Grain Refinement of Aluminium Alloys: Recent Developments in Predicting the As‐Cast Grain Size of Alloys Refined by Al‐Ti‐B Master Alloys

Abstract

This paper presents the results of recent research on the grain refinement of aluminium alloys. There has been considerable development in our understanding of the mechanisms controlling grain refinement over the last decade and these will be briefly described. In particular, the Interdependence Model has clearly explained the interdependence between the growth of grains and the nucleation potency of refining particles in causing a wave of nucleation events throughout a casting. This interaction determines the final as-cast grain size. A key factor identified by this research is the formation of a nucleation-free zone in front of a growing grain that prevents nucleation up to the point where a critical amount of constitutional supercooling is established allowing the next nucleation event to occur. Thus, the grain size is determined by the size of the nucleation-free zone and the distance to the next most potent particle. The Interdependence Model can, therefore, be used to predict grain size changes with composition and nucleant particle density. In this paper the Interdependence Model is used to develop equations for predicting the grain size of aluminium alloys when refined by Al-Ti-B master alloys. The performance of Al-5Ti-1B and Al-3Ti-1B master alloys are compared in the light of the Model. Light Metals 2014

The Contribution of Constitutional Supercooling to Nucleation and Grain Formation

“…Figure 7(b) assumes a constant particle number density for all values of Q. If the particle number density also changes with each increment in Q then the value of xSd changes with Q as discussed previously 77 ..…”

“…For each alloy composition the theoretical limit of refinement is given by xnfz. For low Q values NFZ can contribute 50% or more to the grain size 10,77 . Figure 7(b) assumes a constant particle number density for all values of Q.…”

Evolution of the As‐Cast Grain Microstructure of an Ultrasonically Treated Al–2Cu Alloy

“…They fall into two categories. One is the inoculation of nucleants via master alloys and through modifying the alloying chemistry . The other is the application of external fields by physical means .…”