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Characterisation of a novel Sc and Zr modified Al–Mg alloy fabricated by selective laser melting
Materials Letters 196 (2017) 347–350
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Characterisation of a novel Sc and Zr modified Al–Mg alloy fabricated by selective laser melting Yunjia Shi a,b, Paul Rometsch a,c,⇑, Kun Yang a,c, Frank Palm d, Xinhua Wu a,c a
Department of Materials Science and Engineering, Monash University, Clayton, VIC 3800, Australia School of Materials Science and Engineering, Central South University, Changsha 410083, China c Monash Centre for Additive Manufacturing, 11 Normanby Road, Notting Hill, VIC 3168, Australia d Airbus Group Innovations, IC1 Ottobrunn, 81663 Munich, Germany b
a r t i c l e
i n f o
Article history: Received 23 December 2016 Accepted 17 March 2017 Available online 18 March 2017 Keywords: Selective laser melting Metals and alloys Scandium Electrical conductivity Microstructure Nuclear magnetic resonance
a b s t r a c t Correlations between densification, hardness and electrical conductivity were investigated over a wide range of applied volumetric energy densities (E) for an Al–Mg–Sc–Zr alloy fabricated by selective laser melting. It is shown that porosity dominates electrical conductivity in the low E region up to 77 J/ mm3, while the contribution of solute in solution is more significant in the medium–high E region. Reasons for these differences are discussed and a linear relationship between electrical conductivity and densification in the absence of solute effects is presented. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Selective laser melting (SLM) is a rapidly growing additive manufacturing (AM) technology, which has been used for fabricating steel [1], Ti [2–4], Al and Ni alloys [5]. Recently, Sc as an alloying element was introduced to aluminum alloys made by AM [6–8]. Compared with conventional casting alloys, additions of Sc and Zr present strikingly different effects on AM fabricated alloys both in terms of refined microstructures and improved mechanical properties [8]. The extremely rapid solidification rate during SLM allows much more Sc to be placed in solution than predicted by the relevant phase diagram. Normally, any subsequent solution heat treatment and quenching is not able to increase the amount of Sc in solution any further and may even decrease it [8,9]. The highly supersaturated solid solution obtained during SLM solidification provides excellent conditions for the precipitation of Al3(Sc,Zr) particles during ageing. The precipitation strengthening effect caused by these nano–scale coherent L12 phases improves the strength while maintaining good toughness and ductility [7]. The excellent performance of Al–Mg–Sc–Zr alloys in SLM makes them worthy of further investigation. The aim of this work is therefore to provide fundamental insights into the interrelationships ⇑ Corresponding author at: Department of Materials Science and Engineering, Monash University, Clayton, VIC 3800, Australia. E-mail address: [email protected] (P. Rometsch). http://dx.doi.org/10.1016/j.matlet.2017.03.089 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
between laser scanning parameters and solute in solution, precipitation, porosity, hardness, electrical conductivity and microstructure.
2. Experimental The chemical composition of the powder is Al–3.40Mg–1.08Sc– 0.50Mn–0.44Cu–0.23Zr–0.14Si–0.08Fe (wt%). Samples were fabricated on an EOSINT M280 powder bed machine with a laser beam diameter of 100 lm; a hatch distance (h) of 100 lm and a layer thickness (t) of 30 lm. A series of 18 mm 18 mm 10 mm rectangular specimens were fabricated onto an Al substrate using a platform temperature of 35 °C and a bi–directional scan strategy. The laser scanning speed (v) ranged from 800 to 3000 mm/s, and the laser power (P) ranged from 220 to 370 W. In order to evaluate the effect of energy input on the powder deposition process, the applied volumetric energy density (E) was defined by E ¼ P=vht [10,11]. The densification (D) was averaged from three measurements using the Archimedes method [11,12]. The electrical conductivity (EC) of the cross–section was measured using a Foerster SIGMATESTÒD 2.068 eddy current device at room temperature. The Vickers hardness was measured on the same section using a Duramin A300 hardness tester with a 1 kg load. Ageing was performed in a Carbolite air circulation furnace at 300 °C and 500 °C, followed
