fatigue crack propagation, thereby enhancing fatigue properties. The effect of the heat treatment on the microstructure and mechanical properties of the SLM AlSi10Mg specimens was investigated with a specific focus on fatigue strength. The results highlighted that an appropriate DA process could significantly enhance the fatigue performance of the AlSi10Mg alloy under investigation. The resulting characteristics are highly advantageous and are superior to those obtained with other conventional heat treatment processes.

Influence of heat treatments on AlSi10Mg specimens manufactured with different laser powder bed fusion machines

Mechanical properties such as ultimate tensile strength, yield strength, and tensile elongation of parts manufactured with Laser Powder Bed Fusion (L-PBF) can differ significantly after the building process limiting the advantage of production flexibility of that technology. At this background, the present work investigated the influence of post process heat treatments (HT) on microstructure, hardness, and tensile properties of AlSi10Mg specimens in different As-built (AB) conditions. For this purpose, two superordinate aspects were covered within this study. Firstly, various HTs were performed on specimens built-up with the same L-PBF machine applying the same parameter set-up. Results of tensile tests and hardness measurements were discussed considering the microstructural changes examined with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy as well as X-ray diffraction, and gathered in a material data map. Based on the observed microstructural changes and a calculated quality index which comprises strength and ductility properties, three HTs were selected for the second part of this work. Therein, the effect of these HTs on specimens fabricated with overall three L-PBF machines working with different raw materials, process parameters, and build-up strategies was studied. Specimens characterization included porosity measurements, the evaluation of material defects, microstructure analysis via SEM, hardness measurements, and tensile tests. It was found that strength properties in the AB condition revealed appreciable deviations: Values of yield strength and ultimate tensile strength were from 228 to 292 MPa and from 346 to 484 MPa, respectively. Whereas heat treated specimens at 300 °C for 0.5 as well as 2 h only exhibited slight differences in strength, a complete homogenization of strength properties was obtained after conducting a T6 HT. Nevertheless, ductility was not homogenized after heat treating caused by the presence of material defects such as keyhole pores and lack of fusion defects. It was shown that even slight differences in porosity determined in cross-sections can significantly affect ductility properties.

Effects of Processing Parameters of Selective Laser Melting Process on Thermal Conductivity of AlSi10Mg Alloy.

Selected laser melting (SLM) is a representative process of powder-bed type 3D printing technology that is used to manipulate metals and it generally results in various structural properties according to the process conditions. In this study, a thermal conductivity test was conducted on AlSi10Mg specimens that were manufactured using the SLM process to investigate the influence of various process conditions on the thermophysical characteristics and cellular microstructure of the samples. The building direction of the specimen, laser scan speed, and hatch spacing were considered as process variables, and the thermal conductivity was analyzed for each process variable. In the test results, as the polar angle of the specimen increased from 0° to 90°, the thermal conductivity increased. Furthermore, the thermal conductivity gradually decreased as the scan speed and hatch spacing increased. The differences in thermal characteristics are discussed in connection with the microstructure of the cells constituting the melt pool. The solidified melt pool that formed by the laser beam is composed of cells consisting of an Al matrix and a surrounding Si-rich area. The differences in thermal conductivity of the overall specimens are explained based on the variations in thermal conductivity and cell shape and size for each chemical component.

Fabrication defects and limitations of AlSi10Mg lattice structures manufactured by selective laser melting

Additive manufacturing has enabled the production of lattice structures with tailored mechanical properties. However, process limitations still exist, affecting the quality of the struts, practically limiting sizes and types of printable unit cells. Typically, long, thin, unsupported horizontal struts exhibit large deviations from ideal geometries, due to high surface roughness and internal porosity. AlSi10Mg specimens were designed and fabricated by laser powder bed fusion to investigate the role of strut orientation, size, and overhang length using different sets of process parameters. Visual inspection, three-dimensional scanning, and metallographic inspection of the cross-sections were performed. A quality control methodology based on dimensional and geometric tolerances has been defined in order to quantitatively characterize the quality of the struts. Optimized process parameters were selected and used to fabricate octet-truss specimens which were then characterized by compression testing.

