Effect of a high magnetic field on the morphological and crystallographic features of primary Al₆Mn phase formed during solidification process

Morphological and crystallographic effects of a high magnetic field on the primary Al6Mn phase formed during the solidification of hypereutectic Al-3.25wt%Mn were investigated. Without the field, the primary Al6Mn crystals are mainly concentrated in the lower part and reveal a dispersed needle-like shape. In three dimension, the needles are in the form of a quadrangular prism (laterally bound by {110} and preferentially growing along <001>). When the magnetic field is applied, they tend to be distributed homogenously and show some extra agglomerate- or chain-like forms (preferentially extending along <100>). Furthermore, they also tend to preferentially orient with <100> parallel to the field direction. The homogenous distribution is caused by the magnetic viscosity resistance force. The “agglomerates” or “chains” are the result of a “bifurcation effect” due to the breakdown at the sharp edges of the quadrangular prisms. The preferential orientation should be attributed to the magnetocrystalline anisotropy of Al6Mn.