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Optimizing Laser Conditions and Controlling Microstructure/Properties of Laser Powder Bed Fused Al-Si Alloys 査読有り Open Access

Suzuki A., Takata N., Kobashi M., Kato M.

Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy 69 巻 ( 10 ) 頁： 417 - 425 2022年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Funtai Oyobi Fummatsu Yakin/Journal of the Japan Society of Powder and Powder Metallurgy

In the laser beam powder bed fusion (PBF-LB) processes, laser parameters need to be customized for fabricating dense components. Al-Si alloys are representative Al alloys used for the PBF-LB processes. The Al-Si alloys fabricated by the PBF-LB processes exhibit characteristic microstructures and mechanical properties, which are affected by the laser parameters. This paper describes the effect of laser conditions on the relative density, microstructure, and mechanical properties of Al-12Si (mass%) alloy fabricated by the PBF-LB process. The first topic is a machine-learning-assisted exploration of laser parameters (laser power and scan speed) for fabricating dense Al-12Si alloy parts. Using a neural network model, the laser condition range for fabricating dense Al-12Si alloy parts is predicted. A methodology for accurately predicting the laser condition range for fabricating dense components is introduced. The second topic is controlling the microstructures and mechanical properties of the dense Al-12Si alloys. Variations in α-Al crystal grain size/orientation, the width of primary α-Al phase, and solute Si content in α-Al matrix with laser conditions are introduced. The changes in mechanical properties with laser conditions and correlation with microstructural features are also described.

DOI： 10.2497/jjspm.69.417

Open Access

Scopus

Influence of added fourth elements on creep properties of heat-resistant Al-Mg-Zn ternary alloys at 200°C 査読有り Open Access

Kondo M., Suzuki T., Li R., Takata N.

Keikinzoku/Journal of Japan Institute of Light Metals 72 巻 ( 6 ) 頁： 473 - 481 2022年

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Keikinzoku/Journal of Japan Institute of Light Metals

The effect of Cu or Ni addition on creep properties of a heat-resistant aluminum (Al) alloy (with a composition of Al-5Mg-3.5Zn (mol%)) strengthened by precipitates of T-Al6Mg11Zn11 intermetallic phase was investigated. The quaternary alloys with various Cu contents (0.25-3 mol%) or Ni contents (0.5-2 mol%) were solution-treated at 470 °C and then aged at 200°C for 10 hours. The creep tests were conducted using the heat-treated specimens at 200°C under 105 MPa. Both Cu and Ni additions increased the creep rupture time. The 1 mol% Cu added alloy exhibited the longest creep rupture time due to the enhanced precipitation of the refined intragranular phases (T or MgZn2 phases). However, more than 2 mol% Cu addition led to the transition of T phase to S-Al2CuMg phase formed on grain boundaries. The phase transition might have a detrimental effect on creep rupture time. In the Ni-added alloy specimen, the creep rupture time became longest when 1 mol% Ni was added. The added Ni element promoted the formation of the Al3Ni phase on the grain boundaries, resulting in the suppression of connecting cavities formed on grain boundaries in creep deformation.

DOI： 10.2464/JILM.72.473

Open Access

Scopus

Enhancement in strength and ductility of laser powder bed fused Al–12Si alloy by introducing nanoscale precipitates 査読有り国際誌

Liu M., Takata N., Suzuki A., Kobashi M., Kato M.

Additive Manufacturing Letters 1 巻頁： 100008 2021年12月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Additive Manufacturing Letters

In order to manage both the strength and ductility of Al–Si alloys additively manufactured by laser powder bed fusion (L-PBF), an attempt was made to introduce nanoscale precipitates within the α-Al (fcc) supersaturated solid solution using the L-PBF manufactured Al–12%Si alloy by artificial aging treatments. The aging treatment at 120°C improved both the tensile strength and ductility (total elongation) of the L-PBF manufactured specimen. The simultaneous strength–ductility enhancement is due to the homogeneously distributed nanoscale Si precipitates that enhanced the strain hardening. These results provide new insights for overcoming the strength-ductility trade-off in the L-PBF manufactured Al alloys.

DOI： 10.1016/j.addlet.2021.100008

Scopus

Precipitation morphology and kinetics of T-Al6Mg11Zn11 intermetallic phase in Al–Mg–Zn ternary alloys 査読有り国際誌

Takata N., Takagi R., Li R., Ishii H., Suzuki A., Kobashi M.

