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Volume 22, Issue 9
Displaying 1-7 of 7 articles from this issue
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Toshiro KOBAYASHI, Koichi TAKAI1972 Volume 22 Issue 9 Pages 541-554
Published: September 30, 1972
Released on J-STAGE: July 23, 2008
JOURNAL FREE ACCESSAluminum alloys have recently been used as cryogenic structural materials. The purpose of the present paper is to study tensile properties and behavior at impact test of T-4 treated Al-Zn-Mg, annealed Al-Mg and T-6 treated Al-Mg-Si alloys between room temperature and -196°C.
Although no distinct reduction of ductility was observed in tensile test at low temperatures, instrumented Charpy impact test of Al-Zn-Mg and Al-Mg alloys showed a reduction of notch toughness at -196°C: Toughness was good in the following order; Al-Mg alloy> Al-Zn-Mg alloy> Al-Mg-Si alloy.
Low temperature embrittlement of Al-Zn-Mg alloy was due to a decrease of crack-propagation energy. Crack-initiation and crack-propagotion energies were reduced in Al-Mg alloy. Low temperature fracture surfaces of these alloys showed laminated fracture facets. These facets were probably introduced by low temperature brittle fracture of precipitates at extremely elongated grain boundaries.
It was found that the unstable rapid fracture occurred in press boundary notch specimens of Al-Zn-Mg and Al-Mg-Si alloys. The fracture toughness value for these alloys was estimated to be about 1 kg-mm/mm2.View full abstractDownload PDF (3502K) -
Toshiro KOBAYASHI, Sueshige ISHIDA1972 Volume 22 Issue 9 Pages 555-563
Published: September 30, 1972
Released on J-STAGE: July 23, 2008
JOURNAL FREE ACCESSFollowing the previous study1), the present paper reports tensile properties and impact fracture characteristics of naturally aged TIG welds, 2-pass and 3-pass welds with welding rods of an Al-Mg alloy 5356, of T4-treated Al-Zn-Mg and annealed Al-Mg plates between room temperature and-196°C.
The instrumented Charpy test revealed that the impact values of the above two welds were fairly decreased at-196°C. It was found that this decrease was caused by the reduction in crack-initiation and crack-propagation energies. Further, the reduction of ductility in terms of the deflection in Charpy impact test was observed at -196°C.
Fracture load of Al-Zn-Mg alloy in Charpy tests was observed to increase at low temperature in the same manner as tensile strength in tensile test. On the contrary, fracture load of Al-Mg alloy welds in Charpy test decreased at -196°C. This phenomenon had also been observed in mother plate1) and was believed to be characteristic of Al-Mg alloy.
Low temperature brittleness in welds was more remarkable than that in mother plates. It was shown from the fractographic observation that this embrittlement was caused by the intergranular or the interdendritic brittle fracture.View full abstractDownload PDF (2752K) -
Michihiro TAGAMI, Yo SERITA1972 Volume 22 Issue 9 Pages 564-570
Published: September 30, 1972
Released on J-STAGE: July 23, 2008
JOURNAL FREE ACCESSSulphur addition was known to have a refining effect on primary silicon in hypereutectic Al-Si alloys. The purpose of this study is to clarify effects of an amount of S addition, holding time and superheating temperature on refinement of primary silicon crystals in an Al-20%Si alloy. Grain size of primary silicon and microstructure were observed by an optical microscope and an X-ray microprobe analyzer.
When a melt was held at 900°C for 10min, addition of 0.3-0.4%S resulted in refinement of primary silicon. Ten minute holding at 900°C after a modification treatment increased a refinining effect significantly. However, longer holding did not introduce improvement of a refining effect. The finest silicon crystals were obtained when a melt, modified by 0.3%S, was superheated at 1100°C for 10min. In the S-treated specimens, grey colored particles were seen at the center and the boundary of the primary silicon and in the eutectic structure. A microanalysis showed these particles to contain two components, Al and S. On a cooling curve of a modified specimen, a clear break was observed and was identified with a point, at which the primary silicon was nucleated. These results were interpreted in a manner similar to the AlP nucleation theory of primary silicon crystals.View full abstractDownload PDF (2912K) -
Tadakazu OHNISHI, Yoshizo NAKATANI, Kyoji SHIMIZU1972 Volume 22 Issue 9 Pages 571-575
Published: September 30, 1972
Released on J-STAGE: July 23, 2008
JOURNAL FREE ACCESSThe crystal structure of the ternary compound G in the Al-Mn-Cr system was studied in an effort to determine the phase diagram. It was shown that the G phase had a body-centered cubic lattice with composition of (Mn, Cr) Al12 and the lattice parameter was 7.509±0.001Å. The space group was Im3, where Al atoms occupied the 24 g-point positions (atomic positional parameter was y = 0.181 and z = 0.303), while Mn and Cr atoms occupied the 2a-point positions. Diffraction lines, which had been observed with uncertainty in indexing in the previous works, were not seen in the present study. It was considered that these lines were probably due to heterogeneity in composition in the G phase.View full abstractDownload PDF (609K) -
Hisashi SUZUKI, Motohiro KANNO, Kazuyoshi FUKUNAGA1972 Volume 22 Issue 9 Pages 576-583
Published: September 30, 1972
Released on J-STAGE: July 23, 2008
JOURNAL FREE ACCESSIt is widely known that the aging rate of Al-Cu-Sn alloy with a small addition of Sn is remarkably suppressed at low temperatures. However, the present authors' study on aging of Al-Zn-Mg alloy came to the conclusion that the vacancy-trapping model which had been proposed to explain the suppressed aging of Al-Cu-Sn alloy is uncertain. Therefore, the mechanism of this suppression was studied in this report.
The specimens used were two types of alloys with 3 and 4wt% Cu. In each type of alloys 14 sorts of speci mens with various amounts of Sn(0 to 0.25wt%) were prepared. The isothermal cross section at the Al corner of the equilibrium diagram of the Al-Cu-Sn ternary system was studied. Based on this diagram, aging experiments were carried out with special attention on whether a specimen consisted surfely of a single phase. The results obtained were as follows:
(1) An experimentally determined cross section of the phase diagram at 520°C showed that Al-Cu-Sn alloys rarely existed in a single phase even when a very small amount of Sn was added. In other words, ordinary Al-Cu-Sn alloys with a small addition of Sn consisted of two or three phases at solution temperatures. This resulted in a sharp decrease of Cu contents in the α phase.
(2) When the specimens were of one-phase, suppression of the aging rate was never observed at low temperatures. However, the aging rate of two-phase alloys decreased remarkably, as the amount of Sn increased. This indicates that suppression of aging in Al Cu-Sn alloys was directly related to the decrease of solubility of Cu in the α phase.
(3) Thus, the vacancy-trapping model, which had been proposed to explain the suppressed aging rate by assuming the interaction of the third element with the quenched-in vacancies, was proved to be erroneous. The binding energy between Sn atoms and vacancies was estimated to be less than or at most equal to that between Cu atoms and vacancies.View full abstractDownload PDF (1030K) -
Takakado NAKAYAMA1972 Volume 22 Issue 9 Pages 584-597
Published: September 30, 1972
Released on J-STAGE: July 23, 2008
JOURNAL FREE ACCESSDownload PDF (2918K) -
Shiro ISHIDA1972 Volume 22 Issue 9 Pages i-ii
Published: September 30, 1972
Released on J-STAGE: July 23, 2008
JOURNAL FREE ACCESSDownload PDF (347K)
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