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by water quenching. Backscattered electron micrographs (BSE) and energy–dispersive X–ray spectroscopy (EDX) were obtained using a JEOL 7001 FEG scanning electron microscope. Additionally, nuclear magnetic resonance (NMR) spectroscopy was used to evaluate the fractions of Sc in solid solution and precipitates on a Bruker300 MHz Ultra Shield solid–state NMR spectrometer. Peak analysis using Dmfit software and NMR methods are described elsewhere [9,10]. 3. Results and discussion Fig. 1a shows the variation in densification and electrical conductivity with energy density for as–fabricated specimens. The increase of electrical conductivity with increasing E correlates extremely well with the densification trend at E < 80 J/mm3. However, the densification reaches a maximum of 99.98% at E = 103 J/ mm3 and then decreases slightly at E = 154 J/mm3, the electrical conductivity increases almost linearly with E from 80 to 154 J/ mm3. Fig. 1b shows a strong linear relationship between EC and densification for specimens with D < 99.5%, suggesting that the porosity level determines the electrical conductivity in this densification range. For almost fully dense materials with D > 99.5%, the EC appears to be dominated by the amount of solute in solution [9,13], with the solute supersaturation decreasing as E increases. In order to test these hypotheses, five samples were selected based on a constant P = 370 W and v varying from 800 to 3000 mm/s (Fig. 2). The electrical conductivity increases monotonically with increasing E (decreasing laser scanning speed) in both the as–fabricated and aged conditions, but the as–fabricated hardness first increases from E = 41 J/mm3 to E = 77 J/mm3, and then decreases again towards E = 154 J/mm3. When E < 77 J/mm3, both
the EC and hardness increase with increasing densification. It should be noted that the hardness error bars (Fig. 2b and c) are larger at D < 99% (higher laser scanning speed) as a result of the irregularly shaped pores formed due to incomplete melting of the powder. Although the density slightly increases when E increases to 103 and 154 J/mm3, the hardness decreases. This decrease in hardness and increase in EC with increasing E from 77 to 154 J/ mm3 suggests that much more heat is placed into melt pools at lower laser scanning speeds, leading to the partitioning of solutes to more coarse non–hardening precipitates, either due to a decreasing solidification rate and/or an increasing over–ageing effect from the thermal cycling. After peak ageing at 300 °C for 12 h (Fig. 2c), the increase in hardness by >50 HV1 means that a significant amount of nano–scale Al3Sc and/or Al3(Sc,Zr) must have precipitated. The concomitant increase in conductivity by 5%IACS is primarily due to the loss of solute from solution. The BSE images in Fig. 3 reveal colonies of both small columnar grains and sub–micron equiaxed grains. For low E, EDX results show some small Si–enriched particles (Point A) and larger/ brighter Cu–enriched particles along the grain boundaries (point B). These particles occur in higher number densities in the equiaxed grain regions. A few diamond–shaped particles (points C and D) are observed for samples with higher energy densities, especially at 154 J/mm3. EDX results show that these particles are rich in both Sc and Zr (point C contains 2.37 wt% Sc and 1.44 wt% Zr, while point D contains 3.31 wt% Sc and 2.22 wt% Zr). Both the morphology and composition of these particles are characteristic of primary Al3(Sc,Zr) particles. With increasing E, both the volume fraction and size of these particles increase. Furthermore, the bright white non–hardening particles generally become coarser and exhibit a more over–aged appearance with increasing energy density (Fig. 3).
Fig. 1. (a) Plots of densification and EC against energy density for as–fabricated specimens, and (b) linear relationship between EC and densification for specimens with D < 99.5%.
Fig. 2. Effects of energy density and corresponding laser scanning speeds at 370 W on (a) densification and porosity by optical microscopy, (b) as–fabricated hardness and EC, and (c) peak aged hardness and EC.
Y. Shi et al. / Materials Letters 196 (2017) 347–350
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Fig. 3. BSE images at E of: (a, b) 51 J/mm3 (2400 mm/s), (c, d) 77 J/mm3 (1600 mm/s), and (e, f) 154 J/mm3 (800 mm/s); (g) NMR spectra for as–fabricated samples with calculated mass fractions of Sc atoms surrounded by Al atoms in solid solution marked beside the peaks; (h) linear fitting correlations of EC vs. densification both after equilibration at 500 °C for up to 72 h and in the as–fabricated condition.
