Effect of a high magnetic field on the growth of ternary Al-Cu-Ag alloys during directional solidification

Abstract

The influence of a high axial magnetic field (up to 6 T) on the solidification structure and crystallography in directionally solidified Al-21.5 wt%Cu-27 wt%Ag and Al-17.6 wt%Cu-42.2 wt%Ag ternary alloys has been systematically studied. Both alloys followed its own typical solidification processes: two-phase univariant eutectic growth (L→α-Al+Al2Cu) and three-phase invariant eutectic growth (L→α-Al+Al2Cu+Ag2Al) for Al-21.5 wt%Cu-27 wt%Ag and Al-17.6 wt%Cu-42.2 wt%Ag, respectively. It is found that the solidification structure and the orientation relationship (OR) between eutectic phases are modified at lower growth speeds (R ≤ 3 μm/s) under the magnetic field (B ≥ 2 T). For univariant eutectic growth, the magnetic field refines eutectic cell and promotes the transform from cellular structure to planar structure, whereas for invariant eutectic growth, the magnetic field reduces the eutectic spacing and causes the formation of banded structure at lower growth speeds (R ≤ 0.8 μm/s). The magnetic field enhances the richness of the Ag solute in the liquid ahead of the quenched liquid/solid interface. In addition, the magnetic field modifies the preferred OR between Al2Cu and Ag2Al eutectic phases at lower growth speeds (R ≤ 3 μm/s) and induces the formation of the OR with higher interface energy. Modifications of the solidification structure and the OR under the magnetic field are attributed to the thermoelectric magnetic (TEM) effects and the changes in the interfacial energy caused by the magnetic field.