EFFECT OF RARE EARTH ADDITIONS ON THE TEXTURE OF WROUGHT MAGNESIUM ALLOYS: THE ROLE OF GRAIN BOUNDARY SEGREGATION

Magnesium alloys that contain certain rare-earth(RE) additions are known to have improved formability and this can be partly attributed to the different texture they display after recrystallisation. Previous experimental work has identified segregation of RE to grain boundaries and dislocations as being potentially important in producing this change in behaviour. In the present paper, two classical models (Langmuir-McClean and Cahn Lucke Stuwe) are used to explore the likely effect of RE additions on grain boundary solute concentration and drag. It is demonstrated that a wide range of RE elements are predicted to segregate strongly to grain boundaries due to the large atomic size misfit with magne- sium. The maximum level of segregation is produced for elements such as Y or Gd that combine a high misfit and high bulk solubility. Segregated Y is predicted to produce a solute drag pressure on migrating boundaries several orders of magnitude greater than that obtained by Al or Zn additions. It is demonstrated that whilst this drag is predicted to be insufficient to strongly retard static recrystallisation under typical annealing conditions, it is expected to suppress dynamic recrystallisation (DRX) by any mechanism requiring boundary migration.