Identifying the Stages during Ultrasonic Processing that Reduce the Grain Size of Aluminum with Added Al3Ti1B Master Alloy1 . Issue 8 (29th May 2017)

• Record Type: Journal Article
• Authors: Wang, Gui; Dargusch, Matthew S.; Eskin, Dmitry G.; StJohn, David H.
• Is Part Of: Advanced engineering materials. Volume 19:Issue 8(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-05-29
• Subjects: Materials -- Periodicals; 620.11
• DOI: 10.1002/adem.201700264
• Languages: English
• ISSNs: 1438-1656

Abstract

Abstract : 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 TiB2 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. Abstract : Termination of ultrasonic treatment of Al with Al3Ti1B master alloy addition at a range of temperatures reveals three stages affecting grain refinement. The grain density is increased by five to ten times during stages I and III, which are above and below the liquidus temperature, respectively. The grain size decreased from 278 to 115 microns after 110 s of treatment.