rus
Issue #7/2021
A. D. Eremeev, D. V. Volosevich
Study of the Formation of the Structure of Laser Tracks During Laser Growing From AlSi10Mg Alloy Powder
Study of the Formation of the Structure of Laser Tracks During Laser Growing From AlSi10Mg Alloy Powder
DOI: 10.22184/1993-7296.FRos.2021.15.7.558.566
The article describes a technique for manufacturing technical samples of AlSi10Mg by laser cladding. The effect of structure and defects on the mechanical strength of this alloy was studied at a process productivity of 1 kg / h and 1.5 kg / h. Mechanical tests for the grown samples are presented. With a decrease in the laser radiation power, a decrease in the dendritic cells of the structure from 204 μm to 46 μm was observed. On a sample with enlarged structure cells and the presence of defects, a significant decrease in the mechanical strength of transverse samples was observed.
The article describes a technique for manufacturing technical samples of AlSi10Mg by laser cladding. The effect of structure and defects on the mechanical strength of this alloy was studied at a process productivity of 1 kg / h and 1.5 kg / h. Mechanical tests for the grown samples are presented. With a decrease in the laser radiation power, a decrease in the dendritic cells of the structure from 204 μm to 46 μm was observed. On a sample with enlarged structure cells and the presence of defects, a significant decrease in the mechanical strength of transverse samples was observed.
Теги: additive manufacturing aluminum alloys laser cladding macrostructure аддитивное производство алюминиевые сплавы лазерная наплавка макроструктура
Study of the Formation of the Structure of Laser Tracks During Laser Growing From AlSi10Mg Alloy Powder
A. D. Eremeev, D. V. Volosevich
Saint Petersburg Marine Technical University,
Saint Petersburg, Russia
The article describes a technique for manufacturing technical samples of AlSi10Mg by laser cladding. The effect of structure and defects on the mechanical strength of this alloy was studied at a process productivity of 1 kg / h and 1.5 kg / h. Mechanical tests for the grown samples are presented. With a decrease in the laser radiation power, a decrease in the dendritic cells of the structure from 204 μm to 46 μm was observed. On a sample with enlarged structure cells and the presence of defects, a significant decrease in the mechanical strength of transverse samples was observed.
Key words: additive manufacturing, laser cladding, aluminum alloys, macrostructure
Received on: 07.09.2021
Accepted on: 21.09.2021
Introduction
Various materials are used for additive manufacturing, ranging from plastics [1] and composite materials [2] to a wide range of various metal alloys based on iron, nickel, titanium, including aluminum. Today, aluminum alloys are essential for the additive production of innovative parts in various fields: aerospace technology [3–4], military technology [5], load-bearing elements of automobile bodies [6] and others. Their high significance is associated with the peculiarities of the physicochemical properties of aluminum alloys: high thermal conductivity, low density, plasticity, and corrosion resistance. At the same time, pure aluminum has a low mechanical strength of 80–100 MPa. Therefore, in production, aluminum alloys alloyed with copper, magnesium, silicon, etc. are widely used to increase the strength properties.
One of the widely used materials in additive manufacturing is the aluminum alloy AlSi10Mg. The most common method of cladding this material is selective laser sintering [7–9]. One of the main obstacles to the widespread use of this technology is its relatively low productivity up to 0.1 kg / h, since the time for creating a small model can vary from several hours to several days. The direct laser growth method can significantly increase the productivity of the cladding process, due to the possibility of a larger transfer of material per unit of time (from 1 kg / h and more).
But with an increase in productivity, the likelihood of the appearance of internal defects in the form of pores, lack of fusion and intercrystalline cracks is high. The main task was to find a balance between the productivity of laser cladding of AlSi10Mg aluminum powder and an increase in mechanical properties, due to obtaining an optimal structure and reducing the number of defects.
Experimental technique
Samples of aluminum alloy AlSi10Mg were made on a direct laser growing technological complex (Fig.1.1) consisting of an LS‑3 fiber laser (IPG Photonics, USA) with a power of up to 3 kW with a D‑30L laser head (IPG Photonics, USA) equipped with a four-string nozzle. Positioning and cladding were carried out using a six-axis industrial robot M‑20iB / 25 (Fanuc, Japan).
The cladding of the samples was carried out in a hermetically sealed chamber in an atmosphere of protective gas – argon. AlSi10Mg powder, 63–125 μm fraction was chosen as the cladding material. The composition of the powder and its histogram are presented in Table 1.1 and Fig. 1.2.
The particle size distribution of the powder was 60–200 µm, the powder particles had a spherical shape with a satisfactory surface quality, and the chemical composition corresponded to GOST 1583–93.
In the experiment, two series of samples were carried out with different variation of the mode parameters (Table 1.2).
