Grain refinement of Al alloys: Mechanisms determining as-cast grain size in directional solidification

Model of Dendrite Growth in Metallic Alloys

“…(1) was successively applied during grain refinement modelling which was based on free growth model [3,10].…”

“…Mentioned models connects the dendrite tip growth rate with physicochemical parameters and solutal undercooling. In this work the following model was chosen [15,10]: In this case, ΔT S , is assumed to be only force for dendrite tip growth and it can be calculated as: ] is imposed cooling rate that can be described with any function or be set to constant [3,10].…”

“…Prepared model can be useful even in the case of compound alloy while it is possible to reduce it to binary alloy according to additivity rule [9,10]. As in Rappaz and Thevoz [2] work it was assumed that dendrite grows inside the spherical envelope of radius R, that consists its arms and surrounding liquid.…”

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

“…[39] Maximum DT cs for CP Al at a typical solidification velocity was calculated to be 2.8 K (2.8°C) and assumed to be higher for more solute-containing alloys. [40] The measured thermal undercooling is very small in the case of spinel-inoculated alloys ( Figure 15). This means that the solutal component of undercooling plays the most essential role in nucleation on the MgAl 2 O 4 substrates.…”

“…It is well known that with a spread of particle sizes, grain initiation events are also spread over a range of undercooling. [39,40] A few early nucleation events triggered by larger particles can then lead to grain growth and latent heat evolution, rendering many smaller particles inactive. In was shown that in the Al-5Ti-1B master alloy, active TiB 2 particles constitute around 40 vol pct of the particles population but the number efficiency of optimum sized particles is less than 1 pct.…”