Evolution of internal pores within AlSi10Mg manufactured by laser powder bed fusion under tension: As-built and heat treated conditions

The optimisation of processing parameters to produce high densification AlSi10Mg parts by laser powder bed fusion (LPBF) has received considerable attention in recent years. Nonetheless, it is important to consider the potential presence of as-built large pores in real world applications, e.g. due to limitations of the available LPBF system, time and cost constraints associated with producing near-perfect density and so on. In this work, recycled powder was used to fabricate AlSi10Mg specimens with sub-optimal densification by LPBF and an experimental investigation into the evolution of specimen porosity occurring under increasing tensile load was performed. A combination of high-resolution X-ray micro computed tomography (XμCT) and an in-situ micro-testing stage was employed to acquire 3D images at different loading stages. Specimens were tested in the as-built condition and following hot isostatic pressing (HIPping) or HIPping with T6. As-built porosity did not change markedly in the lead-up to brittle-like fracture. Pores within ductile HIPped specimens were uniformly elongated up to the onset of damage propagation and pore coalescence. Pore shape change occurred largely without volume change at small extension. HIPping plus T6 produced a compromise between as-built and HIPped conditions in terms of the extent of pore modification observed prior to failure.

The Interplay of Geometric Defects and Porosity on the Mechanical Behavior of Additively Manufactured Components

Additive manufacturing (AM) is becoming increasingly popular, but standards for critical defect sizes and porosity levels have not been fully established. The wide range of flexibility offered by AM is unable to be exploited by designers if they do not have confidence in their components’ mechanical behavior. The goal of this study was to understand how the factors of specimen geometry, geometric defects, porosity, and base material ductility impact the performance of realistic AM exemplar components. Geometric defects, including quarter cracks, internal voids, and through holes, were intentionally manufactured into thin-walled, tapered SS 316L and AlSi10Mg AM components. Two levels of porosity were introduced by reducing the laser power in the AlSi10Mg specimens to observe interactions of porosity and the larger-scale geometric defects. Many such components were manufactured, and each component was loaded to failure. Intentionally manufactured defects decreased the failure load and displacement-to-failure for both materials. Geometric defects had a greater effect in the less ductile materials. Increasing the porosity in the AlSi10Mg above a threshold led to density-dominated component behavior, with little impact of intentional large-scale geometric defects. This work demonstrated the interactions between the flaw types and the dependence of the AM component behavior based on inherent material ductility, porosity, and presence of geometric defects. The results from this study provide valuable insight for establishing a critical porosity-defect relationship for AM metals. It also demonstrates that predicting component behavior in AM metals requires an understanding of flaws types and material properties.

Investigation on Correlation between Microstructure and Mechanical Properties of Alsi10Mg Specimens by AM Technology

Investigation on Correlation between Microstructure and Mechanical Properties of Alsi10Mg Specimens by AM Technology

Microstructure and wear characterization of carbon nanotubes (CNTs) reinforced aluminum matrix nanocomposites manufactured using selective laser melting

Aluminum matrix composites are attractive in aerospace and automobile industry due to its low density, high strength and high corrosion resistance. Additive manufacturing methods such as selective laser melting enable the fabrication of such composites with a complex geometry, and the processing of novel, customized, tailored hybrid materials with unique hierarchical microstructures across multiple length scales. However, the microstructure evolution, wear resistance, frictional behavior under different fabrication and operation conditions of such composites still need to be explored. This study aims to fill the research gap in microstructure evolution and wear characterization of SLM-produced CNTs reinforced aluminum matrix nanocomposites. The surface characteristics, density, wear groove morphology, and surface damages in wear tests were examined. It was determined with SEM/EDS that the major phases of SLM-processed CNTs/Al-based nanocomposites were Al9Si and Si. These phases formed during the SLM process within the composites changed their wear behavior drastically. The wear surfaces were undergoing severe plastic deformation and progressive pitting. The wear rate of CNTs/AlSi10Mg nanocomposites specimens is about 33% lower than that of AlSi10Mg specimens. The higher wear resistance of the CNTs/AlSi10Mg nanocomposites specimens with shallow and narrow wear groove is attributed to the CNTs reinforcement induced higher surface hardness and also the unique hierarchical microstructure of the nanocomposites. The results showed that the SLM-produced CNTs reinforced aluminum matrix nanocomposites have good potentials to be an alternative to pure AlSi10Mg counterparts in terms of hardness, strength, frictional and wear behavior.

