The microstructural and constitutional evolution of cast dendritic ZA27 alloy during partial remelting

The microstructural and constitutional evolution process of cast dendritic ZA27 alloy during heating into the semi-solid state was studied by scanning electron microscopy and X-ray diffraction techniques. Dissolution of the interdendritic eutectic η-phase first took place towards the insides of the primary dendrites, resulting in the primary dendritic grains coarsening into interconnected non-dendritic grains. Subsequently, the residual interdendritic η-phase and the edges of the primary grains melted in succession, making the microstructure of the alloy change into a solid skeleton structure penetrated by liquid. Correspondingly, the phase transformations of α + η + ε → β, η + β → L, β → α ′ + L and α ′ → L occurred in turn during this process. In addition, special attention was paid to the formation of the liquid pools entrapped within the solid grains.