This explanation can be verified by the NMR spectra shown in Fig. 3g, where the peak at 1700 ppm represents Sc atoms dissolved in the Al lattice and surrounded by Al atoms only, while the peak at 1050 ppm represents Sc in Al3Sc precipitates. The fraction of Sc in solution was calculated as the ratio of the area under the Gaussian peak at 1700 ppm relative to the area under the whole spectrum. With increasing E, the fraction of Sc in solid solution gradually decreases. Together with the SEM results, this confirms that the higher conductivity and lower hardness at E = 154 J/mm3 is due to a reduced as–fabricated solute supersaturation from the higher heat input, i.e. more Sc and other solute species have precipitated as coarse particles during SLM (white particles in Fig. 3). Generally, a slow scanning speed of 800 mm/s provides more heat input and more time to form primary and/or over–aged coarse non–hardening precipitates that may occur in this system, e.g. Al3Sc, Al3Zr, Al3(Sc,Zr), Al2CuMg, Mg2Si, Mn–dispersoids or Fe–intermetallics. By contrast, the higher scanning speed of 1600 mm/s leads to a faster solidification cooling rate well in excess of 1000 K/s [8,9] with thermal cycling at lower temperatures and hence less over–ageing effects from adjacent scans. This would increase the solute supersaturation, thereby increasing the hardness and decreasing the electrical conductivity both before and after ageing (while still maintaining a high relative density). In order to verify the correlation between electrical conductivity and densification further, five samples with E varying from 35 to 103 J/mm3 were selected for ageing at 500 °C until the conductivity values reached a plateau at >1.5 h, indicating that an equilibrium of solutes in solution was reached. The electrical conductivity was measured several times over the plateau regime for each sam-
ple, with averages plotted in Fig. 3h as a function of densification. The strong linear correlation provides a simple relationship between electrical conductivity and densification in the absence of solute effects. A comparison with the linear fitting results of the same samples in the as–fabricated condition reveals a similar slope. This confirms that changes in the as–fabricated electrical conductivity for E < 103 J/mm3 are dominated by porosity effects rather than by solute effects. 4. Conclusions This work shows that the combined effects of reduced densification due to incomplete melting at low energy densities and decreasing solute super saturation at high energy densities need to be considered if higher densification and better properties are to be achieved. For specimens with a low densification at E < 80 J/mm3, the reduced hardness and electrical conductivity are clearly dominated by porosity effects. When D > 99%, the effects of solute in solid solution become predominant. A good balance between porosity and solute supersaturation is obtained between E = 77 J/mm3 and E = 103 J/mm3. Finally, this work also provides a useful relationship between electrical conductivity and densification, which could be used as a fast and convenient way of evaluating the degree of densification after SLM. Acknowledgements This work was supported by the Australian Research Council (Grant No. IH130100008). The authors acknowledge use of the
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facilities at the Monash Centre for Additive Manufacturing and the Monash Centre for Electron Microscopy. Stephanie Giet and Arthur Li are thanked for their early help, while Kate Nairn and Peter Nichols are thanked for NMR assistance. References [1] [2] [3] [4]
L. Hao, S. Dadbakhsh, et al., J. Mater. Process. Technol. 209 (2009) 5793–5801. L.C. Zhang, D. Klemm, et al., Scripta Mater. 65 (2011) 21–24. W. Li, J. Liu, et al., Scripta Mater. 118 (2016) 13–18. S.T. Williams, P.J. Withers, et al., Scripta Mater. 122 (2016) 72–76.
