Grain refinement of Al–Si alloys by Nb–B inoculation. Part I: Concept development and effect on binary alloys

Heterogeneous Nb-Based Nuclei for the Grain Refinement of Al-Si Alloys

“…NbB 2 and Al 3 Nb), we analysed crystallographic databases and found that Nb-based intermetallics, which have an isomorphous structure and similar lattice parameters to the respective Ti-based compounds, would be successful candidates as heterogeneous nucleation substrates for Al-Si alloys. 15 In our first works, 16,17 in which the Nb-based intermetallics were formed by adding Nb powder and KBF 4 flux to Al-Si alloys, we demonstrated the grain refining potency of Nbbased intermetallics on Al-Si alloys. The grain refinement is not hindered even though niobium can form silicides, as these intermetallic phases are stable at much higher temperatures with respect to their Ti-based counterparts.…”

“…This means that their kinetics are much slower, in particular at processing temperatures typically used in Al foundries, and, thus, no poisoning was detected. 16,17 In this work, we focused on the development of an Al(96)-Nb(2)-B(2) master alloy, which has been found to be easier to add to the melt, starting from a different source of raw materials [i.e. Nb powder and Al(95)-B(5) master alloy].…”

Potential of an Al-Ti-MgAl2O4 Master Alloy and Ultrasonic Cavitation in the Grain Refinement of a Cast Aluminum Alloy

“…From these cooling curves, the nucleation temperature (T n ) of primary Al crystals is identified from the first derivative of the temperature (dT/dt) curve, where the slope of the T-t curve starts to deviate. [10] The other two characteristic temperatures are (1) T min , unsteady state growth temperature or the onset of recalescence, when the latent heat of solidification surpasses the heat extracted from the sample by cooling; and (2) T g , the end of recalescence or the onset of steady state growth of primary (Al) dendrites. Consequently, the undercooling of the primary (Al) nucleation can be approximated as DT = (T g -T min ).…”

“…Consequently, the undercooling of the primary (Al) nucleation can be approximated as DT = (T g -T min ). [10] In the alloy without master alloys addition (Figure 15 (a)), the (Al) primary phase starts to nucleate at 893 K (620°C) and ends at 891.5 K (618.5°C). The maximum nucleation undercooling from the recalescence was calculated to be 1.5 K (1.5°C).…”

“…), and/or growth-restricting alloying elements (Ti, V, Nb, etc.). [6][7][8][9][10] In current industrial practice, Al-Ti-B (Al-Ti-TiB 2 ) and Al-Ti-C (Al-Ti-TiC) master alloys are the most common grain refiners used in cast and wrought Al alloys. [2,3] The grain refinement mechanisms as well as some technological issues related to Si or Zr poisoning of Al-Ti-B grain refiners are thoroughly scrutinized by theoretical models and experiments.…”