Intermetallics 139 巻 2021年12月

担当区分：筆頭著者,　責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Intermetallics

This study was undertaken to understand the fundamentals of T-Al6Mg11Zn11 intermetallic phase precipitation in heat-resistant Al–Mg–Zn ternary alloys, with the goal of further strength improvements. The thermodynamic assessment involved three alloy compositions, Al–4Mg–4.5Zn, Al–5Mg–3.5Zn, and Al–7Mg–1.5Zn (at%), with the T phase in a fixed fraction (approximately 6–7.5%) in equilibrium with the α-Al phase at 300 °C. The alloy compositions were set on different tie-lines between the α-Al and T phases in the two-phase region, resulting in varied compositions of each phase. In the three experimental alloys aged at 300 °C, the T phase precipitated on the grain boundaries of the α-Al matrix, and granular precipitates were homogeneously dispersed intragranularly. There was no significant difference in the precipitation morphology. It was demonstrated that the lattice parameters of the T and α-Al phases could be controlled based on the alloy composition and applied heat treatments. However, the lattice parameters have no significant effect on the precipitation morphologies of the thermodynamically stable T phase in the Al–Mg–Zn ternary alloys. The Zn-rich Al–4Mg–4.5Zn alloy exhibited a pronounced softening behavior after 10 h of aging due to the enhanced coarsening of precipitates in the α-Al matrix. The thermal instability of the precipitates was responsible for the transformation sequence from the initially formed metastable phases (η-Zn2Mg associated phases) to the stable T phase. These results provided a fundamental insight that alloy strengthening by introducing thermodynamically stable intermetallic phases is essential for sustaining the strength of heat-resistant Al–Mg–Zn ternary alloys after long-term treatment at elevated temperatures.

DOI： 10.1016/j.intermet.2021.107364

Scopus

Control of microstructural characteristics and mechanical properties of AlSi12 alloy by processing conditions of laser powder bed fusion 査読有り国際誌

Suzuki A., Miyasaka T., Takata N., Kobashi M., Kato M.

Additive Manufacturing 48 巻 2021年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Additive Manufacturing

To elucidate the possibility of controlling the microstructure and mechanical properties of Al–Si alloys additive-manufactured by laser powder bed fusion (L–PBF), the relationship among the laser conditions, microstructural characteristics (crystal grain, cellular microstructure, and solute Si in α-Al matrix), and tensile properties of L–PBF manufactured AlSi12 alloy samples was investigated. The crystal grain size and fraction of <001> oriented α-Al crystal grains toward the building direction increased as the laser power became higher and scanning velocity became slower. The width of cellular microstructure (sub–cell size) where the primary α-Al phase was surrounded by α-Al/Si eutectic microstructure increased as the laser power became higher and scanning velocity became slower. The refinement of microstructure was attributed to the solidification under high cooling rate, which was achieved by low laser power and high scanning velocity. The area fraction of Si phase analyzed from FE–SEM images tended to decrease as the laser power became higher and scanning velocity became slower, suggesting the possibility of solute Si concentration in α-Al matrix controlled by laser conditions. The STEM/EDS analysis revealed high concentration of solute Si in the α-Al matrix (above a solubility limit of 1.5 mol% in the Al–Si binary system) of L–PBF manufactured AlSi12 alloy samples and its concentration became higher in the sample manufactured using a higher laser power. The tensile tests of as–built AlSi12 specimens fabricated under various laser conditions were also performed. High strength and high ductility tended to be achieved when high power laser was applied in slow laser scanning velocity. The 0.2% proof stress was relatively higher when the laser scanning velocity was faster. The mechanical properties correlated with crystal grain size and sub–cell size rather than solute Si in the α-Al matrix. These results provide new insights to control mechanical performance of AlSi12 alloy via L–PBF processing parameters.

DOI： 10.1016/j.addma.2021.102383

Scopus

Precipitation Hardening at Elevated Temperatures above 400 degrees C and Subsequent Natural Age Hardening of Commercial Al-Si-Cu Alloy 査読有り国際誌

Li Ruoqi, Takata Naoki, Suzuki Asuka, Kobashi Makoto, Okada Yuji, Furukawa Yuichi

MATERIALS 14 巻 ( 23 ) 2021年12月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials

The precipitation of intermetallic phases and the associated hardening by artificial aging treatments at elevated temperatures above 400◦ C were systematically investigated in the commer-cially available AC2B alloy with a nominal composition of Al–6Si–3Cu (mass%). The natural age hardening of the artificially aged samples at various temperatures was also examined. A slight increase in hardness (approximately 5 HV) of the AC2B alloy was observed at an elevated temperature of 480◦ C. The hardness change is attributed to the precipitation of metastable phases associated with the α-Al15 (Fe, Mn)3 Si2 phase containing a large amount of impurity elements (Fe and Mn). At a lower temperature of 400◦ C, a slight artificial-age hardening appeared. Subsequently, the hardness decreased moderately. This phenomenon was attributed to the precipitation of stable θ-Al2 Cu and Q-Al4 Cu2 Mg8 Si6 phases and their coarsening after a long duration. The precipitation sequence was rationalized by thermodynamic calculations for the Al–Si–Cu–Fe–Mn–Mg system. The natural age-hardening behavior significantly varied depending on the prior artificial aging temperatures ranging from 400◦ C to 500◦ C. The natural age-hardening was found to strongly depend on the solute contents of Cu and Si in the Al matrix. This study provides fundamental insights into controlling the strength level of commercial Al–Si–Cu cast alloys with impurity elements using the cooling process after solution treatment at elevated temperatures above 400◦ C.

