2023 Volume 64 Issue 12 Pages 2838-2844
The six best papers were awarded by The Japan Institute of Light Metals (JILM) and The Japan Society for Technology of Plasticity (JSTP) in Materials Transactions. Here, the awarded papers are briefly summarized as current trends in research of Materials Transactions. Among the six best papers, three were from JILM and the two of the three were selected for young scientists whose ages are 30 or below. All the six best papers were originally published in Japanese in Journal of the Japan Institute of Light Metals and Journal of the Japan Society for Technology of Plasticity as cutting-edge research in JILM and JSTP which are major companions of Materials Transactions.
We are pleased to introduce the best papers awarded by The Japan Institute of Light Metals (JILM) and The Japan Society for Technology of Plasticity (JSTP).1–6) Materials Transactions publishes papers from 14 institutes and societies where JILM and JSTP are two active companions [https://jimm.jp/en/publications/journal.html]. Authors may submit papers through either one of the 14 institutes and societies depending on the specialties in terms of materials, analytical procedures and processing technologies, although some institutes and societies accept the submission only from members including expected members. Thus far, Materials Transactions has announced high quality papers which received the best papers awards in 2019, 2020 and 2021 from The Japan Institute of Metals and Materials (JIMM),7–9) of which editorial office coordinates the publication from the 14 institutes and societies.
In this article as a current trend in research, the six best papers were introduced,1–6) which were selected from cutting edge research in JILM and JSTP: three best papers are from each of JILM and JSTP and two out of the three in JILM2,3) are for young scientists in JILM.
The selection of the three best papers in JILM1–3) was made in two-step processes: first through a recommendation committee and second through an evaluation committee. The members in the recommendation committee nominates around 10 papers out of all the papers published through JILM in the past one year. Members of the evaluation committee then score the whole nominated papers, and the three papers earned the highest scores are awarded as Light Metal Paper Prize. If the first author is at the age of 30 or less, the corresponding paper may win the award as Light Metal Paper-by-Newcomer Prize. The selection of the best paper in JILM is made based on the following criterions: (a) sufficient originality, (b) highly influential (good potential for significant research advancement), (c) solving long-term problem, (d) being far ahead of others and (e) enormous contribution to application development. These evaluation criteria are the same for JIMM except the last one.
For the three best papers awarded by JSTP,4–6) nomination was first made by recommendation and application from the papers published through JSTP in the past two years. Such papers are then evaluated by several members of the selection committee for the best papers.
Here, the six awarded papers1–6) are introduced below with brief summaries provided by the corresponding authors.
Many experimental studies on diffusion in titanium-based binary alloys containing α- or β-stabilizing elements have been performed.10–15) Other than investigation of the diffusion of titanium-based ternary alloys in a Ti–V–Zr system by Brunsch et al.,16) a Ti–Al–Cr system,17) a Ti–Al–V system,18) a Ti–Al–Co system19) and a Ti–Al–Fe system,20) the number of studies on the ternary diffusion is limited. Therefore, the accumulation of the data from diffusion studies is desired for multi-component titanium alloys.
As a series of diffusion studies of multi-component titanium alloys, the purposes of the present work are as follows: (a) to determine, using the Matano-Kirkaldy method,21–23) the binary and ternary interdiffusion coefficients in the β solid solutions of the ternary Ti–Al–Zr alloys at 1473 K and the impurity diffusion coefficients of Zr in Ti–Al alloys at 1473 K, and (b) to estimate the thermodynamic interactions24) between solute and solute atoms (and solvent-solute atoms) in β Ti–Al–Zr solid solutions at 1473 K.