[5] K.N. Amato, S.M. Gaytan, et al., Acta Mater. 60 (2012) 2229–2239. [6] F. Palm, P. Vermeer, et al., in: Proc. of 11th Intern. Conf. on Aluminium Alloys (ICAA11), DGM and Wiley VCH: Aachen, Germany, 2008. [7] K. Schmidtke, F. Palm, et al., Phys. Procedia 12 (2011) 369–374. [8] F. Palm, K. Schmidtke, in: Proc. of 9th Intern. Conf. on Trends in Welding Research, ASM International: Chicago, IL, 2012. [9] P.A. Rometsch, H. Zhong, et al., Scripta Mater. 87 (2014) 13–16. [10] T. Kimura, T. Nakamoto, Mater. Des. 89 (2016) 1294–1301. [11] X.J. Wang, L.C. Zhang, et al., Mater. Sci. Eng., A 597 (2014) 370–375. [12] Standard Test Methods for Metal Powders and Powder Metallurgy Products, Metal Powder Industries Federation, Princeton, USA, 2009. [13] F. Kutner, G. Lang, Aluminium 52 (1976) 322–326.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Characterisation of a novel Sc and Zr modified Al–Mg alloy fabricated by selective laser melting Yunjia Shi a,b, Paul Rometsch a,c,⇑, Kun Yang a,c, Frank Palm d, Xinhua Wu a,c a
Department of Materials Science and Engineering, Monash University, Clayton, VIC 3800, Australia School of Materials Science and Engineering, Central South University, Changsha 410083, China c Monash Centre for Additive Manufacturing, 11 Normanby Road, Notting Hill, VIC 3168, Australia d Airbus Group Innovations, IC1 Ottobrunn, 81663 Munich, Germany b
a r t i c l e
i n f o
Article history: Received 23 December 2016 Accepted 17 March 2017 Available online 18 March 2017 Keywords: Selective laser melting Metals and alloys Scandium Electrical conductivity Microstructure Nuclear magnetic resonance
a b s t r a c t Correlations between densification, hardness and electrical conductivity were investigated over a wide range of applied volumetric energy densities (E) for an Al–Mg–Sc–Zr alloy fabricated by selective laser melting. It is shown that porosity dominates electrical conductivity in the low E region up to 77 J/ mm3, while the contribution of solute in solution is more significant in the medium–high E region. Reasons for these differences are discussed and a linear relationship between electrical conductivity and densification in the absence of solute effects is presented. Ó 2017 Elsevier B.V. All rights reserved.
1. Introduction Selective laser melting (SLM) is a rapidly growing additive manufacturing (AM) technology, which has been used for fabricating steel [1], Ti [2–4], Al and Ni alloys [5]. Recently, Sc as an alloying element was introduced to aluminum alloys made by AM [6–8]. Compared with conventional casting alloys, additions of Sc and Zr present strikingly different effects on AM fabricated alloys both in terms of refined microstructures and improved mechanical properties [8]. The extremely rapid solidification rate during SLM allows much more Sc to be placed in solution than predicted by the relevant phase diagram. Normally, any subsequent solution heat treatment and quenching is not able to increase the amount of Sc in solution any further and may even decrease it [8,9]. The highly supersaturated solid solution obtained during SLM solidification provides excellent conditions for the precipitation of Al3(Sc,Zr) particles during ageing. The precipitation strengthening effect caused by these nano–scale coherent L12 phases improves the strength while maintaining good toughness and ductility [7]. The excellent performance of Al–Mg–Sc–Zr alloys in SLM makes them worthy of further investigation. The aim of this work is therefore to provide fundamental insights into the interrelationships ⇑ Corresponding author at: Department of Materials Science and Engineering, Monash University, Clayton, VIC 3800, Australia. E-mail address: [email protected] (P. Rometsch). http://dx.doi.org/10.1016/j.matlet.2017.03.089 0167-577X/Ó 2017 Elsevier B.V. All rights reserved.
between laser scanning parameters and solute in solution, precipitation, porosity, hardness, electrical conductivity and microstructure.
2. Experimental The chemical composition of the powder is Al–3.40Mg–1.08Sc– 0.50Mn–0.44Cu–0.23Zr–0.14Si–0.08Fe (wt%). Samples were fabricated on an EOSINT M280 powder bed machine with a laser beam diameter of 100 lm; a hatch distance (h) of 100 lm and a layer thickness (t) of 30 lm. A series of 18 mm 18 mm 10 mm rectangular specimens were fabricated onto an Al substrate using a platform temperature of 35 °C and a bi–directional scan strategy. The laser scanning speed (v) ranged from 800 to 3000 mm/s, and the laser power (P) ranged from 220 to 370 W. In order to evaluate the effect of energy input on the powder deposition process, the applied volumetric energy density (E) was defined by E ¼ P=vht [10,11]. The densification (D) was averaged from three measurements using the Archimedes method [11,12]. The electrical conductivity (EC) of the cross–section was measured using a Foerster SIGMATESTÒD 2.068 eddy current device at room temperature. The Vickers hardness was measured on the same section using a Duramin A300 hardness tester with a 1 kg load. Ageing was performed in a Carbolite air circulation furnace at 300 °C and 500 °C, followed
