The cooling rate effects on the Nb-B inoculant potential of refining grains and dendritic scale in 6201 alloy

Abstract

Nb-B refiners are thought to be more stable than Ti-based refiners, becoming promising inoculants for Al alloys. However, the combined effect of adding NbB on dendritic scale and grain size (GS) with a wide range of solidification cooling rates remains unknown. It is well known that the shape of the α-Al phase is determined by a balance between inoculating components content/type and cooling rate. The inoculation of Al alloys with Ti-based inoculants, for example, significantly lowers GS while having no significant effect on secondary dendritic arm spacing (SDAS). Increased cooling rate, on the other hand, results in grain refinement, but only to a limited extent. Because of a combination of appropriate mechanical properties and suitable electrical conductivity, the 6201 alloy is widely employed in the transmission and distribution of electricity. Despite being a thermomechanically treated alloy, it goes through a melting and solidification process first, which entail research on this level of processing. ln order to assess the impact of adding NbB to the 6201 alloy’s refinement level (either macro or microscopic), directional solidification (DS) and centrifugal casting (CC) processes were utilized to obtain samples for examination. For the DS samples, cooling rates were determined, whereas for the CC samples, they were approximated for two alloys: 6201 (reference) and 6201-0.5wt.%Nb-0.1wt.%B alloys. Comparing the refined and non-refined alloy results, the GS of the DS 6201-NbB alloy was much smaller (about 13 times) across a range of cooling rates from 0.5 K/s to 20 K/s, whereas only 3 times smaller GS values were detected for CC samples at higher cooling rates. For particular cooling rates of 2.5 K/s and 240 K/s, the GS/SDAS ratios of values related to slow and fast cooling were 6.9 and 6.2, demonstrating that the cooling rate sensitivity of both GS and SDAS was similar in the NbB-inoculated alloy.