The series of experiments differed in the productivity of the modes: 1 kg / h and 1.5 kg / h, as well as in different values of the laser radiation power. The cladding was carried out in one pass, with the next layer turning by 180 degrees. The samples were grown sequentially, first the first track for all samples, then the second track for all samples, etc. Height offset between layers 0.8 and 0.6 mm. Pause between adjacent tracks 15 s. The size of the standard sample is shown in Fig. 1.3.
The samples obtained in the course of the study were examined in cross-section using a Leica DMi8 metallographic microscope (Leica Microsystems, Germany), designed to control the quality of metals. The following was chosen as the etching reagent: 50 ml H2O, 1 ml HF, 2 ml HNO3. The etching time was 20 s.
Mechanical tests were carried out on a Zwick Roell Z100 universal testing machine (Zwick Roell, Ulm, Germany), two samples for each direction.
Discussion of the results
Metallographic research
Figures 2.1 and 2.2 show the results of metallographic examination.
The result of the analysis of thin sections showed that the samples of the first series contain pores, in an amount of less than 1% of the sectional area of the thin sections. In the samples of the second series, in addition to pores, which are up to 5% of the cross-sectional area, lack of fusion and intercrystalline cracks are present.
After the analysis of defects, images of the macrostructure were obtained for the samples of the first series and sample No. 2.2 of the second series (Fig. 2.3).
2.2. Macrostructure
Fig. 2.3 shows optical micrographs of cross-sections of cladding specimens of the first series and specimen No. 2.2 from the second series. The samples demonstrate a structure typical for hypoeutectic alloys of the Al-Si system, containing, as can be seen from Fig. 2.4, primary α-Al and Al-Si eutectic.
The structure of the specimen has a periodic character: dendrites are formed at the boundary of the laser track, which are then replaced by a fine-cellular structure. The dendritic structures are oriented towards the center of the tracks, and the size of the dendritic regions decreases with increasing laser power and is 145, 82, and 46 μm for the samples of the first series at powers of 1600, 1800, and 2000 W and 228, 184, and 140 μm for the second series, respectively. The predominantly fine cellular structure is equiaxed with a cell size of 1.79; 1.83 and 1.85 microns at powers of 1600, 1800, 2000 W and 5.34; 5.16 and 5.2 μm for the second series.
Such an increase in the cells may be due to the fact that with an increase in the spot and the rate of the process, the energy density decreases, therefore, the temperature gradient decreases. In the upper part of the cladding layers, where the rate of heat removal is higher, cells close to equiaxial formation are observed. The size of the dendritic cells in the structure, e. g., for cast aluminum alloys, plays a significant role in the final properties of the product. The aluminum alloys with a finely dispersed structure show higher mechanical and technological properties in comparison with the coarser structure of the same materials. In addition, the presence of a large number of pores and lack of fusion significantly affects the mechanical properties.
2.3. Mechanical tests
In fig. 2.5 shows an example of specimens grown for mechanical testing. The results of mechanical tests for sample No. 2.2 are shown in Table 2.1 and 2.6.
It can be seen from the results that if in the longitudinal direction the value of strength is approximately similar to casting materials, then the tensile strength of the sample across, the indicators are significantly lower. The reasons for such strength values are the presence of a large number of pores, lack of fusion, the presence of intercrystalline cracks, as well as increased dendritic cells of the structures.
Conclusions
Based on the results of the study, the following conclusions were made:
Experiments on the cladding of technical specimens from AlSi10Mg powder have been carried out. It was found that at a more productive mode of 1 kg / h, intercrystalline cracks and lack of fusion are observed, as well as pores up to 5% of the cross-sectional area of the sample.
Results on the effect of laser radiation power on the formation of a structure during cladding of AlSi10Mg aluminum powder have been obtained. Dependences of the sizes of dendritic cells and their shape on the power of laser radiation have been established.
The analysis of the influence of structures obtained in the process of laser cladding of aluminum powders on the mechanical properties is carried out. It was found that a decrease in the cells of the dendritic structure has a positive effect on the mechanical properties. Defects found on one of the samples significantly reduced its mechanical properties in comparison with the properties of casting blanks.
Acknowledgements
The research was carried out within the framework of a competition for the best projects of fundamental scientific research carried out by young scientists studying in graduate school. Grant No. 19-38-90267 “Investigation of the formation of the structure of laser tracks during laser growth from AlSi10Mg alloy powder” was carried out with the financial support of the Russian Foundation for Basic Research.
AUTHORS
Eremeev Alexey Dmitrievich, e-mail: Eremeev.ad@mail.ru ; researcher, engineer of Saint Petersburg Marine Technical University (SMTU); www.smtu.ru; Saint Petersburg, Russia. Area of interest: additive technologies, materials science.