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by water quenching. Backscattered electron micrographs (BSE) and energy–dispersive X–ray spectroscopy (EDX) were obtained using a JEOL 7001 FEG scanning electron microscope. Additionally, nuclear magnetic resonance (NMR) spectroscopy was used to evaluate the fractions of Sc in solid solution and precipitates on a Bruker300 MHz Ultra Shield solid–state NMR spectrometer. Peak analysis using Dmfit software and NMR methods are described elsewhere [9,10]. 3. Results and discussion Fig. 1a shows the variation in densification and electrical conductivity with energy density for as–fabricated specimens. The increase of electrical conductivity with increasing E correlates extremely well with the densification trend at E < 80 J/mm3. However, the densification reaches a maximum of 99.98% at E = 103 J/ mm3 and then decreases slightly at E = 154 J/mm3, the electrical conductivity increases almost linearly with E from 80 to 154 J/ mm3. Fig. 1b shows a strong linear relationship between EC and densification for specimens with D < 99.5%, suggesting that the porosity level determines the electrical conductivity in this densification range. For almost fully dense materials with D > 99.5%, the EC appears to be dominated by the amount of solute in solution [9,13], with the solute supersaturation decreasing as E increases. In order to test these hypotheses, five samples were selected based on a constant P = 370 W and v varying from 800 to 3000 mm/s (Fig. 2). The electrical conductivity increases monotonically with increasing E (decreasing laser scanning speed) in both the as–fabricated and aged conditions, but the as–fabricated hardness first increases from E = 41 J/mm3 to E = 77 J/mm3, and then decreases again towards E = 154 J/mm3. When E < 77 J/mm3, both
the EC and hardness increase with increasing densification. It should be noted that the hardness error bars (Fig. 2b and c) are larger at D < 99% (higher laser scanning speed) as a result of the irregularly shaped pores formed due to incomplete melting of the powder. Although the density slightly increases when E increases to 103 and 154 J/mm3, the hardness decreases. This decrease in hardness and increase in EC with increasing E from 77 to 154 J/ mm3 suggests that much more heat is placed into melt pools at lower laser scanning speeds, leading to the partitioning of solutes to more coarse non–hardening precipitates, either due to a decreasing solidification rate and/or an increasing over–ageing effect from the thermal cycling. After peak ageing at 300 °C for 12 h (Fig. 2c), the increase in hardness by >50 HV1 means that a significant amount of nano–scale Al3Sc and/or Al3(Sc,Zr) must have precipitated. The concomitant increase in conductivity by 5%IACS is primarily due to the loss of solute from solution. The BSE images in Fig. 3 reveal colonies of both small columnar grains and sub–micron equiaxed grains. For low E, EDX results show some small Si–enriched particles (Point A) and larger/ brighter Cu–enriched particles along the grain boundaries (point B). These particles occur in higher number densities in the equiaxed grain regions. A few diamond–shaped particles (points C and D) are observed for samples with higher energy densities, especially at 154 J/mm3. EDX results show that these particles are rich in both Sc and Zr (point C contains 2.37 wt% Sc and 1.44 wt% Zr, while point D contains 3.31 wt% Sc and 2.22 wt% Zr). Both the morphology and composition of these particles are characteristic of primary Al3(Sc,Zr) particles. With increasing E, both the volume fraction and size of these particles increase. Furthermore, the bright white non–hardening particles generally become coarser and exhibit a more over–aged appearance with increasing energy density (Fig. 3).
Fig. 1. (a) Plots of densification and EC against energy density for as–fabricated specimens, and (b) linear relationship between EC and densification for specimens with D < 99.5%.
Fig. 2. Effects of energy density and corresponding laser scanning speeds at 370 W on (a) densification and porosity by optical microscopy, (b) as–fabricated hardness and EC, and (c) peak aged hardness and EC.
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Fig. 3. BSE images at E of: (a, b) 51 J/mm3 (2400 mm/s), (c, d) 77 J/mm3 (1600 mm/s), and (e, f) 154 J/mm3 (800 mm/s); (g) NMR spectra for as–fabricated samples with calculated mass fractions of Sc atoms surrounded by Al atoms in solid solution marked beside the peaks; (h) linear fitting correlations of EC vs. densification both after equilibration at 500 °C for up to 72 h and in the as–fabricated condition.