Effect of processing parameters on overhanging surface roughness during laser powder bed fusion of AlSi10Mg

Abstract It is often required to add a support structure for overhanging surface in additive manufacturing (AM), especially during laser powder bed fusion (LPBF), which has a considerable impact on the promotion and wide application of this technique. The aim of this study is to evaluate the influence of process parameters on the overhanging surface roughness of AlSi10Mg specimens without a support structure under different build angles, 30°, 45° and 60°, respectively. A design of experiment (DoE) approach was adopted to clarify the correlations between the overhanging surface roughness and the causative the process parameters such as contour laser power, contour scanning speed, infill laser power, infill scanning speed and infill scanning angle. The results showed that the influence of each process parameter on the overhanging surface roughness varies with the change in build angle. Above all, the dominant factor was the contour scanning speed. The results of the comparison show that the contour process parameters are much more influential than the infill process parameters. In addition, the process parameters affected the overhanging surface roughness were on the decrease as the build angle increases. When the build angle was 30°, it was necessary to comprehensively consider the influence of infill scanning angle, contour scanning speed and infill scanning speed to obtain a smooth overhanging surface with a low roughness. However, as the build angle increased to 60°, only the contour scanning speed had a highly significant impact. The results also revealed that apart from the contour scanning speed, the interaction between contour scanning speed and contour laser power should be given priority when the build angle is 30° or less. The lowest roughnesses of overhanging surface with build angles of 30°, 45° and 60° were 10.9 μm, 7.9 μm and 4.22 μm, respectively.

Effect of build orientation on fracture behaviour of AlSi10Mg produced by selective laser melting

PurposeA key challenge found in additive manufacturing is the difficulty to produce components with replicable microstructure and mechanical performance in distinct orientations. This study aims to investigate the influence of build orientation on the fracture toughness of additively manufactured AlSi10Mg specimens.Design/methodology/approachThe AlSi10Mg specimens were manufactured using the selective laser melting (SLM) technology. The fracture toughness was experimentally determined (under ASTM E399-09) using C(T) specimens manufactured in different orientations. The microstructure of the specimens was examined using metallography to determine the effects of grain orientation on fracture toughness.FindingsThe fracture toughness magnitude of manufactured specimens ranged between 36 and 50 MPam, which closely matched conventional bulk material and literature values regarding AlSi10Mg components. The C(T) specimens printed in the T-L orientation yielded the highest fracture toughness. The grain orientation and fracture toughness values confirm the anisotropic nature of SLM parts where the T-L-oriented specimen obtained the highest KIC value. A clear interaction between the melt pool boundaries and micro-slipping during the loading application was observed.Originality/valueThe novelty of this paper consists in elucidating the relationship between grain orientation and fracture toughness of additively manufactured AlSi10Mg specimens because of the anisotropy generated by the different melting pool boundaries and orientations in SLM. The findings show that melt pool boundaries can behave as easier pathways for cracks to propagate and subsequently reduce the fracture toughness of specimens with cracks perpendicular to the build direction.

Crack initiation behavior and fatigue performance up to very-high-cycle regime of AlSi10Mg fabricated by selective laser melting with two powder sizes

The high-cycle and very-high-cycle fatigue (VHCF) behavior of AlSi10Mg specimens manufactured by selective laser melting with different printing powder sizes was investigated. The specimens with 20 μm powder size contained more defects than those with 50 μm powder size, and the latter have a higher fatigue property than the former. Unmelted powders were detected as the main source of crack initiation. The specimens printed with 50 μm powder size are more likely to feature subsurface crack initiation in the VHCF regime. Five different types of crack initiation modes were identified, and the fatigue strength was assessed by statistical model.

Machine-learning assisted laser powder bed fusion process optimization for AlSi10Mg: New microstructure description indices and fracture mechanisms

In this study, a machine-learning approach based on Gaussian process regression was developed to identify the optimized processing window for laser powder bed fusion (LPBF). Using this method, we found a new and much larger optimized LPBF processing window than was known before for manufacturing fully dense AlSi10Mg samples (i.e., relative density ≥ 99%). The newly determined optimized processing parameters (e.g., laser power and scan speed) made it possible to achieve previously unattainable combinations of high strength and ductility. The results showed that although the AlSi10Mg specimens exhibited similar Al-Si eutectic microstructures (e.g., cell structures in fine and coarse grains), they displayed large difference in their mechanical properties including hardness (118 - 137 HV 10), ultimate tensile strength (297 - 389 MPa), elongation to failure (6.3 - 10.3%), and fracture toughness (9.9 - 12.7 kJ/m2). The underlying reason was attributed to the subtle microstructural differences that were further revealed using two newly defined morphology indices (i.e., dimensional-scale index Id and shape index Is) based on several key microstructural features obtained from scanning electron microscopy images. It was found that in addition to grain structure, the sub-grain cell size and cell boundary morphology of the LPBF fabricated AlSi10Mg also strongly affected the mechanical properties of the material. The method established in this study can be readily applied to the LPBF process optimization and mechanical properties manipulation of other widely used metals and alloys or newly designed materials.

