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Identifying the Stages during Ultrasonic Processing that Reduce the Grain Size of Aluminum with Added Al3Ti1B Master Alloy
Author(s) -
Wang Gui,
Dargusch Matthew S.,
Eskin Dmitry G.,
StJohn David H.
Publication year - 2017
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201700264
Subject(s) - materials science , liquidus , ingot , equiaxed crystals , nucleation , grain size , acoustic streaming , alloy , metallurgy , aluminium , particle size distribution , cavitation , composite material , particle size , ultrasonic sensor , chemistry , physics , organic chemistry , acoustics , mechanics
The combined application of UST and Al3Ti1B grain refiner changes the macrostructure of untreated commercial purity aluminum from large millimeter sized columnar grains to equiaxed grains of a few hundred microns. This research reveals three distinct stages that affect the grain size, while UST is applied during melting and solidification. Stage I applied well above the liquidus temperature improves the efficiency of the refiner, possibly by de‐agglomeration and wetting of TiB 2 particles, and their distribution throughout the melt by acoustic streaming. Stage I is followed by Stage II, where little further improvement occurs. Stage III causes additional grain refinement when applied at and below the liquidus temperature, where nucleation of grains maybe enhanced by cavitation, which can also facilitate fragmentation and detachment of grains formed on the sonotrode. Convection due to acoustic streaming creates a uniformly undercooled temperature in the melt, which ensures the survival of these new grains during transport, as well as assisting the transport of grains to produce a uniform fine grain size throughout the ingot.