Partially solidified zone

In all early works, it has been assumed that there exists two well-defined planner interfaces. However, in the actual experiments a partially solidified zone (P.S.Z.) or mushy region and a partially melted zone (P.M.Z.) always exist between the completely resolidified and fresh solids. The existence of a P.S.Z. (mushy region) behind the freezing front is especially important since it offers the greatest resistance to the forward solute transfer and can trap the solute flowing backward and can affect the nature and the extent of macrosegregation. ... 

The thickness of a partially solidified zone (mushy region) in zone refining under most experimental conditions has been determined. The transfer of solute within this zone is, no doubt, most important in determining the overall solute transfer. All the zone refining theories have failed to take this most important factor into account. 

Using the proposed model along with the two generalized correlations for the experimental transmission coefficients in the partially solidified zone, a fairly close prediction of the solute redistribution (macro-segregation) of eutectic-forming mixtures after a single zone pass can be made. 

Welded microstructures can be extremely complex and often change drastically over a very short distance. The fusion zone or weld metal is a dendritic structure that has solidified from a molten state. Bordering the fusion zone are transition, unmixed and partially melted zones, and the heat-affected zone (HAZ). These zones can be reheated and altered by subsequent weld passes, in multipass welding. For alloys with structures that depend strongly on thermal history, such as steels, the final microstructure can be extremely complex. Since welded structures are often quite susceptible to corrosion, overalloyed filler metals are often used to enhance the weld corrosion resistance. For stainless steels with sufficiently high carbon content, sensitization in the HAZ is another major problem. (Frankel)5... 

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