Microstructural evolution and phase transformations of mechanically stirred non-dendritic ZA27 alloy during partial remelting

In recent years, a new forming technique, semi-solid forming, has been developed, in which metal alloys are processed at a temperature above their solidus but below their liquidus. The microstructural evolution and phase transformations of mechanically stirred non-dendritic ZA27 alloy during partial...

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Bibliographic Details
Published in:Journal of Wuhan University of Technology. Materials science edition 2004-12, Vol.19 (4), p.56-61
Main Authors: Ti-jun, Chen, Yuan, Hao, Jun, Sun
Format: Article
Language:English
Subjects:
Alloys
Dendritic structure
Evolution
Grains
Heat treating
Melting
Metallurgy
Microstructure
Phase transitions
Semisolids
X-ray diffraction
Zinc base alloys
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Summary:In recent years, a new forming technique, semi-solid forming, has been developed, in which metal alloys are processed at a temperature above their solidus but below their liquidus. The microstructural evolution and phase transformations of mechanically stirred non-dendritic ZA27 alloy during partial remelting were studied by using scanning electron microscopy and X-ray diffraction technique. The partial remelting temperature was 460C and lower than the stirring temperature of 465 deg C. So the microstructure with globular grains needed for semi-solid forming can not be obtained and the starting primary nondendritic grains change in turn to connect non-dendritic grains, long chain-like structures and finally to coarsen connect grains. However, the small near-equiaxed grains between the primary non-dendritic grains are evolved into small globular grains gradually, some of which are also attached to the primary non-dendritic grains during the subsequent heating. The X-ray diffraction results show that a series of phase transformations , alpha + eta + epsilon- > beta, eta + beta - > L, beta- > alpha' + L, alpha + eta + epsilon- > alpha' and alpha' - > L, occur successively during this process . The main reason why the starting primary non-dendritic grains do not separate into the needed independent globular grains is that the reactions of eta + beta- > L, and alpha'- > L do not occur or occur incompletely in the layers used to connect the primary non-dendritic grains.
ISSN:1000-2413
1993-0437
DOI:10.1007/BF02841370