ORCID: 0000-0003-1987-769X
Volosevich Darya Vladimirovna, e-mail: dasha.volosevich@mail.ru ; engineer of Saint Petersburg Marine Technical University (SMTU), www.smtu.ru ; Saint Petersburg, Russia. Area of interest: additive technologies, materials science.
ORCID: 0000-0002-2288-2935
CONTRIBUTION OF AUTHORS
Eremeev A.D.: the concept of the experiment and its implementation, analysis of the results; Volosevich D.V.: metallographic studies, macrostructure studies, mechanical tests.
CONFLICT OF INTERESTS
Both authors participated in the writing of the manuscript according to the contribution of each of them to the overall experiment and the analysis of its results. The authors guarantee the originality of the results and declare that there is no conflict of interest.
A. D. Eremeev, D. V. Volosevich
Saint Petersburg Marine Technical University,
Saint Petersburg, Russia
The article describes a technique for manufacturing technical samples of AlSi10Mg by laser cladding. The effect of structure and defects on the mechanical strength of this alloy was studied at a process productivity of 1 kg / h and 1.5 kg / h. Mechanical tests for the grown samples are presented. With a decrease in the laser radiation power, a decrease in the dendritic cells of the structure from 204 μm to 46 μm was observed. On a sample with enlarged structure cells and the presence of defects, a significant decrease in the mechanical strength of transverse samples was observed.
Key words: additive manufacturing, laser cladding, aluminum alloys, macrostructure
Received on: 07.09.2021
Accepted on: 21.09.2021
Introduction
Various materials are used for additive manufacturing, ranging from plastics [1] and composite materials [2] to a wide range of various metal alloys based on iron, nickel, titanium, including aluminum. Today, aluminum alloys are essential for the additive production of innovative parts in various fields: aerospace technology [3–4], military technology [5], load-bearing elements of automobile bodies [6] and others. Their high significance is associated with the peculiarities of the physicochemical properties of aluminum alloys: high thermal conductivity, low density, plasticity, and corrosion resistance. At the same time, pure aluminum has a low mechanical strength of 80–100 MPa. Therefore, in production, aluminum alloys alloyed with copper, magnesium, silicon, etc. are widely used to increase the strength properties.
One of the widely used materials in additive manufacturing is the aluminum alloy AlSi10Mg. The most common method of cladding this material is selective laser sintering [7–9]. One of the main obstacles to the widespread use of this technology is its relatively low productivity up to 0.1 kg / h, since the time for creating a small model can vary from several hours to several days. The direct laser growth method can significantly increase the productivity of the cladding process, due to the possibility of a larger transfer of material per unit of time (from 1 kg / h and more).
But with an increase in productivity, the likelihood of the appearance of internal defects in the form of pores, lack of fusion and intercrystalline cracks is high. The main task was to find a balance between the productivity of laser cladding of AlSi10Mg aluminum powder and an increase in mechanical properties, due to obtaining an optimal structure and reducing the number of defects.
Experimental technique
Samples of aluminum alloy AlSi10Mg were made on a direct laser growing technological complex (Fig.1.1) consisting of an LS‑3 fiber laser (IPG Photonics, USA) with a power of up to 3 kW with a D‑30L laser head (IPG Photonics, USA) equipped with a four-string nozzle. Positioning and cladding were carried out using a six-axis industrial robot M‑20iB / 25 (Fanuc, Japan).
The cladding of the samples was carried out in a hermetically sealed chamber in an atmosphere of protective gas – argon. AlSi10Mg powder, 63–125 μm fraction was chosen as the cladding material. The composition of the powder and its histogram are presented in Table 1.1 and Fig. 1.2.
The particle size distribution of the powder was 60–200 µm, the powder particles had a spherical shape with a satisfactory surface quality, and the chemical composition corresponded to GOST 1583–93.
In the experiment, two series of samples were carried out with different variation of the mode parameters (Table 1.2).
The series of experiments differed in the productivity of the modes: 1 kg / h and 1.5 kg / h, as well as in different values of the laser radiation power. The cladding was carried out in one pass, with the next layer turning by 180 degrees. The samples were grown sequentially, first the first track for all samples, then the second track for all samples, etc. Height offset between layers 0.8 and 0.6 mm. Pause between adjacent tracks 15 s. The size of the standard sample is shown in Fig. 1.3.
The samples obtained in the course of the study were examined in cross-section using a Leica DMi8 metallographic microscope (Leica Microsystems, Germany), designed to control the quality of metals. The following was chosen as the etching reagent: 50 ml H2O, 1 ml HF, 2 ml HNO3. The etching time was 20 s.
Mechanical tests were carried out on a Zwick Roell Z100 universal testing machine (Zwick Roell, Ulm, Germany), two samples for each direction.