Interdiffusion in Ti-rich β solid solutions in Ti–Al–Zr alloys was investigated at 1473 K. In the β Ti–Al–Zr alloys, the main interdiffusion coefficients (i.e., $\tilde{D}_{\text{AlAl}}^{\text{Ti}}$ and $\tilde{D}_{\text{ZrZr}}^{\text{Ti}}$, respectively) and the cross interdiffusion coefficients, (i.e., $\tilde{D}_{\text{AlZr}}^{\text{Ti}}$ and $\tilde{D}_{\text{ZrAl}}^{\text{Ti}}$, respectively) have positive values, as well as a slight concentration dependence. The values of $\tilde{D}_{\text{ZrZr}}^{\text{Ti}}$ are larger than those of $\tilde{D}_{\text{AlAl}}^{\text{Ti}}$. As shown in Fig. 1, in Ti–Al–X (= V, Cr, Fe, Co, Zr) alloys, the values of the main coefficients are $\tilde{D}_{\text{VV}}^{\text{Ti}} < \tilde{D}_{\text{CrCr}}^{\text{Ti}} < \tilde{D}_{\text{ZrZr}}^{\text{Ti}} < \tilde{D}_{\text{FeFe}}^{\text{Ti}} < \tilde{D}_{\text{CoCo}}^{\text{Ti}}$ at 1473 K.
Comparison of (a) main interdiffusion coefficients and (b) main interdiffusion coefficients in Ti–Al–X (X = V, Cr, Fe, Co, Zr) alloys at 1473 K.1)
Repulsive interactions occur between Al and X (= V, Cr, Fe, Co, Zr) atoms in the Ti–Al–X alloys, because the ratio values of the cross coefficients to the main ones are positive in sign. On the other hand, the interactions between Ti (solvent) and X (= V, Cr, Fe, Co, Zr) (or Al) atoms are attractive in the present alloys because the ratio of the converted interdiffusion coefficients is negative values.
Al–Mg–Si alloys are known to exhibit a negative effect of two-step aging, that is, when they are kept at room temperature after solution treatment, age hardening is difficult to obtain in subsequent aging.25–27) It is considered that this is because the nanoclusters formed by holding at room temperature inhibit the precipitation of the β′′ phase, which contributes to age hardening. Though, it is not sufficiently clear what kind of clusters are formed. This is thought to be due to the formation of nanoclusters at room temperature, which inhibit the formation of the β′′ phase that contributes to age hardening. In this study, the formation of clusters in Al–1.04 mass%Si–0.55 mass%Mg alloys at the early stages of natural aging was investigated by soft X-ray XAFS measurements and first principles calculation.28–30) XAFS measurements near the Mg–K and Si–K edges were carried out at the BL27SU beamline at SPring-8. It was found that the absorption edge energies changed with aging as shown in Fig. 2. Density functional theory (DFT) calculations were used to determine the valence electron densities near Si and Mg atoms and to simulate the Si–K and Mg–K edge spectra for some cluster models. Based on the results, it was demonstrated that Si and Mg atoms formed clusters in four stages (I–IV) during natural aging. In stage I, Si-vacancy pairs were rapidly formed, and the formation of Mg-vacancy pairs and Mg–Si-vacancy clusters also proceeded. In stage II, vacancies were released from the clusters formed in stage I. In stage III, the clusters coalesced with Mg-vacancy pairs and the Si/Mg ratio within the clusters decreased. In stage IV, the cluster coarsened through the release of vacancies.
XANES spectra near Si–K edge of Al–Mg–Si alloys and reference samples.2)
This paper reported the effects of Cu or Ni additions on the precipitation of intermetallic phases in the heat-resistant aluminum alloy with a ternary composition of Al–5Mg–3.5Zn (mol%) strengthened by fine precipitates of T–Al6Mg11Zn11 intermetallic phase.31,32) The fourth element of Cu and Ni at 1 mol% was added to the Al–Mg–Zn ternary alloy as the modified quaternary alloy. The quaternary alloys were solution-treated at 480°C and subsequently aged at 300°C for different periods. Both Cu and Ni additions have a slight effect on the age-hardening of these alloys at 300°C. The added Cu element partitioned into not only the T–Al6Mg11Zn11 phase but also the η-Zn2Mg phase precipitated in the α-Al matrix. The observed Cu enrichment in the precipitates of the T phase for strengthening of heat-resistant Al alloys indicated high stability of the T phase in the Al–Mg–Zn–Cu quaternary system. The experimental result was different from the thermodynamic calculations using the existing database, whereas such a result was found in conventional Al–Mg–Zn–Cu alloys.33,34) The added Ni element enhanced the formation of the fine Al3Ni phase located at grain boundaries (Fig. 3) and slightly influenced the precipitation of the T phase in the grain interior. These results provided new insights into designing novel heat-resistant Al alloys strengthened by different mechanisms in the Al–Mg–Zn–Cu–Ni quinary system.35,36)
(a) STEM-HAADF image and (b)–(e) corresponding EDS element maps for the Ni-added alloy (Al–5Mg–3.5Zn–1Ni quaternary alloy) aged at 300°C for 1 h.3)
In recent years, application of ultrahigh-strength steels (UHSS) to automobile parts has been advanced in order to reduce the weight of automobile bodies and improve collision safety.37–40) Most automobile frame parts are manufactured by press forming, which has the advantage of high productivity. However, one problem in press forming of UHSS is poor dimensional accuracy caused by springback.41,42) Because the stress at the bottom dead center of press forming increases as the material strength increases, the dimensional accuracy of UHSS deteriorates due to the increased amount of springback. In addition, UHSS have large material strength scattering in mass production. Therefore, the stress fluctuation at the bottom dead center of press forming is also large and dimensional scattering increases.
