Microstructural modification of Sn–Bi and Sn–Bi–Al immiscible alloys by shearing

Sn–20 wt-%Bi and immiscible Sn–20 wt-%Bi–1 wt-%Al alloys were used to understand the effect of high-intensity shearing on microstructural refinement. Novel ACME (Axial Centrifugal Metal Expeller) shearing device, based on axial compressor and rotor–stator mechanism to generate high shear rate and intense turbulence, was used to condition the melts prior to solidification. Microstructure in the Sn–Bi alloy deviated from dendritic grains with coarse eutectic pockets under conventional solidification to compact grains with well-dispersed eutectic under semisolid-state shearing. Decreasing the shearing temperature and increasing shearing time increased the globularity of grains. Following shearing, remnant liquid solidified into fine grain structure. In the immiscible Sn–Bi–Al alloy, shearing produced uniform dispersion of refined Al-rich particles in Sn-rich matrix as opposed to severe segregation under conventional solidification. The primary effect of shearing appears to originate from the thermo-solutal homogenisation of the melt and its effect on interface stability during solidification

Rapid Quench in an Electrostatic Levitator

No abstract availabl

Synchrotron radiography studies of shear-induced dilation in semi-solid Al alloys and steels

An improved understanding of the response of solidifying microstructures to load is required to further minimize casting defects and optimize casting processes. This article overviews synchrotron radiography studies that directly measure the micromechanics of semisolid alloy deformation in a thin sample direct-shear cell. It is shown that shear-induced dilation (also known as Reynolds’ dilatancy) occurs in semisolid alloys with morphologies ranging from equiaxed-dendritic to globular, at solid fractions from the dendrite coherency point to ~90% solid, and it occurs in both Al alloys and carbon steels. Discrete-element method simulations that treat solidifying microstructures as granular materials are then used to explore the origins of dilatancy in semisolid alloys