Journal of Japan Institute of Light Metals
Online ISSN : 1880-8018
Print ISSN : 0451-5994
ISSN-L : 0451-5994
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Volume 56, Issue 11
Displaying 1-18 of 18 articles from this issue
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REVIEW
RESEARCH REPORT
  • Effects of precipitate microstructures near grain boundaries on strength and ductility in Al–Zn–Mg(–Ag) alloys
    Tomo OGURA, Shoichi HIROSAWA, Tatsuo SATO
    2006 Volume 56 Issue 11 Pages 644-650
    Published: 2006
    Released on J-STAGE: January 07, 2007
    DOIhttps://doi.org/10.2464/jilm.56.644
    JOURNAL FREE ACCESS
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    The relationship between strength, ductility and precipitate microstructures in the vicinity of grain boundaries was evaluated for Al–4.9%Zn–1.8%Mg(–0.3%Ag) (in mass%) alloys using transmission electron microscopy (TEM), three-dimensional atom probe (3DAP) and tensile test. In the ternary alloy aged at 433 K, larger widths of precipitate free zones (PFZ) were observed by TEM and elongation was smaller, regardless of the size of grain boundary precipitates. On the other hand, in the ternary and Ag-added alloys aged at 373 and 393 K, elongation was larger due to both of the much smaller widths of PFZ and the much smaller size of grain boundary precipitates. These suggest that the presence of PFZ is harmful to the fracture of the investigated alloys. The measured proof stress and elongation were correlated to the width of PFZ and size of grain boundary precipitates, enabling a quantitative prediction of tensile properties from the corresponding microstructural parameters. Furthermore, on the basis of a 3DAP analysis result of the grain interior region where Ag atoms are condensed within nanoclusters of Zn and Mg, it was also proposed that Ag atoms around grain boundaries efficiently trap Zn and Mg atoms, resulting in the prevention of both solute depletion and widening of PFZ.
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  • Effect of reversion process on tube expansion of an Al–Zn–Mg–Cu alloy in T4 temper
    Yasuhiro NAKAI, Tadashi MINODA, Shinichi MATSUDA, Hideo YOSHIDA
    2006 Volume 56 Issue 11 Pages 651-654
    Published: 2006
    Released on J-STAGE: January 07, 2007
    DOIhttps://doi.org/10.2464/jilm.56.651
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    Severe working is required for structural materials in some cases for the purpose of reducing costs. The cost becomes higher with the increasing production process when working from O temper condition; therefore working from T4 temper condition is then desirable. In this study, the effect of the reversion process on the cold workability, especially the expanding of an Al–Zn–Mg–Cu alloy tube in T4 temper was investigated. The suitable condition of reversion treatment on which the hardness decreased and the workability which had decreased by long term room temperature aging improved was 433 K for 45 s. In the case of long time reversion at relatively low temperature, e. g., 393 K for 3600 s, the workability became better than that without the reversion treatment while the hardness after the reversion treatment became equal to that without the reversion treatment. Improvement of workability is due to the homogeneous deformation owing to the second–phase particles (η′and η phase) which precipitated during the reversion heat treatment. It was then suggested that the reversion heat treatment at a relatively lower temperature for a longer time could be industrially useful.
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  • 3DAP analysis of composition of metastable precipitates in Al–Zn–Mg based alloys
    Hidenori NAKO, Kozo OSAMURA, Hiroki ADACHI, Kazuhiro HONO, Tadakatsu O ...
    2006 Volume 56 Issue 11 Pages 655-661
    Published: 2006
    Released on J-STAGE: January 07, 2007
    DOIhttps://doi.org/10.2464/jilm.56.655
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    Metastable precipitates play important roles in a super high strength Al–Zn–Mg based alloy (Mesoalite®). The present study was undertaken to examine the composition of the metastable precipitates in Mesoalite® and the effect of Mn addition on the composition. The (Zn+Mg) concentration of η′ metastable precipitates detected by 3DAP (three dimensional atom probe) was ~25% in the alloy Al–4.1Zn–3.1Mg–0.57Cu–0.01Ag (at%). By comparing with the results of G.P. zones in an Al–Zn alloy, it was suggested that the intrusion of Al atoms from the matrix lowered the (Zn+Mg) concentration of metastable precipitates detected by 3DAP. A model to quantify the intrusion of Al atoms was developed and applied to the metastable precipitates. The (Zn+Mg) concentration was quantified to be ~65 at% at 383 K and ~75 at% at 413 K. When the alloy contained Mn, furthermore, it was suggested that Mn affected the Zn/Mg ratio of metastable precipitates by lowering the virtual Zn/Mg ratio of the specimen composition.