In this study, camber back, which occurs in longitudinally curved parts, was examined, and a new forming method whereby dimensional scattering of camber back can be suppressed by the Bauschinger effect43,44) was developed. The new method consists of two processes. In the 1st process, a blank is formed with a small radius of curvature compared with that in the 2nd-process. In the 2nd process, that part is formed to a larger radius of curvature than in the 1st process, and the Bauschinger effect is utilized to decrease the amount of camber back. The new method was applied to hat-shaped models of 590, 980, and 1180 MPa-grade steels in which the radius of curvature in the longitudinal direction was 1600 mm. The experimental results showed that the difference in the amount of camber back between the 590 MPa and 1180 MPa steels formed by the developed method decreased by 95% compared with parts formed by the conventional method (Fig. 4).
Effects of tensile strength of steel sheet on radius of curvature of web of panel formed in 2nd processes in experiment and FEM.4)
The strength of automotive body parts is getting higher for the weight reduction and collision safety improvement of automotive bodies,45) and the use of ultra-high strength sheet steels with a tensile strength of 1180 MPa or more is expanding worldwide.
An automotive part which has a multi-curved shape made of three straight portions connected by two curved portions, curved in the opposite directions each other, is one of the most difficult parts to press-form with ultra-high strength sheet steel because fractures and wrinkles are apt to generate at its curved portions.46)
Various countermeasures against the fracture in the outside of curved portions have been proposed such as the utilization of friction resistance and of deformation resistance of material.47–49) On the other hand, the addition of bulge shapes to absorb excess material have been known as a countermeasure against the wrinkles in the inside of curved portions.50)
The authors developed a new technique for suppressing fractures and wrinkles in the curved segment by causing in-plane shear deformation in the straight segment between the two curved segments.
As shown in Fig. 5, the developed process consists of two steps: (1) draw forming to induce in-plain shear strain, (2) bending to form the final multi-curved shape. In laboratory experiments, forming a simple multi-curved model shape, in-plane shear deformation which can suppress fractures and wrinkles was successfully brought about in the expected areas in the first draw forming. With the support of the in-plane shear deformation, the target model shape could be formed in the second bending without any fractures and wrinkles.
Developed press-forming technique using in-plane shear deformation.5)
Then, press trials of an automotive part, a front-side-member rear, were conducted with 1180 MPa grade ultra-high strength steel sheets, and the results demonstrated the effectiveness of the developed technique.
The homogenization method51,52) is effective for analyzing macroscopic mechanical properties from the substructure of a material. In perforated sheet metal, macroscopic mechanical properties depend on the pattern of hole arrangement.53–55) In this study, the macro–plastic properties of perforated sheets with 60° standard staggered and 90° square arrangements are modeled. Biaxial stress is applied to the unit cells given the periodic boundary condition, and the contours of equal plastic work56) are obtained. The yield surfaces of the perforated sheets on the tension–compression combined stress state are strongly affected by the hole arrangement. To model the yield surface, a yield function for the rotational symmetry peculiar to the perforated sheet is proposed. The yield surfaces are modeled using the CPB2006 yield function57) that takes into consideration tension–compression asymmetry. Also, a surface–interpolated differential hardening model58,59) is applied to model the changes of yield surfaces. Figure 6 shows the modeled yield surfaces with stress points of equal plastic work contours. The analysis results obtained using the modeled yield surfaces are compared with the experimental ones obtained on the uniaxial tensile and deep drawing tests. The results of both tests show good agreement.