Discussion of the results
Metallographic research
Figures 2.1 and 2.2 show the results of metallographic examination.
The result of the analysis of thin sections showed that the samples of the first series contain pores, in an amount of less than 1% of the sectional area of the thin sections. In the samples of the second series, in addition to pores, which are up to 5% of the cross-sectional area, lack of fusion and intercrystalline cracks are present.
After the analysis of defects, images of the macrostructure were obtained for the samples of the first series and sample No. 2.2 of the second series (Fig. 2.3).
2.2. Macrostructure
Fig. 2.3 shows optical micrographs of cross-sections of cladding specimens of the first series and specimen No. 2.2 from the second series. The samples demonstrate a structure typical for hypoeutectic alloys of the Al-Si system, containing, as can be seen from Fig. 2.4, primary α-Al and Al-Si eutectic.
The structure of the specimen has a periodic character: dendrites are formed at the boundary of the laser track, which are then replaced by a fine-cellular structure. The dendritic structures are oriented towards the center of the tracks, and the size of the dendritic regions decreases with increasing laser power and is 145, 82, and 46 μm for the samples of the first series at powers of 1600, 1800, and 2000 W and 228, 184, and 140 μm for the second series, respectively. The predominantly fine cellular structure is equiaxed with a cell size of 1.79; 1.83 and 1.85 microns at powers of 1600, 1800, 2000 W and 5.34; 5.16 and 5.2 μm for the second series.
Such an increase in the cells may be due to the fact that with an increase in the spot and the rate of the process, the energy density decreases, therefore, the temperature gradient decreases. In the upper part of the cladding layers, where the rate of heat removal is higher, cells close to equiaxial formation are observed. The size of the dendritic cells in the structure, e. g., for cast aluminum alloys, plays a significant role in the final properties of the product. The aluminum alloys with a finely dispersed structure show higher mechanical and technological properties in comparison with the coarser structure of the same materials. In addition, the presence of a large number of pores and lack of fusion significantly affects the mechanical properties.
2.3. Mechanical tests
In fig. 2.5 shows an example of specimens grown for mechanical testing. The results of mechanical tests for sample No. 2.2 are shown in Table 2.1 and 2.6.
It can be seen from the results that if in the longitudinal direction the value of strength is approximately similar to casting materials, then the tensile strength of the sample across, the indicators are significantly lower. The reasons for such strength values are the presence of a large number of pores, lack of fusion, the presence of intercrystalline cracks, as well as increased dendritic cells of the structures.
Conclusions
Based on the results of the study, the following conclusions were made:
Experiments on the cladding of technical specimens from AlSi10Mg powder have been carried out. It was found that at a more productive mode of 1 kg / h, intercrystalline cracks and lack of fusion are observed, as well as pores up to 5% of the cross-sectional area of the sample.
Results on the effect of laser radiation power on the formation of a structure during cladding of AlSi10Mg aluminum powder have been obtained. Dependences of the sizes of dendritic cells and their shape on the power of laser radiation have been established.
The analysis of the influence of structures obtained in the process of laser cladding of aluminum powders on the mechanical properties is carried out. It was found that a decrease in the cells of the dendritic structure has a positive effect on the mechanical properties. Defects found on one of the samples significantly reduced its mechanical properties in comparison with the properties of casting blanks.
Acknowledgements
The research was carried out within the framework of a competition for the best projects of fundamental scientific research carried out by young scientists studying in graduate school. Grant No. 19-38-90267 “Investigation of the formation of the structure of laser tracks during laser growth from AlSi10Mg alloy powder” was carried out with the financial support of the Russian Foundation for Basic Research.
AUTHORS
Eremeev Alexey Dmitrievich, e-mail: Eremeev.ad@mail.ru ; researcher, engineer of Saint Petersburg Marine Technical University (SMTU); www.smtu.ru; Saint Petersburg, Russia. Area of interest: additive technologies, materials science.
ORCID: 0000-0003-1987-769X
Volosevich Darya Vladimirovna, e-mail: dasha.volosevich@mail.ru ; engineer of Saint Petersburg Marine Technical University (SMTU), www.smtu.ru ; Saint Petersburg, Russia. Area of interest: additive technologies, materials science.
ORCID: 0000-0002-2288-2935
CONTRIBUTION OF AUTHORS
Eremeev A.D.: the concept of the experiment and its implementation, analysis of the results; Volosevich D.V.: metallographic studies, macrostructure studies, mechanical tests.
CONFLICT OF INTERESTS
Both authors participated in the writing of the manuscript according to the contribution of each of them to the overall experiment and the analysis of its results. The authors guarantee the originality of the results and declare that there is no conflict of interest.
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