This explanation can be verified by the NMR spectra shown in Fig. 3g, where the peak at 1700 ppm represents Sc atoms dissolved in the Al lattice and surrounded by Al atoms only, while the peak at 1050 ppm represents Sc in Al3Sc precipitates. The fraction of Sc in solution was calculated as the ratio of the area under the Gaussian peak at 1700 ppm relative to the area under the whole spectrum. With increasing E, the fraction of Sc in solid solution gradually decreases. Together with the SEM results, this confirms that the higher conductivity and lower hardness at E = 154 J/mm3 is due to a reduced as–fabricated solute supersaturation from the higher heat input, i.e. more Sc and other solute species have precipitated as coarse particles during SLM (white particles in Fig. 3). Generally, a slow scanning speed of 800 mm/s provides more heat input and more time to form primary and/or over–aged coarse non–hardening precipitates that may occur in this system, e.g. Al3Sc, Al3Zr, Al3(Sc,Zr), Al2CuMg, Mg2Si, Mn–dispersoids or Fe–intermetallics. By contrast, the higher scanning speed of 1600 mm/s leads to a faster solidification cooling rate well in excess of 1000 K/s [8,9] with thermal cycling at lower temperatures and hence less over–ageing effects from adjacent scans. This would increase the solute supersaturation, thereby increasing the hardness and decreasing the electrical conductivity both before and after ageing (while still maintaining a high relative density). In order to verify the correlation between electrical conductivity and densification further, five samples with E varying from 35 to 103 J/mm3 were selected for ageing at 500 °C until the conductivity values reached a plateau at >1.5 h, indicating that an equilibrium of solutes in solution was reached. The electrical conductivity was measured several times over the plateau regime for each sam-
ple, with averages plotted in Fig. 3h as a function of densification. The strong linear correlation provides a simple relationship between electrical conductivity and densification in the absence of solute effects. A comparison with the linear fitting results of the same samples in the as–fabricated condition reveals a similar slope. This confirms that changes in the as–fabricated electrical conductivity for E < 103 J/mm3 are dominated by porosity effects rather than by solute effects. 4. Conclusions This work shows that the combined effects of reduced densification due to incomplete melting at low energy densities and decreasing solute super saturation at high energy densities need to be considered if higher densification and better properties are to be achieved. For specimens with a low densification at E < 80 J/mm3, the reduced hardness and electrical conductivity are clearly dominated by porosity effects. When D > 99%, the effects of solute in solid solution become predominant. A good balance between porosity and solute supersaturation is obtained between E = 77 J/mm3 and E = 103 J/mm3. Finally, this work also provides a useful relationship between electrical conductivity and densification, which could be used as a fast and convenient way of evaluating the degree of densification after SLM. Acknowledgements This work was supported by the Australian Research Council (Grant No. IH130100008). The authors acknowledge use of the
350
Y. Shi et al. / Materials Letters 196 (2017) 347–350
facilities at the Monash Centre for Additive Manufacturing and the Monash Centre for Electron Microscopy. Stephanie Giet and Arthur Li are thanked for their early help, while Kate Nairn and Peter Nichols are thanked for NMR assistance. References [1] [2] [3] [4]
L. Hao, S. Dadbakhsh, et al., J. Mater. Process. Technol. 209 (2009) 5793–5801. L.C. Zhang, D. Klemm, et al., Scripta Mater. 65 (2011) 21–24. W. Li, J. Liu, et al., Scripta Mater. 118 (2016) 13–18. S.T. Williams, P.J. Withers, et al., Scripta Mater. 122 (2016) 72–76.
[5] K.N. Amato, S.M. Gaytan, et al., Acta Mater. 60 (2012) 2229–2239. [6] F. Palm, P. Vermeer, et al., in: Proc. of 11th Intern. Conf. on Aluminium Alloys (ICAA11), DGM and Wiley VCH: Aachen, Germany, 2008. [7] K. Schmidtke, F. Palm, et al., Phys. Procedia 12 (2011) 369–374. [8] F. Palm, K. Schmidtke, in: Proc. of 9th Intern. Conf. on Trends in Welding Research, ASM International: Chicago, IL, 2012. [9] P.A. Rometsch, H. Zhong, et al., Scripta Mater. 87 (2014) 13–16. [10] T. Kimura, T. Nakamoto, Mater. Des. 89 (2016) 1294–1301. [11] X.J. Wang, L.C. Zhang, et al., Mater. Sci. Eng., A 597 (2014) 370–375. [12] Standard Test Methods for Metal Powders and Powder Metallurgy Products, Metal Powder Industries Federation, Princeton, USA, 2009. [13] F. Kutner, G. Lang, Aluminium 52 (1976) 322–326.