Equal plastic work contours of unit cell analyses and yield loci modeled using differential hardening CPB2006 functions (plot: unit cell analysis, thick line: representative yield function, and dashed line: interpolated surface).6)
All the best papers introduced above were originally published in Japanese in Journal of the Japan Institute of Light Metals60–62) and Journal of the Japan Society for Technology of Plasticity.63–65) They were translated to English following the rule of Materials Transactions.
Adding further comments for JILM and JSTP, JILM was established in 1951 as an academic society for the science and technology for light metals such as Al, Mg, Ti and their alloys. Articles of 25–30 per year are published through JILM, which come to about 5% of the total in Materials Transactions. In 2022, a special issue entitled “Aluminium and its Alloys for Zero Carbon Society” was edited by JILM,66) collecting one overview paper,67) two review papers68,69) and 24 regular papers70–93) and published in the February issue, 2023. They were selected with strict review processes for the presentations made in The 18th International Conference on Aluminium Alloys (ICAA 18), Toyama, Japan on September 4–8, 2022.
For JSTP, the formal establishment was made in 1961, and now it covers a wide range of areas with a total of 19 committees such as Roll Forming, Rolling, Process Tribology, Tube Forming, Sheet Metal Forming, Forging, High Energy Rate Forming, Polymer Processing, Mashy-State/Semi-Solid Metal Forming, Powder Forming, Joining and Complex Design, Extrusion, Applied Ultrasonic Metal Working Processes and Technologies, Die and Mold Engineering, Computational Mechanics in Material Processing, Wire Drawing, Nano/Micro Processing, Porous Materials, and Forming Technology of Biomedical Materials. Articles of 10–20 are annually published through JSTP in Materials Transactions: for example, 16 articles in 2021–2022.4,5,94–107)
The awarded paper of Takahashi et al.1,60) through JILM is concerned with measurements of interdiffusion and impurity-diffusion coefficients in multicomponent Ti alloys, which are fundamental quantities to understand phenomena occurring at elevated temperatures. Indeed, comprehensive study was presented on the Ti–Al–Zr ternary system following their earlier studies on the Ti–Al–X (X = V, Cr, Fe, Co) ternary systems.17–20) In association with the diffusivity measurement, readers find a paper reporting measurements of interdiffusion coefficients from Sm2Fe17/Zn diffusion couples,108) where Zn is used as a binder to increase magnetic properties of consolidated Sm2Fe17N3 powder. Measurement of Cu diffusion in Fe was also reported using atom probe tomography from Cu precipitation in an Fe–0.89 mol%Cu alloy, where it was feasible to cover the temperature as low as 390°C.109) According to an analysis of citation data in Web of Science, it should be noted that two diffusion papers have been well cited for the last 10 years, although they were published in 1961 and 1975. The former was written by Suzuoka entitled “Lattice and Grain Boundary Diffusion in Polycrystals”110) with 349 citation in the years from 2013 to 2022 and the latter by Onishi and Fujibuchi entitled “Reaction-Diffusion in the Cu–Sn System”111) with 206 citation for the same interval. It is well anticipated that the best paper by Takahashi et al.1) provides diffusivity data to contribute to the materials development.
Finally, comments are added to the two best papers for the young scientists.2,3) The paper by Tanaka et al.2) was well evaluated because they clarified nanocluster formation behavior important for the strengthening of Al–Mg–Si alloys. Their successive work was further published in the special issue edited for the presentations at ICAA18 as mentioned above.85) The paper by Ishii et al.3) gained good evaluation because they provided important information for designing heat-resistant Al–Mg–Zn alloys with extra addition of Cu or Ni.