DOI： 10.3390/ma14237155

Web of Science

Scopus

Controlling WC/Co two-phase microstructure of cemented carbides additive-manufactured by laser powder bed fusion: Effect of powder composition and post heat-treatment 査読有り国際誌

Ibe H., Kato Y., Yamada J., Kato M., Suzuki A., Takata N., Kobashi M.

Materials and Design 210 巻 2021年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Elsevier Ltd.

In this study, an attempt is made to control the WC-Co two-phase microstructures by laser powder-bed fusion (LPBF) process using cemented carbide powders with different compositions of WC-25Co (mass%) and WC-17Co (mass%) and post heat-treatment at 1380 °C. The as-built cemented carbide samples had different microstructures from those of the cemented carbides fabricated by conventional manufacturing methods. The microstructures of the as-fabricated WC-25Co and WC-17Co cemented carbides were characterized by two types of regions. Region 1 consisted of W2C and W3Co3C phases, including numerous pores and defects. Region 2 consisted of WC and Co phases. Post heat-treatment of the LPBF-built WC-25Co sample at 1380 °C led to the formation of a defect-free WC-Co two-phase microstructure. In contrast, the W3Co3C phase remained in the LPBF-built WC-17Co sample even after heat treatment. The addition of carbon to the WC-17Co powder prevented the formation of the W3Co3C phase in the cemented carbide processed by LPBF and subsequent heat treatments. The addition of carbon to the WC-17Co powder had a slight effect on the hardness of as-fabricated samples, but reduced the hardness of heat-treated samples. The reduced hardness was attributed to the increased volume fractions of the WC and W3Co3C phases.

DOI： 10.1016/j.matdes.2021.110034

Scopus

その他リンク： https://www.sciencedirect.com/science/article/pii/S026412752100589X

Effect of added stabilizing elements on thermal activation process of plastic deformation in 18Cr ferritic stainless steel 査読有り国際誌

Li H., Takata N., Kobashi M., Yoshino M.

Materials Science and Engineering A 824 巻 2021年9月

担当区分：責任著者記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Materials Science and Engineering A

The effects of a trace amount (~0.1 at.%) of added stabilizing elements (Nb, Ti, and Zr) on the tensile properties of 18Cr ferritic stainless steel sheets at strain rates ranging from 10−3–102 s−1 (from ordinary quasi-static deformation to dynamic deformation) were investigated. The additional Ti or Zr elements formed coarse carbide or nitride precipitates, which consumed interstitial solute elements (C and/or N) in the ferrite matrix. In the Nb-added steel, however, only fine NbN precipitates with a few hundred nanometers in size were observed locally, implying a small amount of solute Nb in the ferrite matrix. Ti or Zr additions had only a slight effect on the deformation resistance of 18Cr ferritic steel sheets and strain rate sensitivity (m) of the flow stress, however, the Nb addition increased the deformation resistance and significantly reduced the strain rate sensitivity. The measured activation volume (v*) values of the Ti- and Zr-added steels (62 b3 and 66 b3) were almost equivalent to one of the 18Cr base steel (64 b3). This result suggested that a general thermally activated process for screw dislocation motion is controlled by double-kink nucleation, which is slightly affected by Ti or Zr additions. The high v* value (106 b3) of the Nb-added steel indicated that the thermally activated process of plastic deformation would be associated with the substitutional solute Nb atoms (act as short-range obstacles) interacting with the moving dislocations. These results showed that the Nb element played a distinct role in plastic deformation from the other stabilizing elements of Ti and Zr.

DOI： 10.1016/j.msea.2021.141866

Scopus

Dual plateau stress of C15-type topologically close-packed lattice structures additive-manufactured by laser powder bed fusion 査読有り国際誌

Liu X., Suzuki A., Takata N., Kobashi M., Kato M.

Scripta Materialia 202 巻 2021年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Scripta Materialia

Imitating crystal structures offers new avenues to design lattice structures composed of unit cells with nodes (act as atoms) and struts (act as atomic bonds). We found out unique dual plateau regions in the stress–strain curves of lattice structures inspired by topologically close-packed (TCP) structure of C15 Laves phase (AB2-type intermetallic compounds) and manufactured via the laser powder bed fusion. X-ray computed tomography of compressively deformed lattice structures as well as finite element analysis revealed that the existence of two kinds of units with different relative density caused the dual plateau regions. In addition, the C15 lattice structures exhibited a hybrid deformation mode of bending- and stretch-dominated deformations and can absorb high total energy of 5.0 MJ·m−3 in two stress levels.

DOI： 10.1016/j.scriptamat.2021.114003

Scopus

Control of surface micro− structure for Al alloy/polymer joining fabricated by laser process using Al− Ti− C powders: Effect of powder composition 査読有り国際誌

Seung−Gwang Kim, Asuka Suzuki, Naoki Takata, Makoto Kobashi

Journal of Advanced Joining Processes 4 巻頁： 100068 2021年7月