27th Magnetic Materials Center Seminar
October 30, 2006, 10:30
7th floor seminar room, Sengen
Synthesis and characterization of Al-Nb alloys
B. S. Rao
Recently Al-base nanostructured materials gained greater attention because of their superior mechanical properties compared to conventional materials and because of their possible application in aerospace and automotive industries. In the current talk I would like to discuss what are the advantages and drawbacks that these materials are facing.
Al-Nb alloys present considerable strength and hardness being promising materials for structural applications and these are mainly used in coatings. Till to date there are no study of this system in Al-rich corner in nano scale. In my current work I am studying the effect of Nb on the mechanical properties of the material at nanometer grain size level. In the present talk I would like to discuss some of the results about this system.

Development of Al-Ni-La alloy by Spark Plasma Sintering
T. Sasaki
Al-Ni-La alloy is expected to show very high strength when the primary pure-Al phase is present in the amorphous matrix. However, the dimensions of Al-TM-RE (TM: Transition metal and RE: Rare earth) alloys, are currently limited to rapidly solidified powders or ribbons. Thus, increasing efforts have been focused on producing bulk forms that retain a nanocrystalline/amorphous microstructure after subsequent compaction and consolidation of the amorphous precursors (gas-atomized powders and melt-spun ribbons, etc.).
Spark Plasma Sintering (SPS) is known to be useful consolidation process rather than conventional process such as HIP, CIP and hot extrusion. The consolidation in SPS can be carried out at lower temperature and the higher density can be easily obtained. By taking advantage of the SPS method, the amorphous Al-Ni-La powder was consolidated to retain the amorphous phase after consolidation and the microstructure control was possible by subsequent heat treatment.
In the present study, the amorphous Al-Ni-La alloy containing primary pure-Al phase with very high density could be made by SPS process even at lower temperature than the crystallization temperature, 250 ℃. In addition, hardness of the alloy was increased by the subsequent heat treatment around the crystallization temperature. In the presentation, the variation in the mechanical property will be related with the microstructure change by the heat treatment.

Precipitation process in single- and double-aged Mg-Zn-Al alloys
K. Oishi
Mg-Zn alloys are most widely used wrought magnesium materials, and well known as a precipitation hardenable alloy system. The precipitation sequence has been studied from long ago. At the low aging temperature below 110 C, the formation of G.P. zone occurs, followed by the formation of beta1' and beta2' , precipitate, before reaching to the formation of equilibrium beta phase. To enhance the age hardening response, two-step aging was reported to be effective. Mg-Zn-Al alloys two-step aged were shown to increase yield strength in the tensile test, but the precipitation process in two-step aging has not been clarified yet. In this study, the variations of age hardening response and corresponding microstructures were investigated by using hardness test, transmission electron microscopy and three-dimensional atom probe.
The hardness of the two-step aged samples is higher than that of the single-aged samples for both alloys. The age hardening in the double aged samples appears at the early stage of aging. The two-step aged samples exhibit finer microstructure than the single-aged ones in both alloys. Peak aged Mg-6Zn-1Mn sample have two kinds of precipitates: one is a rod along to the c-axis of matrix phase, another is a plate lying on the basal plane. While Mg-6Zn-3Al-1Mn alloy shows rod-like and cuboidal precipitates. Atom probe analyses of both materials pre-aged at 70 C revealed the formation of Zn-rich zones. Therefore it is considered that their fine dispersed Zn-rich zones act as heterogeneous nucleation sites at the second aging, and results in finer microstructure.