44th Magnetic Materials Center Seminar
April 27, 2007, 9:00
7th floor seminar room, Sengen
Wrought processing and further investigation on microalloying effect of precipitation behavior in Mg-Sn based alloy
T. Sasaki
In precipitation hardening research of Mg-Sn based alloy, the study is going on from these two aspects;

1) Wrought processing of precipitation hardenable Mg-Sn alloy
2) Further investigation of microalloying effect

In the present talk, the progress on both topics will be reported briefly. In the wrought processing, Mg-Sn-Zn rolled alloy sheet was fabricated by both cold working process and hot working process. As a result of mechanical testing of hot worked alloy, 255MPa in yield strength and 300MPa in tensile strength was achieved in as-rolled state due to the grain refinement effect. The relationship between microstructure and mechanical property will be further discussed.
In the alloy search, effect of Zr-addition on hardening response will be presented in several Mg-Sn(-Zn)-X alloys and Mg-Sn-Zn-X (X=Zn, Ag, Ca etc,) alloys. Decrease in hardening response was observed in most of Zr-containing alloy to compare to Zr-free alloys. This is because of the formation of intermetallic particles between Sn and Zr. Exceptionally, very high hardening response was obtained in Mg-Sn-Zn-Ca-Ag-Zr alloy because of the grain refinement and the change in the size and morphology of precipitates.

Microstructure characterization of precipitates in Mg-Gd alloys containing Zn
K. Oishi
According to previous studies on Mg alloys containing rare earth elements, Mg-Gd alloys show excellent age hardening response and high strength at ambient and high temperatures. Most of Mg-Gd alloys include high Gd concentrations, over ~2at%Gd. But, Nie et al. [1] reported recently that the age hardening response and creep strength of Mg-1Gd-0.17Zr (at%) alloy were enhanced by the addition of 0.4at%Zn to the alloy. This is because the addition of 0.4at%Zn to the Mg-1Gd-0.17Zr alloy leads to refinement and homogeneous distributions of precipitates. In present work the structures and compositions of precipitates in the Mg-1Gd-0.4Zn-0.17Zr alloy were investigated using TEM and 3DAP. The plate-like precipitates observed in the alloy form on the basal planes, and have two different shapes, short and long ones. HAADF-STEM results showed that the precipitates consist of different atomic stacking.
[1] J.F.Nie, X.Gao and S.M.Zhu: Scr. Mater., 53(2005), 1049.

Phase separation in metallic glasses
B.J. Park
Phase separating systems presented a unique opportunity for designing composites with hierarchical microstructure. The first microstructural approach of the separated two amorphous phase has been reported in the (La-Zr)-Cu-Ni-Al metallic glass system[1]. Since the first report, we reported the synthesis of a phase separating glass in (Zr-Y)-Al-Co bulk metallic glass system, with a bulk glass forming ability which is important factor for structured materials.[2] Some other studies of two amorphous phase separation have also been reported. Recently, we try to further extent the phase separation in metallic glass forming system, i.e. three amorphous phase separation. So far, only thermodynamic simulation results of three phase separation have been published. And no experimental result on three phase separation has been reported.
We suggested (ZrAlCo)-(YAlCo)-(TiAlCo), (LaAlCo)-(YAlCo)-(Ti(Zr)AlCo) pseudo ternary system has the possibility of three amorphous phase separation by thermodynamic calculation.
The transmission electron microscopy has the limit of showing the three different contrasts from phase separated microstructure. We believe the 3D atom probe apparatus at NIMS would be one of the strongest tools to show the existence of three amorphous phases. The three phase separation result will open a new avenue for the microstructure control in the material science field.
[1]A.A. Kundig, M. Ohnuma, D.H. Ping, T. Ohkubo, and K. Hono, Acta Materialia 52, 2441 (2004)
[2]Byung Joo Park, Hye Jung Chang, Do Hyang Kim, Won Tae Kim, Kamanio Chattopadhyay, T.A.Abinandanan and Saswata Bhattacharyya, Physical Review Letters, 96, 245503 (2006)