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  • 3DAP nano-scale analysis of solute clusters formed in a naturally aged Al–Zn alloy
    Yoshiki KOMIYA, Shoichi HIROSAWA, Tatsuo SATO
    2006 Volume 56 Issue 11 Pages 662-666
    Published: 2006
    Released on J-STAGE: January 07, 2007
    DOIhttps://doi.org/10.2464/jilm.56.662
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    A three-dimensional atom probe (3DAP) analysis is an efficient method in clarifying clustering behaviors of solute atoms. In this work, the shape and concentration of solute clusters in the early stage of low temperature aging were investigated for an Al–4.9mol%Zn alloy by the 3DAP analysis. The solute clusters in the alloy aged at 293 K were successfully detected and the growth behavior during aging was observed from the 3DAP maps. The shape of solute clusters depends on their sizes; i.e. the smaller clusters are in a spherical shape and the larger ones possess an ellipsoidal shape. Although larger solute clusters have a constant Zn concentration corresponding to the miscibility gap of GP zones, the solute concentration inside smaller solute clusters significantly varied.
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  • Two-step aging behaviors of Al–Mg–Si alloy extrusions
    Hidenori HATTA, Shinichi MATSUDA, Hideo YOSHIDA
    2006 Volume 56 Issue 11 Pages 667-672
    Published: 2006
    Released on J-STAGE: January 07, 2007
    DOIhttps://doi.org/10.2464/jilm.56.667
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    The two-step aging behaviors of various Al–Mg–Si alloy extrusions have been studied mainly by tensile testing, differential scanning calorimetric analysis (DSC) and electrical resistance measurements. The natural aging at 5°C, 20°C and 40°C for 86.4 ks has a beneficial effect on the strength after artificial aging of the low Mg2Si containing alloys. On the other hand, the natural aging has a negative effect on the strength after artificial aging of the high Mg2Si containing alloys. The β″ peak on the DSC curve shifts to a higher temperature with natural aging for the high Mg2Si alloy. However, no β″ peak was found for the low Mg2Si alloy. This suggests that there is no negative effect dominated by β″ phase for the lower Mg2Si alloys.
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  • Effects of Ag addition on age-hardening and nano-scale precipitate microstructures of an Al–3%Mg–1%Cu alloy
    Shoichi HIROSAWA, Tomoya OMURA, Tatsuo SATO, Yoshikazu SUZUKI
    2006 Volume 56 Issue 11 Pages 673-679
    Published: 2006
    Released on J-STAGE: January 07, 2007
    DOIhttps://doi.org/10.2464/jilm.56.673
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    In this work, the bake-hardening (BH) response of Al–3.0%Mg–1.0%Cu alloys with and without Ag has been investigated by a hardness test, and related to the nano-scale precipitate microstructures observed by high resolution transmission electron microscopy (HRTEM) and a three-dimensional atom probe (3DAP). The small addition of Ag increased hardness under a BH condition (e.g. 443 K for 1.2 ks) due to the rapidly formed nanoclusters containing Mg, Ag and/or Cu. The formation of the equiaxed Z phase was also accelerated by the Mg/Cu/Ag clusters, resulting in the more increased second-stage hardening. This strongly suggests that Mg/Cu/Ag clusters provide effective nucleation sites for the Z phase, whereas Mg/Cu clusters formed in the ternary alloy do less.
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  • HRTEM observation of precipitates in an Al–1.1mass%Mg2Ge alloy
    Kenji MATSUDA, Teruyoshi MUNEKATA, Tokimasa KAWABATA, Yasuhiro UETANI, ...
    2006 Volume 56 Issue 11 Pages 680-684
    Published: 2006
    Released on J-STAGE: January 07, 2007
    DOIhttps://doi.org/10.2464/jilm.56.680
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    Rod-shaped precipitates in Al–1.1mass%Mg2Ge (Al–0.52at%Mg–0.24at%Ge) alloy aged at 523 K were observed by high-resolution transmission electron microscope (HRTEM) to understand their crystal lattices and chemical compositions. Rod-shaped precipitates were parallel to &lsaquo;100&rsaquo; directions of the matrix. There were 2 groups for rod-shaped precipitates, namely, small cross sections about 10 nm and large ones over 20 nm in diameter. Small precipitates showed a hexagonal network of bright dots in their HRTEM images, and its crystal lattice was estimated as a hexagonal having a=0.72 and c=0.405 nm based on analysis of HRTEM images and selected area electron diffraction (SAED) patterns. This lattice parameter was slight larger than that of the β′-phase in Al–Mg–Si alloy. Its orientation relationship with the matrix was as follows: {0001}p//{001}m, &lsaquo;1120&rsaquo;p//&lsaquo;100&rsaquo;m. Precipitates having large cross section showed a rectangular network having 0.68 and 0.35 nm. This was similar feature to the A-type precipitate in the Al–Mg–Si alloy with excess Si. A crystal lattice of this precipitate was estimated as a hexagonal having a=0.405 and c=0.68 nm based on analysis of HRTEM images and SAED patterns. Mg and Ge elements were detected from these precipitates by energy dispersive X-ray spectroscopy (EDS) and the ratio of Mg to Ge (Mg/Ge) for the small precipitate which is similar to the β′-phase in Al–Mg–Si alloy, was about 3, not 2. The Mg/Ge for large precipitates which are similar to the A-type precipitate in Al–Mg–Si alloy was 2, and this ratio was larger than that of the A-type precipitate in Al–Mg–Si alloy. It has been expected that these differences of chemical composition for precipitates caused the increment of lattice parameters of precipitates in Al–Mg–Ge alloy.
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