Machine-Learning Assisted Laser Powder Bed Fusion Process Optimization for AlSi10mg: New Microstructure Description Indices and Fracture Mechanisms

In this study, a machine-learning approach based on Gaussian process regression was developed to identify the optimized processing window for laser powder bed fusion (LPBF). Using this method, we found a new and much larger optimized LPBF processing window than was known before for manufacturing fully dense AlSi10Mg samples (i.e., relative density ≥ 99%). The newly determined optimized processing parameters (e.g., laser power and scan speed) made it possible to achieve previously unattainable combinations of high strength and ductility. The results showed that although the AlSi10Mg specimens exhibited similar Al-Si eutectic microstructures (e.g., cell structures in fine and coarse grains), they displayed large difference in their mechanical properties including hardness (118 - 137 HV 10), ultimate tensile strength (297 - 389 MPa), elongation to failure (6.3 - 10.3%), and fracture toughness (9.9 - 12.7 kJ/m 2 ). The underlying reason was attributed to the subtle microstructural differences that were further revealed using two newly defined morphology indices (i.e., dimensional-scale index I d and shape index I s ) based on several key microstructural features obtained from scanning electron microscopy images. It was found that in addition to grain structure, the sub-grain cell size and cell boundary morphology of the LPBF fabricated AlSi10Mg also strongly affected the mechanical properties of the material. The method established in this study can be readily applied to the LPBF process optimization and mechanical properties manipulation of other widely used metals and alloys or newly designed materials.

An experimental investigation on energy-effective additive manufacturing of aluminum parts via process parameter selection

This paper investigates the influences of process parameters on part quality, electrical energy consumption, and corresponding energy effectiveness (EE) of AlSi10Mg specimens fabricated by selective laser melting (SLM). Here, EE is defined as the ratio between equivalent quality and specific energy consumption (SEC), where SEC refers to the energy consumption per kilogram of part produced during the building process. The reduction of electrical energy without significantly compromising quality via process parameter configuration was studied. Three parameters, laser power, scan speed and overlap rate, were selected and full factorial design was employed. Single track and single layer experiments were conducted to determine the ranges of process parameters, and multiple layer specimens were prepared for the testing of quality performances, including density, tensile strength, and hardness. The energy consumption of the auxiliary system and laser of the SLM machine were measured for SEC calculation. Results show that the density does not increase with increased SEC, while the tensile strength and hardness show increasing trends. EE can be improved without significantly sacrificing density and hardness, but the tensile strength will be greatly reduced. A case showed that a significant percentage (27.8%) of electrical energy could be saved while satisfying the quality requirements via proper selection of process parameters for the manufacturing of SLMed parts. The findings will help process designers to foster the sustainability of additive manufacturing.

Acoustic emission descriptors for the mechanical behavior of selective laser melted samples: An innovative approach

Three different groups of AlSi10Mg specimens are built using Selective Laser Melting (SLM) technique. Each of these groups represents the orientation of the specimens with respect to the building plane. The mechanical characteristics of the specimens are evaluated under uniaxial tensile loading. The Acoustic Emission (AE) technique is used for characterizing the failure modes of the specimens under the uniaxial loading. An innovative parameter, the slope coefficient bAE, is formulated for directly relating the different failure modes in the tested specimens with the acoustic results. The slope coefficient bAE proves to be a powerful tool for understanding the damage characteristics of the specimens. In addition to that, the AE signals are recorded during the tests and are analysed in the Hilbert Spectrum. The signals are first decomposed using Empirical Mode Decomposition (EMD) and then reconstructed after removing the noise. The instantaneous frequencies obtained from the Hilbert Spectrum of the reconstructed signals are used for analysing the damage modes. From the results obtained, it is safe to say that the AE technique is powerful for characterizing the failure modes in materials during their entire loading history.