SEMI-SOLID METAL FORMING - MICROSTRUCTURAL DEVELOPMENT
Abstract
The success of the semi-solid processing of alloys depends on the achievement of suitable microstructure prior to deformation. Homogeneous flow in a semi-solid slurry is possible only with globular solid phase particles, which can be produced by vigorous agitation of the cooling alloy in the temperature range between the solidus and the liquidus or by partial remelting of a cold worked billet. In the former, the development of globules proceeds through fragmentation of the lateral dendrite arms, while the latter makes use of the grain refinement effect during the recrystalization. The fine globular microstructure behaves thixotropically during deformation in the semi-solid region. The thixotropical behaviour is based on the particle agglomeration and deagglomeration in dependance of the shear rate during the casting or forming process.
This contribution brings forth basic information on the mechanisms of microstructural development in both of the above mentioned processes.
Keywords: semi-solid metal forming|thixotropy|partial remelting|globularization|
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